Stanford Research Systems DS345 User Manual
30 MHz Synthesized
Function and Arbitrary
Waveform Generator
model DS345
1290 D Reamwood Avenue
Sunnyvale, CA 94089 USA
Phone: (408) 744-9040 • Fax: (408) 744-9049
www.thinkSRS.com • e-mail: info@thinkSRS.com
Copyright©1999
All Rights Reserved
Revision 1.6 • 10/99
Stanford Research Systems
Table of Contents
Condensed Information
Safety and Use
v
Specifications
vii
Abridged Command List
xi
Getting Started
Introduction
1-1
CW Function Generation
1-1
Frequency Sweep
1-2
Tone Bursts
1-3
Operation
Introduction to DDS
2-1
DS345 Features
2-5
Front Panel Features
2-5
Rear Panel Features
2-7
Function Setting
2-9
Setting the Function
2-10
Frequency
2-10
Amplitude
2-11
DC Offset
2-12
Phase
2-12
Sweeps and Modulation
2-13
Modulation Parameters
2-13
Modulation On/Off
2-13
Modulation Type
2-13
Modulation Rate
2-14
Amplitude Modulation
2-15
External AM
2-15
Internal AM
2-15
Frequency Modulation
2-16
Phase Modulation
2-17
Burst Modulation
2-18
Burst Count
2-18
Starting Point
2-18
Frequency Sweeps
2-19
Sweep Type
2-19
Sweep Frequencies
2-19
Sweep Markers
2-20
Sweep Outputs
2-21
Trigger Generator
2-22
Arbitrary Modulation Patterns
2-23
Pulse Generation
2-24
Instrument Setup
2-25
Default Settings
2-25
Store and Recall
2-25
GPIB and RS232 Setup
2-26
Self-Test and Autocal
2-27
Arbitrary Waveform Editing
2-29
Edit Menu
2-29
Point Format Editing
2-30
Point Format Example
2-31
Vector Format Editing
2-32
Vector Format Example
2-33
Programming
Programming the DS345
3-1
Communications
3-1
GPIB Communication
3-1
RS-232 Communication
3-1
Data Window
3-1
Command Syntax
3-1
Detailed Command List
3-3
Function Output Commands
3-3
Modulation Control
3-4
Arb Waveform and Modulation
3-6
Setup Control Commands
3-9
Status Reporting Commands
3-9
Test and Calibration Commands
3-10
Status Byte Definitions
3-12
Programming Examples
3-15
Arbitrary AM Modulation
3-16
Arbitrary FM Modulation
3-17
Arbitrary PM Modulation
3-18
Point Mode Arb Waveform
3-19
Vector Mode Arb Waveform
3-20
Test and Calibration
Troubleshooting
4-1
Operation Error Messages
4-1
Self-Test Error Messages
4-3
Autocal Error Messages
4-4
i
DS345 SYNTHESIZED FUNCTION GENERATOR
DS345 SYNTHESIZED FUNCTION GENERATOR
Performance Tests
5-1
Necessary Equipment
5-1
Functional Tests
5-2
Front Panel Test
5-2
Self Tests
5-2
Sine Wave
5-2
Square Wave
5-2
Amplitude Flatness
5-3
Output Level
5-3
Performance Tests
5-5
Frequency Accuracy
5-5
Amplitude Accuracy
5-5
DC Offset Accuracy
5-7
Subharmonics
5-7
Spurious Signals
5-8
Harmonic Distortion
5-8
Phase Noise
5-9
Square Wave Rise Time
5-10
Square Wave Symmetry
5-10
AM Envelope Distortion
5-10
Test Scorecard
5-11
Calibration
6-1
Introduction
6-1
Calibration Enable
6-1
Calbytes
6-1
Necessary Equipment
6-3
Adjustments
6-3
Clock Adjustment
6-3
DAC Reference Voltage
6-4
Output Amplifier Bandwidth
6-4
Bessel Filter Adjustment
6-4
Harmonic Distortion
6-5
Calibration
6-6
5.00 V Reference
6-6
Clock Calibration
6-6
Attenuator Calibration
6-6
Carrier Null Calibration
6-7
Sinewave Amplitude
6-8
Square Wave Amplitude
6-8
Square Wave Symmetry
6-9
Arbitrary Waveform Software
Introduction
7-1
Getting Started with AWC
7-1
Hardware Requirements
7-3
Menus
7-3
File Menu
7-3
Edit Menu
7-3
Waveform Menu
7-4
Send Data Menu
7-5
Set DS345 Menu
7-5
Trigger Menu
7-6
Zoom Menu
7-6
Other Menu
7-7
Mouseless Operation
7-7
File Format
7-7
DS345 Circuitry
Circuit Description
8-1
Bottom PC Board
8-1
Power Supplies
8-1
Microprocessor System
8-1
Display and Keyboard
8-1
Ribbon Cable, Trigger and Sync
8-2
GPIB and RS232 Interfaces
8-2
Output Amplifier
8-3
Output Attenuator
8-3
Top PC Board
8-4
Ribbon Cable, ADC, DACs
8-4
Clocks
8-4
DDS ASIC and Memory
8-5
Amplitude and Sweep DACs
8-5
DDS Waveform DAC
8-6
DDS Output Filters and Doubler
8-6
Sync and Gain Adjust
8-6
Component Parts List
9-1
Bottom PC Board and Front Panel
9-1
Top PC Board
9-10
Optional PC Board
9-20
Miscellaneous Parts
9-22
ii
iii
Schematic Circuit Diagrams Sheet No.
