Wavetek 148A User Manual

INSTRUCTION MANUAL

MODEL 148A

MHz

20

AM/FM/PM GENERATOR

@ -

1981. - Wavetek

THIS DOCUMENT CONTAINS INFORMATION PRO-

PRIETARY TO WAVETEK AND IS SOLELY FOR IN-

STRUMENT OPERATION AND MAINTENANCE. THE

INFORMATION IN THIS DOCUMENT MAY NOT BE
DUPLICATED IN ANY MANNER WITHOUT THE
PRIOR APPROVAL IN WRITING OF WAVETEK.

SAN DIEGO

9045 Balboa Ave., San Diego, CA 92123
P.O. Box 661, San Diego,

’

Tel

7141279-2200

TWX 91w352oo7

Calif.

.

92112

hhuat

Instrument Retease

l3eeion 6181

A-3181

1.1 THE MODEL

Wavetek Model

148A

148A,

20 MHz AM/FM/PM Generator
is a precision source of sine, triangle, square, ramp
and pulse waveforms plus

dc

voltage. The waveforms
may be controlled in symmetry as well as amplitude
and dc offset. A built-in modulation generator can
modulate frequency, phase and amplitude or modula­tion may be by an external source.

The generator may be run in continuous mode or trig­gered for a single pulse or gated for a burst of pulses.
Triggering and gating may be by the Model 148 built-in
modulation generator or by

an

external source. The

triggered and gated waveform start/stop point is

- 90’

selectable from

through +

trol plus dc offset control gives haverwave

90’.

Start/stop con-

capability.

External Trigger:

Generator is quiescent until trig­gered by an external signal, then generates one cycle
at the selected frequency.

External Gate: Same as external trigger, except gen­erator oscillates at the selected frequency for the

duration of the positive state of the external signal
plus the time to complete the last cycle.

Internal Trigger: Same as external trigger, except that

the modulation generator is internally connected to
the trigger input of the main generator.

Internal Gate: Same as external gate, except that the

modulation generator is internally connected to the
trigger input of the main generator.

The main output of waveforms may be
offset. A TTL sync pulse is

available

attenuated

and

at main generator
frequencies, and the modulation generator waveforms
are available at fixed amplitudes.

Frequency of both the main generator and the
modulation generator can be manually controlled at
the front panel or electrically controlled by external

voltages.

1.2

SPECIFICATIONS

1.2.1

1.2.1.1

Main Generator

Waveforms

Selectable sine % , triangle 2/ , square %
positive square

J-L ,

negative square U- and dc. A
TTL sync pulse is provided on a separate output con­nector. All can be produced with variable symmetry,
amplitude and dc offset.

1.2.1.2

Operational Modes

Continuous: Generator oscillates continuously at the
selected frequency.

3

Modulation Modes

Internal Modulation

Setting a front panel modulation switch in the INT
position routes the selected modulation function from
the modulation amplitude control to the selected mod-

ulating circuits of the main generator.

Amplitude Modulation (AM):

lation functions are used in this

2/

2/ , ‘L

internal

mode. With modulation amplitude ccw, carrier at

function output is not amplitude modulated and ap-

proximately half of normal (AM OFF) amplitude.

Clockwise rotation of modulation amplitude results in

increasing amplitude modulation of the carrier to at
least 100% AM.

,

Frequency Modulation (FM) and Sweep:

m

modulation functions are used to linearly

sweep the main generator frequency. The frequency

dial sets the lower sweep limit and the modulation

amplitude control determines the upper frequency
limit (not to exceed 2.0 x multiplier). A sweep set

mode allows precision setting of upper frequency

limit. For frequency deviation, the dial determines the
center frequency and modulator
varies the main generator frequency above and below

modu-

modulation

M

/\I , 2/

or

and

\

l-l

center by an amount determined by the modulation
amplitude.

-Phase Modulation (PM): As in External Modulation.
Amplitude of modulator
varies phase up to

250’.

2/ , 2/ , \

functions

External Modulation

A BNC feeds an external signal to the modulating cir­cuits when selected by a front panel modulation tog­gle switch in the EXT position.

peak current and may be attenuated to 60 dB in 20
steps. An additional 20 dB vernier also controls the
waveform amplitudes.

1.2.1.6

Approximately
sine and triangle waveforms only).

1.2.1.7

Adjustable Waveform Start/Stop Point

- 90’

to +

90’

to 2 MHz (operative on

DC Output and DC Offset

dB

Amplitude Modulation (AM):
signals with zero dc component produce suppressed
carrier modulation; i.e., a carrier (at main generator
function output) amplitude of zero. The function out­put modulated signal has an amplitude sensitivity of
3 volts peak (1.5 Vp into

rier signal level at the function output can be pro­duced at a sensitivity of 3 Vp (I
dc component in. Modulating the dc component mod-

ulates the carrier level. Percent modulation (AM) will
be the ratio of the peak ac to peak dc of the modulating
signal. Input impedance is

Frequency Modulation (FM) and Sweep: Sensitivity is
20% of frequency range/volt peak. Linear behavior

results only when all instantaneous frequencies call­ed for fall within the frequency range (2
to 0.002
called for is the multiplier and dial setting altered by
the instantaneous voltage at the modulation input. In­put impedance is 5

Phase Modulation (PM): Sensitivity is
volt peak. Linear behavior results only when all instan­taneous transition frequencies called for fall within

the frequency range (2

plier).The

depend heavily on the modulation frequency. and

waveform. Inoperative at frequency multiplier settings

below 100. Input frequencies roll off at 6 dB/octave

above one half of full range frequency and above

150

1.2.1.4,

x

multiplier). The instantaneous frequency

instantaneous frequencies called for will

kHz.

Input impedance is IO

Frequency

5OQ)

kQ.

x

Range

External modulating

per volt peak in. A car-

.5

Vp into 500) per 1 Vp

>2.5 kQ.

x

multiplier

IO0

phase shift/

multiplier to 0.002 x multi-

kQ.

Selectable through function output
by front panel controls to a minimum of

t

14.4 Vdc( t 7.2 Vdc into
offset limited to k 15 Vdc ( t 7.5 Vdc into
set and wave form attenuated proportionately by the
60

dB

output attenuator.

1.2.1.8

AM: Sensitivity of 3 Vp

impedance is
FM: Sensitivity of 20% of frequency range/Vp. Input
impedance is 5
PM

:

pedance

1.2.1.9

Symmetry of all waveform outputs is continuously ad­justable from 1
variable duty-cycle pulses, sawtooth ramps and
symmetrical sine waves.

External Modulation Input

>2.5 k0.

kn.

Sensitivity

is 1O

of

kQ.

Symmetry

:1

9 to

When SYMMETRY control is used, in­dicated frequency is divided by
ima

tely IO.

500)

out/Vp (1.5V

IO0

phase

19:1.

Varying symmetry provides

NOTE

(5OQ).

Controlled

with signal peak plus

5OQ).

DC off-

into 503). Input

shift/VP.

Input im-

non-

approx-

1.2.1.10 Sync Output (TTL)

TTL level pulse which will drive 10
quency and time symmetry are the same as for func­tion output.

TTL

loads. Fre-

0.0002

approximately

1.2.1.5

s

(15V

into

1-2

Hz to 20 MHz in

1

%

Function Output

, 2/ and \ selectableandvariable

p-p into

5On).

5Os1). n

All waveforms and dc can supply 150

IO

overlapping ranges with

vernier control.

(500)

and u up to 15 Vp (7.5 Vp

to 30V

p-p

mA

1.2.1.11 Trlgger and Gate

Input Range: IV p-p to *
Input Impedance: IO
Pulse Width: 25 ns minimum.
Repetition Rate: IO MHz maximum.
Adjustable triggered signal start/stop point: approxi­mately-

90’

to

+90”

IOV.

k0,

33

pF.

to 2 MHz.

1.2.1 .12

Frequency Precision

1.2.2.3

Output

(6OOQ)

Dial Accuracy

+ (I

O/O

of setting + 1 % of full range) on x 100 thru

-

x 1 M ranges.

*+ (2% of setting + 2% of full range) on

-

x 10 and x

10M

ranges.

x

.Ol

Time Symmetry

t

0.5% on x 100 thru x IOOk

2.0 on dial.

t

5% on all other ranges and from 0.02 to 2.0 on dial.