Bottom PC Board
Power Supplies
1/7
Microprocessor System
2/7
Display and Keyboard
3/7
Ribbon Cable, Trigger and Sync
4/7
GPIB and RS232 Interfaces
5/7
Output Amplifier
6/7
Output Attenuator
7/7
Top PC Board
Ribbon Cable, ADC, DACs
1/7
Clocks
2/7
DDS ASIC and Memory
3/7
Amplitude and Sweep DACs
4/7
DDS Waveform DAC
5/7
DDS Output Filters and Doubler
6/7
Sync and Gain Adjust
7/7
Front Panel
Keypad
1/2
LED Display
2/2
Bottom PCB Component Placement
Top PCB Component Placement
DS345 SYNTHESIZED FUNCTION GENERATOR
DS345 SYNTHESIZED FUNCTION GENERATOR
vi
Symbols you may find on SRS products
Symbol
Description
Alternating current
Caution - risk of electrical shock
Frame or chassis terminal
Caution - refer to accompanying documents
Earth (ground) terminal
Battery
Fuse
On (supply)
Off (supply)
DS345 SYNTHESIZED FUNCTION GENERATOR
Safety and Preparation for Use
This instrument may be damaged if operated
with the LINE VOLTAGE SELECTOR set for the
wrong ac line voltage or if the wrong fuse is installed.
LINE VOLTAGE SELECTION
The DS345 operates from a 100V, 120V, 220V, or
240V nominal ac power source having a line frequency of 50 or 60 Hz. Before connecting the power cord to a power source, verify that the LINE
VOLTAGE SELECTOR card, located in the rear
panel fuse holder, is set so that the correct ac input
voltage value is visible.
Conversion to other ac input voltages requires a
change in the fuse holder voltage card position and
fuse value. Disconnect the power cord, open the
fuse holder cover door and rotate the fuse-pull lever
to remove the fuse. Remove the small printed circuit board and select the operating voltage by
orienting the board so that the desired voltage is
visible when it is pushed firmly back into its slot.
Rotate the fuse-pull lever back into its normal position and insert the correct fuse into the fuse holder.
LINE FUSE
Verify that the correct line fuse is installed before
connecting the line cord. For 100V/120V, use a
1 Amp fuse and for 220V/240V, use a 1/2 Amp
fuse.
LINE CORD
The DS345 has a detachable, three-wire power
cord for connection to the power source and to a
protective ground. The exposed metal parts of the
instrument are connected to the outlet ground to
protect against electrical shock. Always use an
outlet which has a properly connected protective
ground.
WARNING:
Dangerous voltages, capable of causing death, are present in this instru-
ment. Use extreme caution whenever the instrument covers are removed.
v
DS345 SYNTHESIZED FUNCTION GENERATOR
vi
FREQUENCY RANGE
Waveform
Maximum Freq
Resolution
Sine
30.2 MHz
1 µHz
Square
30.2 MHz
1 µHz
Ramp
100 KHz
1 µHz
Triangle
100 KHz
1 µHz
Noise
10 MHz
(Gaussian Weighting)
Arbitrary
10 MHz
40 MHz sample rate
OUTPUT
Source Impedance
50
Ω
Output may float up to ±40V (AC + DC) relative to earth ground.
AMPLITUDE
Range
into 50Ω load (limited such that
|V
ac peak
| + |Vdc| ≤ 5 V)
vii
SPECIFICATIONS
V
pp
V
rms
dBm (50Ω)
Function
Max.
Min.
Max.
Min.
Max.
Min.
Sine
10V
10 mV
3.54V
3.54 mV
+23.98
-36.02
Square
10V
10 mV
5V
5 mV
+26.99
-33.0
Triangle
10V
10 mV
2.89V
2.89 mV
+22.22
-37.78
Ramp
10V
10 mV
2.89V
2.89 mV
+22.22
-37.78
Noise
10V
10 mV
2.09V
2.09 mV
+19.41
-40.59
Arbitrary
10V
10 mV
n.a.
n.a.
n.a.
n.a.
Resolution
3 digits (DC offset = 0V)
Accuracy (with 0V DC Offset)
Sine:
1µHz
100 kHz
20 MHz
30.2 MHz
10Vpp
±0.2 dB
±0.2dB
±0.3dB
5Vpp
±0.4dB
±0.4dB
±0.5dB
0.01Vpp
Square:
1µHz
100 kHz
20 MHz
30.2 MHz
10Vpp
±3 %
±6%
±15%
5Vpp
±5%
±8%
±18%
0.01Vpp
Triangle, Ramp, Arbitrary:
±3% > 5Vpp
±5% < 5Vpp
Specifications
DC OFFSET
Range:
±5V (limited such that
|V
ac peak
| + |Vdc| ≤ 5 V)
Resolution:
3 digits (VAC = 0)
Accuracy:
1.5% of setting + 0.2 mV (DC only)
±0.8 mV to ±80 mV depending on AC and DC settings
WAVEFORMS
Sinewave Spectral Purity
Spurious:
< -50 dBc (non-harmonic)
Phase Noise:
< -55 dBc in a 30 KHz band centered on the carrier, exclusive of
discrete spurious signals
Subharmonic:
< -50 dBc
Harmonic Distortion: Harmonically related signals will be less than:
Level
Frequency Range
< -55 dBc
DC to 100 KHz
< -45 dBc
.1 to 1 MHz
< -35 dBc
1 to 10 MHz
< -25 dBc
10 to 30 MHz
Square Wave
Rise/Fall Time:
< 15 nS (10 to 90%), at full output
Asymmetry:
< 1% of period + 4nS
Overshoot:
< 5% of peak to peak amplitude at full output
Ramps, Triangle and Arbitrary
Rise/Fall Time
35 nS (10 MHz Bessel Filter)
Linearity
±0.5% of full scale output
Settling Time
< 1 µs to settle within 0.1% of final value at full output
Arbitrary Function
Sample Rate:
40 MHz/N, N = 1 to 234-1.
Memory Length:
8 to 16,300 points
Resolution:
12 bits (0.025% of full scale)
PHASE
Range:
±7199.999° with respect to arbitrary starting phase
Resolution:
0.001°
AMPLITUDE MODULATION
Source:
Internal (sine, square, triangle, or ramp) or External
Depth:
0 to 100% AM or DSBSC
Rate:
0.001 Hz to 10 kHz internal, 20 kHz max external
Distortion:
< -35dB at 1kHz, 80% depth
viii
Specifications
DSB Carrier:
< -35db typical at 1 kHz modulation rate (DSBSC)
Ext Input:
±5V for 100% modulation, 100 kΩ impedance.
FREQUENCY MODULATION
Source:
Internal (sine, square, triangle, ramp)
Rate:
0.001 Hz to 10 kHz
Span:
1 µHz to 30.2 MHz (100 kHz for triangle or ramp)
PHASE MODULATION
Source:
Internal (sine, square, triangle, ramp)
Rate:
0.001 Hz to 10 kHz
Span:
±7199.999°
FREQUENCY SWEEP
Type:
Linear or Log, phase continuous
Waveform:
up, down, up-down, single sweep
Time:
0.001s to 1000s
Span:
1 µHz to 30.2 MHz (100 kHz for triangle,ramp)
Markers:
Two markers may be set at any sweep point (TTL output)
Sweep Output:
0 - 10 V linear ramp signal, syncronized to sweep
BURST MODULATION
Waveform:
any waveform except NOISE may be BURST
Frequency:
Sine, square to 1 MHz; triangle, ramp to 100 kHz; arbitrary to 40
MHz sample rate
Count:
1 to 30,000 cycles/burst (1µs to 500s burst time limits)
TRIGGER GENERATOR
Source:
Single, Internal, External, Line
Rate:
0.001 Hz to 10 kHz internal (2 digit resolution)
External:
Positive or Negative edge, TTL input
Output:
TTL output
TIMEBASE
Accuracy
±5 ppm (20 to 30° C)
Aging
5 ppm/year
Input
10 MHz/N ± 2 ppm. N = 1 to 8. 1V pk-pk minimum input level.
Output
10 MHz, >1 Vpp sine into 50 Ω
Optional Timebase
Type:
Ovenized AT-cut oscillator
Stability:
< 0.01ppm, 20 - 60°C
Aging:
< 0.001ppm/day
Short Term:
< 5 x 10
-11
1s Allan Variance
ix
Specifications
GENERAL
Interfaces
RS232-C (300 to 19200 Baud, DCE) and IEEE-488.2 with free
DOS Based Arbitrary Waveform Software
All instrument functions are controllable over the interfaces.