1.2.1

.13

’

Amplitude Precision

Amplitude Change With

Sine variation less than:

t

0.1 dB thru x 1

-+

0.5 dB on x 1 M range;

t

3 dB on x 10M range.

OOk

ranges;

ranges and from 0.2 to

Frequency

’

Step Attenuator Accuracy

-

+

0.3 dB per 20 dB step at 2

1.2.1.14

Waveform Characteristics

kHz.

Sine Distortion

<0.5%

<
All harmonics 30
range.
All harmonics 26 dB below fundamental on x 10

range.

on x 100 Hz to x 10

1

.O%

on x

.01

to x 10 Hz and x 100

kHz.

kHz

ranges.

dB

below fundamental on x I MHz

thru

MHz

2/

, 2/ and ‘L are fixed level
about ground. M and
from 0 to +

1.2.2.4
Voltage control of modulator frequency with sensitivity

of 20% of range per volt. Input impedance is 5

1.2.2.5

5V.

Frequency Modulation (FM IN)

Waveform Characteristics

M

10V

p-p balanced

are fixed level 5 Vp

kQ.

Sine Distortion

<

5%

Time Symmetry
<

O/O

from 1 Hz

5%

from 0.1 Hz to 100

to 10

kHz.

kHz.

1.2.3 General

1.2.3.1

Stability (for amplitude, dc offset and

frequency)

Short Term:t 0.05% for 10 minutes.

Long Term:

1.2.3.2

Specifications apply at

will operate from

1.2.3.3

28.6

cm (11 ?4 in.) wide;

(103/4

in.) deep.

t,O.25O/o

for 24 hours.

Environmental

25°C t 5°C ambient

O°C

to 50°C ambient temperatures.

Dimensions

13.3

Instrument

cm

(5 % in.) high; 27.3 cm

Square Wave Rise/Fall Times

At

FUNCTION

OUT < 25

ns for

15V

p-p into a

5Ost

load.

Triangle Distortion

Odd harmonics within 15% of correct value to 2 MHz.

1.2.2

Modulation Generator

1.2.2.1

Selectable sine 2/ , triangle
ramp M and down ramp M

1.2.2.2

s,2/

ranges.

M, Nl

Waveforms

Frequency Range

,

21

Sweep:

Hzto100

0.1

0.2 Hz

to

2/

,

square ?J , up

.

kHzz

200

kHz

(2 x setting).

in

three

100:1

1.2.3.4
5 kg (11 lb) net; 6.6 kg (14% lb) shipping.

1.2.3.5

90 to
selectable;

Weight

Power

108 to

126V,

105V,,

48 to 400 Hz; less than 40 watts.

Unless otherwise noted, ail specifications
apply from
when FUNCTION OUT is at maximum and

5OQ

terminated, with SYMMETRY control
at OFF. Symmetry and vernier affect fre­quency calibration. Maximum possible
asymmetry is a function of frequency
setting.

198 to 231V and 216

NOTE

0.1

to 2.0 on frequency dial

to

252V

1-3

SECTION

OPERATION

3.1 CONTROLS AND CONNECTORS

The following item

3.1

.1

Main Generator

1

Frequency Dial

main generator.The setting on this dial
multiplied by the FREQ MULT
basic output frequency of the generator at the

FUNCTION OUT.6 and SYNC OUT 7
The FREQ VERNIER
the modulation generator also affect the main
generator frequency.

Mode

2

Switch

operating mode of the main generator as follows:
a.

EXT GATE Mode

quiescent until a proper gate signal is applied
at the EXTTRIG IN BNC 13 and then outputs

the selected signal for the duration of the gate

signal, plus the time to complete the last cycle

generated.

numbers are keyed

The

-

-

This outer switch selects the

frequency control of the

12

and, in some cases,

-

The main generator is

to figure

12

setting is the

3-1.

BNCs.

b. EXT TRIG

mode, except the main generator output is
one cycle of selected signal only.

c. CONT Mode - The output signal is continuous.

d.

INT TRIG -

cept the trigger signal is applied internally by

the modulation generator.

e. INT GATE

the gate signal is applied internally by the
modulation generator.

TRIGGER LEVEL

is a continuously variable adjustment of the trig­ger circuitry firing point. When full ccw, a

tive going pulse at approximately ­quired for triggering (see figure

cw position,

mately +
quired for triggering. In the GATE modes, the‘
generator will run continuously when the control

is cw of 12 o’clock.

Mode

-

Same as for EXT GATE

Same as for EXTTRIG mode, ex-

-

Same as for

Control -

a

positive going pulse at approxi-

7.5V

or more positive voltage is re-

EXT GATE,

This

inner control

7.5V

3-2).

In the full

except

posi-

is

re-

12
13

Figure 3-1

Controls

MOOULATION

and Connectors

GENERATOR

3-1

3.1.2

Modulation

FUNCTION Switch

14

Generator

-

This switch selects the
waveform output of the modulation generator.
Output is at the OUT BNC connector
also available internally to the main generator.
Waveforms are sine
square

(N\).

AMPLITUDE

sweep frequency.

( ‘% ),

ramp up (M) and ramp down

A SWP SET detent holds the OUT BNC at

control 14 level;

( /L ),

triangle

used

to set upper

16

and is

( 2/ ),

.

AM- The instantaneous amplitude of the out-

d

put signal varies with the instantaneous ampli-

tude of the modulation signal.

e.

FM- The instantaneous frequency of the out­put signal varies with the instantaneous ampli­tude of the modulation signal.

f

.

PM- The instantaneous phase of the output
signal varies with the instantaneous amplitude of
the modulation signal.

MOD AMPLITUDE Control - This inner con-

trol attenuates the modulation generator signal
that is internally fed to the main generator when
modulating. It has no effect during internal trig­gering or gating and it has no effect on the

16

OUT

FREQ/PERIOD

15

signal.

MULT Switch - This outer switch
(with ranges given in both frequency and period)
selects the modulation generator frequency/

period range.

-

VARIABLE Control

This inner control sets

the frequency/period within a range.

OUT

(6OOn)

16

Connector - This BNC is the

modulation generator waveform output: sine

( % ),

triangle

level

1OV p-p

balanced about ground and ramp

( 2/ )

and square

(5V p-p into

6OOQ)

waveforms

( ‘L )

fixed

( AA, M )

fixed level 0 to + 5 Vp waveform.
FM IN (5

17

kQ)

Connector - This BNC is

the input
for frequency modulation of the modulation
generator.

Sensitivity is 20% of frequency range

per volt in.

OPERATlON

32

.

convenience,

For

the generator operation has
been grouped in seven basic modes, from which
many variations and combinations are possible.
The following paragraphs give basic switch posi­tions for each mode and requirements and sug­gestions for operation.

.

g

3.2.1
When setting up the generator, it is advisable to

serve the output on an oscilloscope. Connect
TION

5OQ

-

The dc output can be set from + 15 Vdc

DC

- 15

to

Vdc (+ 7.5 Vdc to - 7.5 Vdc into

5OQ).

Continuous Operation

ob-

FUNC-

OUT to the scope input using a 500 cable and a

load. For continuous waveform output, select a
basic waveform at the desired frequency. Ensure the
modulation switches are set to OFF and the mode is
set to

CONT.

The output amplitude can be as great as

15V p.p;

attenuate as desired.

NOTE

use

For best waveform quality,
TENUATIO N
tion; then use

SWITC H

the

for gross attenua-

AMPLITUDE control for

the AT-

fine attenuation.

The waveform may be skewed to the left or right using
the SYMMETRY control; e.g., making a ramp
from a triangle

(

/G

.)

waveform.

( ,/1 )

/

NOTE

10

The output frequency is divided b y

when

the SYMMETRY control is switched from

the OFF position.

The dc level of the waveform may be varied with the

DC OFFSET control, but waveform clipping can occur.

NOTE

The basic modes of operation are:

a.

Continuous- A continuous output signal.

b

.

Triggered

-

One cycle of waveform for each

trigger signal.

C.

Gated

-

A “burst” of waveforms for the dura-

tion of each gate signal.

Waveform clipping will occur (OVERLOAD

LED will light), unless waveform amplitude

is decreased so

that

wavefor m

plus

offset

is less than 7.5 volts at the waveform peak.

3.2. 2

Triggered Operation

In triggered operation, there is one cycle of output for

each trigger signal input. For triggered operation, first

3-3

set up the generator for continuous operation (refer to
paragraph 3.2.1). The main generator may be trig-

gered internally by the modulation generator or trig-

gered by an external source. If an unmodulated
waveform is being output, the modulation generator is

free. to give the desired triggering frequency and

should be selected as the trigger source. Use any

modulation generator waveform as the trigger. Set the
modulation generator frequency for the desired trig­ger frequency and sync on the modulation generator
output.

NOT E

3.2.4

The TRIGGER LEVEL control
manually triggering or gating the generator. For

manually triggering (single cycles), the generator

mode should be EXT TRIG with no external signal in­put at the EXT TRIG IN connector. Each time TRIG­GER LEVEL is rotated cw through mid-position, one
triggered cycle will be generated. In EXT GATE mode,
the generator runs continuously as long as the TRIG­GER LEVEL is

Manual Triggering and Gating

can also be used

CW

of mid-position.

for

1. Trigger frequency must be slower than
the output waveform frequency.

2.

The MOD AMPLITUDE control has no
effect in

Rotate the TRIGGER LEVEL control to obtain a good
trigger. If the waveform start/stop point is to be other
than zero degrees, set the TRIG START/STOP control
as required. (See figure 3-3.) Haverwaves can be set

up using start/stop control and

-90°

s--

If external triggering is to be used, connect a repeti­tive signal with a positive going transition of greater
than one volt to EXT TRIG IN using a
the TRIGGER LEVEL control for proper triggering.

3.2. 3

In gated operation there is a “burst” of waveforms
lasting the duration of the gate pulse plus the time re­quired to complete the last cycle of waveform started.
Set up as for triggered operation (refer to paragraph 3.2.2)
and select a “trigger” signal whose duty time gives
the desired waveform burst.

AA

Figure

Gated Operation

INT

TRIG

and INT GATE modes.

dc

offset control.

HAVERSINES

_v

3-3..

Waveform Start/Stop Examples

5OQ

cable. Adjust

3.2.5

AM Operation

In amplitude modulation, the instantaneous amplitude
of the output signal varies with the instantaneous
amplitude of the modulation signal.

NOT E

The output waveform will be
LOAD LED will light) if any instantaneous
amplitude greater tha n
( t

7.5 volts into

Set up the generator as for continuous operation
(refer to paragraph 3.2.1). Switch to internal or exter­nal amplitude modulation. If internal, note that the car-

rier (main generator waveform) mean amplitude is
decreased to half. This is to prevent clipping
driving the output amplifier) when the carrier ampli­tude is modulated (increased and decreased) by
another signal. Set the modulation generator fre­quency to a lower frequency than the main generator
and sync the scope to the modulation generator output.
Set the modulator amplitude for a desired percentage
of amplitude modulation (0 to greater than 1
and set the main generator ATTENUATION and
AMPLITUDE controls for a desired amplitude of
modulated waveform. If external modulation is
selected, observe that the carrier (main generator
waveform) amplitude drops to zero (null). This is for
suppressed carrier mode of amplitude modulation.
Connect the modulator OUT

IN with a coaxial cable. Set the main generator
ATTENUATION and AMPLITUDE controls
amplitude of suppressed carrier waveform. For best

results when using an external modulation signal at

EXT MOD IN, maintain as near as convenient
amplitude (which does not exceed 5
main generator ATTENUATION and AMPLITUDE con­trols. An external source may also be used for regular
AM operation, rather than suppressed carrier opera­tion, by supplying a dc component along with the ac

5OQ )

is produced.

clipped(OVER-

t

15 volt s

(6OOQ)

to the EXT MOD

VP);

(over-

00%

range)

for

a desired

a

5 Vp

then use the

3-4

modulating signal (observing 5 Vp limit) to set the car-

rier level.

MAIN DIAL

SETTING

AMPLlTUDE

MOD

MOD IN

EXT

OUTPUT

FREQUENCY

FACTOR*

FM Operation

3.2.6
In FM operation, the instantaneous frequency of the

output signal varies with the instantaneous amplitude
of the modulating signal.

NOTE

The

output

frequency modulation will not
be linear when the instantaneous
modulated frequency exceeds these range
limits.

Upper Limit: 2.0
Lower Limit:

x

FREQ MULT

0.001 x

Upper Limit

Set up the generator as for continuous operation
(refer to paragraph 3.2.1). The frequency setting will
be the center frequency from which the modulated
signal will vary. Switch to internal or external FM
modulation. If internal, set the modulation generator
frequency as desired and sync on the modulation
generator signal. Set the modulation amplitude for the
amount of modulation desired. Because the main
generator is limited in

frequency

range (limited to ap­proximately the dial range for any given multiplier set­ting),

the

main generator frequency dial and the
modulation amplitude control. must be balanced to
stay within that range. The range is shown in figure 3-4
as the OUTPUT FREQUENCY FACTOR, which, when
multiplied by the FREQ MULT setting, gives the actual
output frequency. Example
swept

over the

full frequency range when the main

1

shows the output being

generator frequency dial is set at midpoint (1 .O), the

MOD AMPLITUDE control set at midrange and the
modulation signal is a balanced waveform

( 2/ , 2/
or \ ); that is, the modulation generator voltage
swings both positive and negative. If the MOD
AMPLITUDE control is rotated toward ccw, the
voltage swing decreases and the angle subtended in
the nomograph decreases. If the MOD AMPLITUDE
control is rotated toward MAX, the angle subtended
would overshoot the OUTPUT FREQUENCY FACTOR

range, indicating that saturation is likely.

Sweep Operation

3.2.7
For sweep operation, set up the generator for con-

tinuous operation (refer to paragraph 3.2.1). The fre­quency setting will be the lower frequency of the con­tinuously varying (or swept) frequency. Switch

FM/SWP
If

internal set the modulation generator FUNCTION

to internal or external modulation as desired.

2.0-

1.8.

1.6-

1.4-

.8-

.6-

.4-

.2-

.002-

Figure

*Multiply by FREQ MULT for actual output.

3-4.

Frequency Modulation Nomograph

.6

.8

1.6

1.8

switch to SWP SET, monitor the FUNCTION OUT with
a counter or oscilloscope and vary the MOD
AMPLITUDE control for exactly the upper frequency
desired. Note that the main generatoris limited in fre­quency range (limited to approximately the dial range
for any given multiplier setting). Select either/l/l for

sweep up
rate desired. Keep in mind

orM

for sweep down. Select the sweep

them andb

frequen­cies are double the indicated frequencies on the
FREQ/PERlOD

control.

Example 2 shows the output being swept from the
bottom of the range to midrange by setting the main
dial fully cw and the VERNIER fully ccw for absolute

bottom of the range. The MOD AMPLITUDE control

)

was left at midrange and the ramp

(/1/1

waveform
used as the modulator. The ramp is a positive going
only waveform. Had a balanced waveform been used,
the angle subtended would have included the dotted
line and resulted in saturation. If an external modula­tion signal is to be used, the EXT MOD IN values in the
nomograph indicate the signal level required for the
desired results.

3-5

3.1.2

Modulation

FUNCTION Switch

14

Generator

-

This switch selects the
waveform output of the modulation generator.
Output is at the OUT BNC connector
also available internally to the main generator.
Waveforms are sine
square

(N\).

AMPLITUDE

sweep frequency.

( ‘% ),

ramp up (M) and ramp down

A SWP SET detent holds the OUT BNC at

control 14 level;

( /L ),

triangle

used

to set upper

16

and is

( 2/ ),

.

AM- The instantaneous amplitude of the out-

d

put signal varies with the instantaneous ampli-

tude of the modulation signal.

e.

FM- The instantaneous frequency of the out­put signal varies with the instantaneous ampli­tude of the modulation signal.

f

.

PM- The instantaneous phase of the output
signal varies with the instantaneous amplitude of
the modulation signal.

MOD AMPLITUDE Control - This inner con­trol attenuates the modulation generator signal
that is internally fed to the main generator when
modulating. It has no effect during internal trig­gering or gating and it has no effect on the

16

OUT

FREQ/PERIOD

15

signal.

MULT Switch - This outer switch
(with ranges given in both frequency and period)
selects the modulation generator frequency/

period range.

-

VARIABLE Control

This inner control sets

the frequency/period within a range.

OUT

(6OOn)

16

Connector - This BNC is the

modulation generator waveform output: sine

( % ),

triangle

level

1OV p-p

balanced about ground and ramp

( 2/ )

and square

(5V p-p into

6OOQ)

waveforms

( ‘L )

fixed

( AA, M )

fixed level 0 to + 5 Vp waveform.
FM IN (5

17

kQ)

Connector - This BNC is

the input
for frequency modulation of the modulation
generator.

Sensitivity is 20% of frequency range

per volt in.

OPERATlON

32

.

convenience,

For

the generator operation has
been grouped in seven basic modes, from which
many variations and combinations are possible.
The following paragraphs give basic switch posi­tions for each mode and requirements and sug­gestions for operation.

.

g

3.2.1
When setting up the generator, it is advisable to

serve the output on an oscilloscope. Connect
TION

5OQ

-

The dc output can be set from + 15 Vdc

DC

- 15

to

Vdc (+ 7.5 Vdc to - 7.5 Vdc into

5OQ).

Continuous Operation

ob-

FUNC-

OUT to the scope input using a 500 cable and a

load. For continuous waveform output, select a
basic waveform at the desired frequency. Ensure the
modulation switches are set to OFF and the mode is
set to

CONT.

The output amplitude can be as great as

15V p.p;

attenuate as desired.

NOTE

use

For best waveform quality,
TENUATIO N
tion; then use

SWITC H

the

for gross attenua-

AMPLITUDE control for

the AT-

fine attenuation.

The waveform may be skewed to the left or right using
the SYMMETRY control; e.g., making a ramp
from a triangle

(

/G

.)

waveform.

( ,/1 )

/

NOTE

10

The output frequency is divided b y

when

the SYMMETRY control is switched from

the OFF position.

The dc level of the waveform may be varied with the

DC OFFSET control, but waveform clipping can occur.

NOTE

The basic modes of operation are:

a.

Continuous- A continuous output signal.

b

.

Triggered

-

One cycle of waveform for each

trigger signal.

C.

Gated

-

A “burst” of waveforms for the dura-

tion of each gate signal.

Waveform clipping will occur (OVERLOAD

LED will light), unless waveform amplitude

is decreased so

that

wavefor m

plus

offset

is less than 7.5 volts at the waveform peak.

3.2. 2

Triggered Operation

In triggered operation, there is one cycle of output for

each trigger signal input. For triggered operation, first

3-3

set up the generator for continuous operation (refer to
paragraph 3.2.1). The main generator may be trig-

gered internally by the modulation generator or trig-

gered by an external source. If an unmodulated
waveform is being output, the modulation generator is

free. to give the desired triggering frequency and

should be selected as the trigger source. Use any

modulation generator waveform as the trigger. Set the
modulation generator frequency for the desired trig­ger frequency and sync on the modulation generator
output.

NOT E

3.2.4

The TRIGGER LEVEL control
manually triggering or gating the generator. For

manually triggering (single cycles), the generator

mode should be EXT TRIG with no external signal in­put at the EXT TRIG IN connector. Each time TRIG­GER LEVEL is rotated cw through mid-position, one
triggered cycle will be generated. In EXT GATE mode,
the generator runs continuously as long as the TRIG­GER LEVEL is

Manual Triggering and Gating

can also be used

CW

of mid-position.

for

1. Trigger frequency must be slower than
the output waveform frequency.

2.

The MOD AMPLITUDE control has no
effect in

Rotate the TRIGGER LEVEL control to obtain a good
trigger. If the waveform start/stop point is to be other
than zero degrees, set the TRIG START/STOP control
as required. (See figure 3-3.) Haverwaves can be set

up using start/stop control and

-90°

s--

If external triggering is to be used, connect a repeti­tive signal with a positive going transition of greater

than one volt to EXT TRIG IN using a
the TRIGGER LEVEL control for proper triggering.

3.2. 3

In gated operation there is a “burst” of waveforms
lasting the duration of the gate pulse plus the time re-

quired to complete the last cycle of waveform started.

Set up as for triggered operation (refer to paragraph 3.2.2)
and select a “trigger” signal whose duty time gives
the desired waveform burst.

AA

Figure

Gated Operation

INT

TRIG

and INT GATE modes.

dc

offset control.

HAVERSINES

_v

3-3..

Waveform Start/Stop Examples

5OQ

cable. Adjust

3.2.5

AM Operation

In amplitude modulation, the instantaneous amplitude
of the output signal varies with the instantaneous
amplitude of the modulation signal.

NOT E

The output waveform will be
LOAD LED will light) if any instantaneous
amplitude greater tha n
( t

7.5 volts into

Set up the generator as for continuous operation
(refer to paragraph 3.2.1). Switch to internal or exter­nal amplitude modulation. If internal, note that the car-

rier (main generator waveform) mean amplitude is
decreased to half. This is to prevent clipping
driving the output amplifier) when the carrier ampli­tude is modulated (increased and decreased) by
another signal. Set the modulation generator fre­quency to a lower frequency than the main generator
and sync the scope to the modulation generator output.
Set the modulator amplitude for a desired percentage
of amplitude modulation (0 to greater than 1
and set the main generator ATTENUATION and
AMPLITUDE controls for a desired amplitude of
modulated waveform. If external modulation is
selected, observe that the carrier (main generator
waveform) amplitude drops to zero (null). This is for
suppressed carrier mode of amplitude modulation.
Connect the modulator OUT

IN with a coaxial cable. Set the main generator
ATTENUATION and AMPLITUDE controls
amplitude of suppressed carrier waveform. For best

results when using an external modulation signal at

EXT MOD IN, maintain as near as convenient
amplitude (which does not exceed 5
main generator ATTENUATION and AMPLITUDE con­trols. An external source may also be used for regular
AM operation, rather than suppressed carrier opera­tion, by supplying a dc component along with the ac

5OQ )

is produced.

clipped(OVER-

t

15 volt s

(6OOQ)

to the EXT MOD

VP);

(over-

00%

range)

for

a desired

a

5 Vp

then use the

3-4

modulating signal (observing 5 Vp limit) to set the car-

rier level.

MAIN DIAL

SETTING

AMPLlTUDE

MOD

MOD IN

EXT

OUTPUT

FREQUENCY

FACTOR*

FM Operation

3.2.6
In FM operation, the instantaneous frequency of the

output signal varies with the instantaneous amplitude
of the modulating signal.

NOTE

The

output

frequency modulation will not
be linear when the instantaneous
modulated frequency exceeds these range
limits.

Upper Limit: 2.0
Lower Limit:

x

FREQ MULT

0.001 x

Upper Limit

Set up the generator as for continuous operation
(refer to paragraph 3.2.1). The frequency setting will
be the center frequency from which the modulated
signal will vary. Switch to internal or external FM
modulation. If internal, set the modulation generator
frequency as desired and sync on the modulation
generator signal. Set the modulation amplitude for the
amount of modulation desired. Because the main
generator is limited in

frequency

range (limited to ap­proximately the dial range for any given multiplier set­ting),

the

main generator frequency dial and the
modulation amplitude control. must be balanced to
stay within that range. The range is shown in figure 3-4
as the OUTPUT FREQUENCY FACTOR, which, when
multiplied by the FREQ MULT setting, gives the actual
output frequency. Example
swept

over the

full frequency range when the main

1

shows the output being

generator frequency dial is set at midpoint (1 .O), the

MOD AMPLITUDE control set at midrange and the
modulation signal is a balanced waveform

( 2/ , 2/
or \ ); that is, the modulation generator voltage
swings both positive and negative. If the MOD
AMPLITUDE control is rotated toward ccw, the
voltage swing decreases and the angle subtended in
the nomograph decreases. If the MOD AMPLITUDE
control is rotated toward MAX, the angle subtended
would overshoot the OUTPUT FREQUENCY FACTOR

range, indicating that saturation is likely.

Sweep Operation

3.2.7
For sweep operation, set up the generator for con-

tinuous operation (refer to paragraph 3.2.1). The fre­quency setting will be the lower frequency of the con­tinuously varying (or swept) frequency. Switch

FM/SWP
If

internal set the modulation generator FUNCTION

to internal or external modulation as desired.

2.0-

1.8.

1.6-

1.4-

.8-

.6-

.4-

.2-

.002-

Figure

*Multiply by FREQ MULT for actual output.

3-4.

Frequency Modulation Nomograph

.6

.8

1.6

1.8

switch to SWP SET, monitor the FUNCTION OUT with
a counter or oscilloscope and vary the MOD
AMPLITUDE control for exactly the upper frequency
desired. Note that the main generatoris limited in fre­quency range (limited to approximately the dial range
for any given multiplier setting). Select either/l/l for

sweep up
rate desired. Keep in mind

orM

for sweep down. Select the sweep

them andb

frequen­cies are double the indicated frequencies on the
FREQ/PERlOD

control.

Example 2 shows the output being swept from the
bottom of the range to midrange by setting the main
dial fully cw and the VERNIER fully ccw for absolute

bottom of the range. The MOD AMPLITUDE control

)

was left at midrange and the ramp

(/1/1

waveform
used as the modulator. The ramp is a positive going
only waveform. Had a balanced waveform been used,
the angle subtended would have included the dotted
line and resulted in saturation. If an external modula­tion signal is to be used, the EXT MOD IN values in the
nomograph indicate the signal level required for the
desired results.

3-5

3.2.8 PM Operation

In PM operation, the instantaneous phase of the out­put signal varies with the instantaneous change in
amplitude of the modulating signal. The change in
phase
generator until the correct phase angle change is

made. The modulation circuit differentiates the modu­lation signal; that is, its output is proportional to the

rate of change of modulation signal amplitude. This
voltage is fed to the ‘main’ generator in exactly the
same manner‘as the FM voltage is. The voltage effects
a change in frequency and, in the case of a step func­tion modulation, for example, exists only long enough
to cause the desired phase shift. Typically, less than
one cycle is required to change the phase. When the
phase angle is increased, the frequency increases to
achieve it. When the phase angle is decreased, the
frequency decreases to achieve it. The frequency re­quired to change the phase also depends upon the
modulation frequency and waveform.

Nominally, the phase of the main generator is shifted
ten degrees for each volt of instantaneous modulation

is

made by changing the frequency of the

NOTE

The output phase will not be linearly modu-

lated

wh

en the instantaneous transition fre­quencies required to effect the phase
change exceed these range limits.

Upper Limit: 2.0
Lower Limit: 0.001

x

FREQ

MULT

X Upper

Limit

signal. When the main generator is set above a range

midpoint, the modulation signal begins to lose its ef­fectiveness. The effect is that the input signal is rolling
off at 6 dB/octave due to form factor limitations of the

input differentiator. This effect also occurs for
modulation signal frequencies above 150

Set up the generator as for continuous operation
(refer

to

paragraph 3.2.1). Select a range so that the
frequency dial can be set, at midpoint or below (for
linear operation) and switch to internal or external
phase modulation.

NOTE

There is no PM operation for frequency

multipliers of 100 or less.

If internal, set the modulation frequency as desired. (If

other than sine waveform is selected, greater than

150

kHz

modulation frequencies are possible and the
effective roll off must be considered.) Set the modula­tion amplitude as desired. Full range is 5 Vp and
phase shift is

Because the initial phase reference no
longer exists when the phase shifts, phase
shift measurement will not be possible with
an oscilloscope alone. To measure the

phase shift, an additional circuit

phase modulator will be necessary to

establish a phase angle baseline.

10°

per 1 Vp.

NOTE

kHz.

such as

a

3-6

4.1 FUNCTIONAL BLOCK DIAGRAM ANALYSIS

This

section describes the functions of major circuit
elements and their relationship to one another as
shown in figure 4-1, functional block diagram, and
figure 4-2, basic generator and timing diagram.
Paragraph
circuit

As shown in figure 4-1, the main generator VCG

(Voltage

amplifier receives inputs from the frequency dial, ver­nier, FM and PM switches which produce a sum cur-

rent. The PM input is provided with a passive differen-

tiator which produces a voltage proportional to the

rate of change of the instantaneous voltage of the

modulating signal.
The VCG summing amplifier is an inverting amplifier

whose output voltage is used to control a complemen­tary current source and current sink. For symmetrical
output waveforms, the currents are equal and directly
proportional to the algebraic sum of the VCG inputs.
The diode gate, controlled by the hysteresis switch,
switches either the current source or sink to the timing

capacitor selected by the frequency multiplier con-

trol. When the current source is switched in, the

charge
the positive-going triangle slope. Likewise, the current
sink produces the negative-going triangle slope.

The triangle amplifier is a unity gain amplifier whose

output is fed to the hysteresis switch and to the
triangle buffer. The hysteresis switch is a bistable
device operating as a window detector with limit
points set to the triangle peaks. When the hysteresis
switch output is +
limit, and the hysteresis switch goes to - 2V. This
switches currents at the diode gate and the negative­going
reaches the
switch back to positive, repeating the process. As
shown in figure 4-2, this repetitive process results in
the simultaneous generation of a square wave and a
triangle wave at the same frequency.

4.2

provides further descriptions relating

blocks

on the capacitor will rise linearly producing

triangle slope is started. When the triangle

to schematics in section 7.

Control of Generator frequency) summing

2V,

- 1.25V

the triangle rises to the +

limit, the hysteresis switch will

1.25V

selector and by the magnitude of the currents sup­plied to and removed from it. Since the currents are
linearly proportional to the sum of VCG inputs, so will

be the output frequency. The capacitance multiplier

provides the bottom four frequency ranges.

When the variable symmetry control is rotated, it first

reduces the current sink by a factor of 19, making the
negative-going triangle slope 19 times longer than

normal. This results in an unsymmetrical waveform
output and a frequency division by IO. Continued rota­tion gradually increases the current sink and reduces
the current source in such a way that the period for
the triangle to complete one cycle remains constant.
This action produces continuously variable symmetry
of the output waveforms over a
while frequency remains constant at one-tenth of dial
and multiplier settings.

The inverted square from the hysteresis switch is fed
to the sync amplifier, where it is buffered and con­verted to a TTL level output, and to the square
amplifier, where (if square or pulse functions are
selected) a buffered square is sent to the signal

shaper for conditioning.
The triangle buffer provides the

cient drive for the signal shaper and presents a small,
constant load on the triangle amplifier.

, HYSTERESIS

.

C

A

-

1:19

to

$_

1.25 triangle suffi-

I

SWITCH

*

19:1

range

6

The output frequency is determined by the magnitude
of the capacitor selected by the frequency multiplier

Figure

4-2.

Basic Generator Block

and Timing Diagram

4-l

The signal shaper contains switching elements and a
diode array for signal conditioning the buffered
triangle and square inputs into the various waveforms
controlled by the function switch. The selected
waveform is the carrier (+ Y) input to the transcon­ductance multiplier,

an integrated circuit,

four-

quadrant multiplier.
The modulation (+X) input is a positive dc from the

control

amplifier when the

AM switch

is off, providing
a fixed gain reference for the multiplier. Output cur­rents from the multiplier are applied to the summing
node of the preamplifier for conversion to an inverted
voltage signal.

The preamplifier output is then attenuated by the front
panel amplitude control and fed to the output amplifier
summing node along with the dc offset control. The
output amplifier is an inverting amplifier whose output
is fed into step attenuator and then to the function
output connector.
distributed network having
This network provides attenuation in 20 dB
steps to 60

dB.

The attenuator consists of a

5Oa

output impedance.

(1/1

0)

For continuous operation of the basic function
generator loop (bold path in figure 4-1), the trigger
amplifier must maintain a positive level above the
most positive charge on the

integrating

capacitor in
order to reverse bias the start/stop diode. Thus, in
continuous mode the trigger logic senses the con­tinuous control line from the front panel mode selec­tor and holds the inverting trigger amplifier input low.

In triggered and gated modes the trigger amplifier out­puts some level below the positive peak charging
level, and the start/stop diode is forward biased to
sink the current source and prevent the timing
capacitor from charging to the positive peak. This
stops waveform generation and holds the triangle out­put at some dc level called the trigger baseline. The
trigger baseline is the level where a triangle, and thus
sine, waveform starts and stops when triggered or
gated.

The normal trigger baseline is zero volts, analogous to

0°

phase of a sine or triangle waveform. The trigger
start/stop control offsets the trigger amplifier output
and can change the baseline for starting and stopping
a sine or triangle waveform from its negative peak

(- 90°)

to its positive peak (+

90°)

At the extreme

positive peak level setting though, the diode is again

reverse biased and generator operation goes con-

tinuous, independent of generator mode.

While the integrating capacitor is being held from
charging, the start/stop diode must sink the current
source, which has a magnitude variable with VCG in­puts. Therefore, a compensation is necessary to the
voltage level output by the trigger amplifier in order to
maintain a constant baseline level as VCG inputs, cur-

rent source magnitude and forward voltage drop by
the start/stop diode are varied. The baseline compen­sation circuit measures the forward voltage across a
diode placed in the current source and injects an off­setting current into the trigger amplifier to maintain an
equal voltage differential between the baseline level
and trigger amplifier output.

The trigger logic determines that after a waveform
starts, it always stops at a complete cycle and at the
same phase angle at which it started. The trigger logic

receives a trigger stimulus from the signal limiter and

latches the trigger amplifier output positive, allowing
the generator loop to run. When the negative peak of
the last cycle is reached (just one cycle in trigger
mode), the square from the hysteresis switch latches
the trigger amplifier back to its previous level. The in­tegrating capacitor will charge back to the trigger
baseline

where the start/stop diode once again for-

ward biases.

The generator mode switch sets the gated control line
to determine whether the trigger logic is to latch the
generator on for one cycle of for the duration of the
trigger stimulus.

The modulation generator board contains the power
supplies, the modulation generator and various
switching elements to control the source and type of

modulation and triggering signals to the main

generator.

The modulation generator is an integrated circuit
source of sine, triangle and square waveforms, whose
frequency is controllable by front panel multiplier
switch, variable control, and external voltage at the

FM IN input. The triangle and square are applied to a
ramp generator consisting of a balanced modulator

and buffer amplifier to produce ramp waveforms. A

modulation waveform or a SWP SET dc level is sent to
the function buffer via the front panel function selec­tor.

The function buffer output is sent to the modulation

output

(6OOQ)

connector, the generator mode switch
for an internal trigger and gate stimulus, and the
amplitude buffer after being attenuated by the front
panel amplitude control. The amplitude buffer output
goes to the AM, FM and PM switches “internal” posi­tions. The EXT MOD IN connector provides a

connec-

4-2

tion for an external signal to the switches “external”
positions.

The FM and PM switches provide VCG inputs. The AM
switch controls the control amplifier and thus the
transconductance multiplier. When AM is off, the con­trol amplifier produces a positive dc level giving the
multiplier a fixed gain. With internal AM, the dc com­ponent from the control amplifier is cut in half, halving
the output amplitude to prevent output clipping when
modulating. The selected

modulation

waveform rides
on the dc. The ac (modulation signal) has a peak value
equal in magnitude to the dc level when the modula­tion amplitude control is maximum, making the sum of
modulator and carrier signals equal to the maximum
output capability of the output amplifier, and the differ­ence equal to the zero output level, which is

100%
modulation. Then, by varying the modulation signal, a
variable 0 to 100% AM of the carrier (main generator)
signal is produced. With external AM, the dc compo­nent is switched to 0 Vdc, resulting in zero amplitude
output, and bipolar signal inputs at the EXT MOD IN
connector will produce suppressed

carrier (4-quadrant)

modulation.

4.2

CIRCUIT ANALYSIS

4.2.1 VCG Amplifier

across series resistors to the supplies equal to the
control voltages. The FET currents will be switched at
the diode gate into a timing capacitor to produce the
triangle waveform.

4.2.2

Symmetry Control

Let the source of Q2 be - 5 Vdc, the wiper of the sym-

-

metry control,

2.5 Vdc, and the source of
The output of U3 will have no current, each
tor will have

1 mA,

and generator frequency will be at

Q1,

R/2

0 Vdc.

resis-

maximum of the range. Open the symmetry switch
and set the potentiometer to its electrical center. The
output of U3 is still at an equipotential point, but now
the total resistance with 5 Vdc across it has changed
from

R

to

10R.

Thus, current will drop to 100 PA and
output frequency will drop to one-tenth of range. If the
potentiometer is rotated, current will flow in U3 output
to maintain the wiper at

-

2.5 Vdc. When the potentio-

meter is ccw, the wiper is at the positive direction and
the upper R/2 will have
source of
which puts

1 mA.

But the lower R/2 is in series with

2.5V

across 19 x the normal resistance.

2.5V

across it with a current

9R,

Now the current sink will have one-nineteenth the
magnitude of the current source. The output waveform
for this condition is shown in figure 4-3. Regardless of
where the symmetry control is rotated, frequency
stays the same (one-tenth of range).

Figure 4-3 is a simplified schematic of the VCG cir­cuitry. The value of a resistor

“R”

is 5 kQ and supplies
are t 15 Vdc. U1 is connected as a summing
amplifier to sum the VCG inputs. A top of range input
produces 1
in

-

5 Vdc at the output of

mA

through the feedback resistor resulting

U1

The negative input of U4 is held at the output level of

U1 by controlling the current through
back. One half the output of U1 is buffered by

Q2

as a feed-

U3

and
applied to the wiper of the variable symmetry control.
The negative input of

U2

is held at 0 Vdc by controlling
the current through Ql as a feedback. As long as the
variable symmetry control is off, the two R/2 resistors
have equal voltage across them and an equal current
through them as through U1 feedback and there is no
current at the output of U3. Since an equal current
exists in the entire resistor string from + to

-

supply,
the result is a positive control voltage relative to the
negative supply at U6 + input and a negative control
voltage

with respect to the positive supply at U5 + in­put, each of which is proportional to the sum of the in­puts to

U1

Similarly, U5 and U6 establish feedback by regulating
current through

FETs,

producing a voltage drop

4.2.3

Range Switching

For frequency ranges associated with multiplier posi-

tions of 100 and

1

K, main board schematic, sheet 1,

the value of the current source and current sink setting

resistors R326, R38, R48 and R330 is 5

kQ,

which pro­vides integrating current sensitivity of 200 PA per volt
of external FM input. With the timing capacitors of 1
and 0.1

pF,

plus the bulk of the top range timing capa­citor and the stray capacitance of the multiplier switch,
the generator produces the calibrated output fre­quency for these ranges. In the top range (multiplier
position of

10M),

the current setting resistors are
paralleled with resistors of one-ninth the value, caus­ing both current sources to run at ten times the usual
current, resulting in 2
When this current is used with the nominal -90

mA

per volt of external FM input.

pF
timing capacitor (fixed value plus strays), the top
range of frequencies result. For the next three ranges
down (multiplier positions

1

M,

100K, 10K),

the nominal
timing capacitor is the fixed top range capacitor plus
strays (i.e.,

910

pF,

0.01

pF).

capacitors of 101

plus the switched values (11

These result in joint timing

pF,

1010 pF and 0.0101

,uF.

pF,

In these

-90

pF)

three ranges the positive and negative current
sources are boosted by 1

%

over the next range down

4-3

VERNIER

+

R/9

OM

I

1

R/2

1

R

v

SYMMETRY

R

R/2

z

Figure 4-3. VCG Simplified Schematic

-

R/9

(multiplier 1 K) by switching 500
with the 5

R38, R48 and R330 producing the output frequencies
for these ranges. The four ranges below multiplier set­ting 100 all have the same integrating current and tim­ing capacitor as the 100 multiplier range, but for each
of these ranges, 90%, 99%, 99.9% and 99.99% of
the integrating current is subtracted by the
capacitance multiplier circuit.

4.2.4

For the frequency ranges associated with multiplier
positions of
circuit (main board schematic, sheet I), senses the
timing capacitor charging current and subtracts the
appropriate amount so that the effective charging cur­rent is a fraction of that delivered by the current
sources. This is accomplished by the connection of

the capacitance multiplier to the timing capacitor with
one input-output terminal through a section of the fre­quency multiplier switch. The + terminals of U7 and

U8 serve as potentiometric input to these amplifiers.
U7 has a fixed resistive feedback network, giving it a

fixed gain. Capacitor C26 is forced to comply to the
triangle voltage wave being generated, because the

R54

side is driven at the potential of the input/output
terminal and the other side has the same waveform
with some fixed gain from U7. Since the side driven at
the input/output signal is a summing node, it is fed the
necessary

R59, R60 and
selected by the frequency multiplier control, taking on
values which give the correct amplitude to the output
of U8. This output with respect to common is

input/output waveform with a square wave super-

imposed;
be picked up for signal tracing. The input/output wave­form is a triangle wave so the differential across
and R63 is a square wave with the correct amplitude
to subtract part of the timing capacitor charging cur-

rent. Since this square wave amplitude is controlled in
decades by the frequency multiplier control via R58,

R59,

R60 and
in decades even though the current sources and tim­ing capacitor remain the same.

kS2

basic current setting resistors

Capacitance

10

current by the feedback resistors

TP1

is the test point where this output can

R61,

Multiplier

through 0.01, a capacitance multiplier

R61.

The feedback resistors are

the instrument frequency is divided

kS2

resistors in parallel

R326,

R58,

the-

R62

a matched duplicate FET,
drain current as Q8 and, therefore, the same

source voltage. In series with Q10 is a duplicate emit-

ter follower,

rent as
base voltage. Since the gate of the dummy FET,
connected to the emitter of the dummy emitter
follower,
voltage. Therefore, within the tolerances of the part
parameters and some unaccounted error for base
current, the active emitter follower output voltage will
be at the value of the input gate. The remaining tran­sistor,
dynamic lead networks at the input of the hysteresis
switch. In this role, it needs no dc integrity, as the out­put is not directly coupled.

4.2.6

Hysteresis Switch

The hysteresis switch (main board schematic, sheet 2)
consists mainly of
and

Q14/Q15,
of U14 compares an input voltage to common. The in­put network provides a positive bias to one and a
negative bias to the other; therefore, when the input
terminal (output of the triangle amplifier) is at
the flip-flop changes state. The flip-flop selects which
input comparator of the hysteresis switch will be ac­tivated in preparation for the next change of state.
When the timing capacitor is integrating positively,
the positive biased comparator is activated. When the
timing capacitor voltage reaches +
changes state, the negative comparator is activated
and the direction of integration is reversed, so that

when the timing capacitor signal reaches

the flip-flop switches back and the cycle starts over.
In addition to the positive and negative biases at the
comparator inputs, there is a dynamic lead network

on each one. These lead networks are driven by

a separate emitter follower, from the triangle ampli-

fier. They provide the necessary lead to compensate
for the inherent delays of the hysteresis switch,
thereby keeping the higher frequency dial nonlinearity
and sine distortion to a minimum.

4.2.7

Q13. Q13

Q10;

therefore, it has the same

Q13,

the two terminals have the same

Qll,

is a second emitter follower for driving the

U14,

an output flip-flop. Each differential pair

Diode Gate and Timing Capacitor

Q9. Q9

has the identical collector cur-

a double input comparator,

has the identical

gate-to-

emitter-to-

Q9,

is

t 1.25V,

1.25V,

the flip-flop

- 1.25V,

Q11,

4.2.5

Triangle Amplifier

The main board schematic, sheet 2, shows the

amplifier; it uses
Q10,

a bipolar emitter follower, for an open

of

one. It is a fast, very high input impedance circuit
with output impedance low enough to drive the hyster­esis switch and the triangle buffer. In series with

Q8,

an FET source follower, to drive

triangle

loop gain

Q8

is

The diode gate (current switch) and the timing
capacitor circuits are shown in the main board
schematic, sheet 2. The current source and sink are
switched to the timing capacitor by the hysteresis
switch via a diode bridge arrangement called the
diode gate. Actually, the hysteresis switch is linked to
the bridge network by two emitter followers,
Q25,

with independent outputs biased to be at the

Q24

and

4-5

same voltage.
lustrated in figure 4-2 shows these points as one ter­minal at C. When the hysteresis switch output is
positive, CR16 is forward biased, so that the current
sink is sourced by the drive circuit and is ineffective.
CR1

3 and CR1 5 are reverse biased, providing isolation

between the drive circuit and the timing capacitor.

This leaves CR14 forward biased and free to conduct

the current source output to the timing capacitor.
When the timing capacitor voltage rises to the hys­teresis switch point
output switches low, forward biasing CR13 which
back biases
be isolated and the sink to discharge the timing capa­citor through CR15 This state continues until the

negative switch point is reached and reverts to the
previous state.

4.2.8 Triangle Buffer
The triangle buffer (main board schematic, sheet 2) is

a wide band dc amplifier providing a closed loop gain
of one in potentiometric connection. The input dif­ferential stage,
emitters are fed from a current sink
collector load, Q20, is a current source providing
greater open loop gain than a resistive load. Following
this is an emitter follower,
shifter, CR1 2, and another emitter follower, Q22, for
the

output stage. The gain is set to one by the 100%. .

feedback to the input pair feedback side, base of

4.2.9 Signal Shaper

The signal shaper circuit (main board schematic,

sheet 3) is uniquely set’up for each different waveform
by four wafers of the function selector switch. The

t

15 volt power is switched off in the triangle wave
mode and there is virtually no effect on the triangle
wave fed to the circuit. In the positive pulse mode, the
square wave, rather than the triangle wave, is fed to
the circuit and the
a result, the negative swing of the input square wave
is clipped off. The negative pulse is formed, when
selected by the function switch, in a similar manner.
When the square or sine wave is selected, both plus
and minus 15 volt power is applied to the circuit. The
difference in circuit setup for sine and square is the
resistive load at the circuit output and the shape of the
signal fed to the input. For the sine wave mode, the
matched set of -diodes soft clip the input triangle at
three different levels. These signals are resistively
summed to produce a sine wave voltage input to the
multiplier.
square wave is symmetrically hard-clipped by the

The simplified timing diagram il-

(+ 1.25V),

CR14

and CR16 and allows the source to

Q17/Ql8,

-

15 volt power is switched off. As

For the square wave mode, the input

the hysteresis switch

is a monolithic pair. The

Q19.

The active

Q21,

a

zener

diode level

Ql8.

diode network presenting a square wave input voltage
to the multiplier.

4.2.10

Transconductance Multiplier

After the main generator signal passes through the
function selector switch and the signal shaper circuit,

it enters a transconductance multiplier,
board schematic, sheet
by dc from the control amplifier or modulated by ac
from the modulation generator via the AM switch. Cur-

rents in the open collectors of this
a current mirror for optimum gain and fed to the pre­amplifier summing node for conversion to a voltage
signal at TP7.

4.2.11 Preamplifier
The preamplifier (main board schematic, sheet

the output (power) amplifier, is comprised of a high
frequency ac amplifier combined with a low frequency
dc amplifier. It converts the current from the multiplier
to a voltage signal which is attenuated by the front
panel amplitude control and amplified by the output
amplifier. The

remaining circuitry is the high frequency amplifier.

Again, like the output amplifier, the ac amplifier

symmetrically arranged from the
node to R246 and R249 at the output stage of the
preamplifier. If the input current goes into the node,
the voltage at the summing node will rise by a certain
amount. By capacitive coupling via C92 and C93, the
base voltage of Q40 rises closer to + 15 volts and the
base voltage of
volts. Thus, the emitter base junction of Q40 will be
less forward biased, thereby reducing the emitter cur­rent, while the Q41 ‘emitter current increases. The
result is an increase in current in Q42 and a decrease
in current in Q43, causing a decreased voltage output
in

R246/R249.The

summing node tends to cancel the rise in voltage
there, causing the output voltage to stabilize. The
amount of negative voltage at the output required to

pull the summing node back to zero is determined by

the value of R240.

4.2.12 Output
The output amplifier is comprised of a low frequency

dc amplifier and a high frequency ac amplifier. Refer
to the simplified circuit of figure 4-4. The
and Q38 circuit is the dc amplifier and the remaining
circuitry is the ac amplifier. The ac amplifier is sym­metrically arranged, top and bottom. The upper

U17

Amplifier

3),

where the amplitude is set

IC

circuit is the dc amplifier and the

R240/R238 summing

Q41

rises further away from - 15

feedback path through R240 to the

U15

(main

are worked into

3),

like

is

U19,

Q37

por-

4-6

tion amplifies the positive swing of the output, while
the lower mirror portion amplifies the negative swing.
Operation is class AB; that is, there is independent
positive half and negative half amplification, with a
small amount of current flow in both sides near zero

swing. The amplifier schematic has been simplified in

figure 4-4 for the following discussion. Assume that
both the input and the output voltages are zero, then
the voltage at point A should also be zero. Because of
the symmetrical configuration of the amplifier, the
current through
output will remain at zero.
the voltage at point A will rise by a certain amount.
This will cause the base voltage of Q47 to
to + 24 volts. Thus, the emitter base junction of Q47
will be less forward biased, thereby reducing its emit­ter current. The result is that the voltage at point B

Q47

and Q49 will be equal and the

If

the input goes positive,

rise

closer

which is the output voltage, will start to go negative.

Finally, when the output has moved far enough
negative to pull point A back to zero, by pulling current
through the feedback resistor Rfb, the collector cur­rent of Q47 and Q49 will again be equal and the output

voltage at point B will stabilize. The amount of nega-

tive voltage at the output required to pull point A back

to zero is controlled by the ratio of

ratio is the closed loop gain of the output amplifier.
The circuit containing
low frequency amplifier used to bias the high frequen-

cy amplifier and to increase the low frequency loop

gain. The high frequency amplifier is isolated from low

frequency signals at the input by capacitance coupl-

ing to the bases of

low frequency amplifier to bias the emitter of

obtain the required dc stability and high loop gain.

U19,

Q37, Q38 is a high gain,

Q47

and Q49. It then employs the

Rfb

to Rin, and this

Q47

to

INPUT 0’

U

19/Q37/Q38

+ 24 Vdc

r

Rin

+

_A

OUTPUT

Figure

- 24

4-4.

Simplified Output Amplifier

I

Vdc

4-7

Other circuit components are shown on the main
board schematic, sheet 3. Emitter followers Q46 and
Q48 increase the driving power to the bases of Q47
and Q49.
the load through R287 and
signalswing. Q51 and Q54 are driven by the collector
of Q47. CR40 through CR43 compensate for the
emitter-base junction voltage drops of
and Q55 to control idling current, reduce crossover
distortion and prevent thermal runaway. The two

resistor-capacitor networks,
R278/C101
high frequency amplifier gain during the transition
time prior to the dc amplifier taking effect. This im­proves the rise time, since the dc amplifier requires a
few microseconds to respond and stabilize. VR2 and
VR3 are five volt regulators which normally run
saturated to supply the output stage current to the col-

lectors of the output transistors. If the output stage
should demand an abnormal amount of current
through a shorted’transistor or output terminal, the
current through R295 through R298 will generate five
volts of drop. If more current is demanded, the

regulators will simply maintain the five volt drop,
allowing the output collector voltages to collapse,
preventing
amplifier components. The dc offset is fed as a cur-

rent from the front panel control to the output

amplifier summing mode.

4.2.13
The side of the hysteresis switch (main board sche-

matic, sheet 2) not used to drive the current switch
has an inverted square signal which is used to drive
an emitter coupled pair,
output of Q23 is biased to provide a TTL level output,
The sync out signal is connected to the front panel
sync out (TTL) BNC with a coaxial cable.

Next to the sync amplifier, a similar emitter coupled
pair, Q57 and Q58, is connected to the same input
and biased to output a bipolar square wave to the
function switch when square or pulse functions are
selected. In other functions, emitter bias is reversed
so that the square function remains confined to the
hysteresis switch area.

4.2.14
Either an external signal or the modulator function are

selected by the generator mode switch (auxiliary
generator schematic) and summed through R50 and
R51

with the trigger level control. That portion of the

trigger signal more positive than the trigger level is

Q51

and Q54 are a harnessed pair sharing

R291

during the positive

Q51,

Q53, Q54

R268/C1

are emitter bypass circuits to maintain the

excessive power dissipation

Sync Amplifier/Square Amplifier

Q16

and Q23. The collector

Trigger Signal Limiter

00 and

in the

clipped by forward biasing
is clipped by CR2. While

Q3

switches off to a TTL low level. While CR2 is on,
is off and Q3 saturates to a
R58 provide hysteresis to ensure a clean square wave
output.

4.2.15

In continuous mode the continuous control line is low
and
trigger flip-flop (U12) cleared.
sent by emitter follower Q27 to a diode “AND”. A low
is sensed at RI 58, the trigger amplifier inverting input.
The closed loop gain of the trigger amplifier is set by
the ratio of
puts a + 1.5 to + 2 Vdc to reverse bias the start/stop
diode CR27 above the most positive charge on the in­tegrating capacitor.

In trigger mode, both control lines are high, and U13
produces a narrow negative pulse, corresponding to a
high to low transition of the signal limiter output, to
clear
clocked by the negative-going edge of the current
switch
goes high and the trigger amplifier goes to a low level,

forward biasing CR27 which sinks the VCG current
source away from the
charge level on the
voltage drop across CR27 above the trigger amplifier
output. Compensation current enters the trigger
amplifier summing node through

put voltage down exactly the same as the drop
CR27 at a particular magnitude of integrating current.
The 0 Vdc trigger baseline may be modified with
the front panel start/stop control. Whenever a trigger

is received, U13 is cleared and the trigger amplifier
output goes high, allowing the integrating capacitor to
charge. At the positive triangle peak, the hysteresis
switch goes to a negative level and the negative-going
triangle slope is generated. The high-to-low hysteresis
transition clocks
of the square is also fed into the diode “AND” at
CR20 which holds the trigger amplifier output high un­til the completion of the negative-going slope of the
triangle. When the hysteresis switch returns to
positive, the trigger amplifier returns to its low output,
and the integrating capacitor charges until CR27 for­ward biases again. The integrating capacitor is again
held at the trigger baseline level.

In gate mode, the gated control line is low and

produces a negative pulse of the same duration as the

signal limiter output. Thus,

Trigger Logic/Trigger Amplifier

U13-8

(main board schematic, sheet 2) holds the

R173

to R158. The trigger amplifier out-

U12.

In the absence of a trigger stimulus,

square

translated by Q26 to TTL levels.

integrating

U12-3

CR1;

the negative portion

CR1

is on, Q1 conducts and

Q1

TTL

high level. R57 and

U12-3

is low, which is

U12

is

U12-3

integrating capacitor. The

capacitor is held at the

R155

to push its out-

across

R4,

high, but the negative portion

U13

U12

is held cleared, the

4-8

signal at CR24 is held low, and the trigger amplifier
output is held high for the trigger duration. The last
triangle cycle started is completed through the action
explained in trigger mode.

the start/stop diode are matched and carry equal cur-

rents, the trigger baseline will be stable with varying

VCG inputs.

4.2.16 Baseline
CR2 (main board schematic, sheet

the current supplied by the VCG current source.

Compensation

1)

is in series with

U9-3
is connected to CR2 anode and, since it is a voltage
follower, it will have the same potential at its pin 6.

U1 O-3 is connected to CR2 cathode and will regulate

the current through

Q7

to make the same potential at
its pin 2; therefore, R64 will have the same voltage
across it as the drop across CR2. The current leaving

Q7

enters the trigger amplifier summing node, and

becomes a voltage offset equal to the drop across

CR2, because R64 and the feedback resistor for the
trigger amplifier have the same value. Since CR2 and

4.2.17

Modulation Generator and Ramp Generator

The function generator used as a modulation source

in the instrument is the lntersil 8038 (U2 on the auxil­iary generator board schematic). It is fitted with an
auxiliary current balancing circuit

(U1)

to extend its
useful dynamic range. The ramp output which is not
built into the chip is developed by amplitude
modulating the triangle function with the square func-

tion in a balanced modulator
(

2/

, 2/ ,

‘1_1

,

M,

(U5).

The output signals

M )

are selected in a
function selector switch and fed to the modulation
switches where modulation type is selected. The

ramp signals have a fundamental frequency of two

times that of the other waveforms.

4-9