Weight
10 lbs
Dimensions
8.5" x 3.5" x 13" (W x H x L)
Power
50 VA, 100/120/220/240 Vac 50/60 Hz
x
Abridged Command List
Syntax
Variables i,j are integers. Variable x is a real number in integer, real, or exponential notation.
Commands which may be queried have a ? in parentheses (?) after the mnemonic. The ( ) are not sent.
Commands that may
only
be queried have a '?' after the mnemonic. Commands which
may not
be quer-
ied have no '?'. Optional parameters are enclosed by {}.
Function Output Control Commands
AECL
Sets the output amplitude/offset to ECL levels (1Vpp, -1.3V offset).
AMPL(?) x
Sets the output amplitude to x. x is a value plus units indicator. The units can be
VP (Vpp), VR (Vrms), or DB (dBm). Example: AMPL 1.00VR sets 1.00 Vrms.
ATTL
Sets the output amplitude/offset to TTL levels (5 Vpp, 2.5 V offset).
FREQ(?) x
Sets the output frequency to x Hz.
FSMP(?) x
Sets the arbitrary waveform sampling frequency to x Hz.
FUNC(?) i
Sets the output function. 0 = sine, 1 = square, 2 = triangle, 3 = ramp, 4 = noise,
5= arbitrary.
INVT(?)i
Set output inversion on (i=1) or off (i=0).
OFFS(?)x
Sets the output offset to x volts.
PCLR
Sets the current waveform phase to zero.
PHSE(?) x
Sets the waveform output phase to x degrees.
Modulation control commands
*TRG
Triggers bursts/single sweeps if in single trigger mode.
BCNT(?) i
Sets the burst count to i.
DPTH(?) i
Sets the AM modulation depth to i %. If i is negative sets DSBSC with i % modulation.
FDEV(?) x
Sets the FM span to x Hz.
MDWF(?) i
Sets the modulation waveform. 0 = single sweep, 1 = ramp, 2 = triangle, 3 = sine,
4 = square, 5 = arbitrary, 6 = none.
MENA(?) i
Turns modulation on (i=1) or off (i=0).
MKSP
Sets the sweep markers to the extremes to the sweep span.
MRKF(?) i ,x
Sets marker frequency i to x Hz. 0 = mrk start freq, 1 = stop freq, 2 = center
freq, 3 = span.
MTYP(?) i
Sets the modulation type. 0 = lin sweep, 1 = log sweep, 2 = AM, 3 = FM, 4 = PM,
5 = Burst.
PDEV(?) x
Sets the phase modulation span to x degrees.
RATE(?) x
Sets the modulation rate to x Hz.
SPAN(?) x
Sets the sweep span to x Hz.
SPCF(?) x
Sets the sweep center frequency to x Hz.
SPFR(?) x
Sets the sweep stop frequency to x Hz.
SPMK
Sets the sweep span to the sweep marker positions.
STFR(?) x
Sets the sweep start frequency to x Hz.
TRAT(?) x
Sets the internal trigger rate to x Hz.
TSRC(?) i
Sets the trigger source. 0 = single, 1 = internal, 2 = + Ext, 3 = - Ext, 4 = line.
Arbitrary Waveform and Modulation commands
AMRT(?) i
Sets the arbitrary modulation rate divider to i.
AMOD? i
Allows downloading a i point arbitrary modulation waveform if the modulation
type is AM, FM, or PM. After execution of this query the DS345 will return the
ASCII value 1. The binary waveform data may now be downloaded.
xi
Abridged Command List
LDWF? i,j
Allows downloading a j point arbitrary waveform of format i. i = 0 = point format, i= 1
= vector format. After execution of this query the DS345 will return the ascii value 1.
The binary waveform data may now be downloaded.
Setup Control Commands
*IDN?
Returns the device identification .
*RCL i
Recalls stored setting i.
*RST
Clears instrument to default settings.
*SAV i
Stores the current settings in storage location i.
Status Reporting Commands
*CLS
Clears all status registers.
*ESE(?)
j
Sets/reads the standard status byte enable register.
*ESR?
{j}
Reads the standard status register, or just bit j of register.
*PSC(?)
j
Sets the power on status clear bit. This allows SRQ's on power up if desired.
*SRE(?)
j
Sets/reads the serial poll enable register.
*STB?
{j}
Reads the serial poll register, or just bit n of register.
STAT?
{j}
Reads the DDS status register, or just bit n of register.
DENA(?)
j
Sets/reads the DDS status enable register.
Hardware Test and Calibration Control
*CAL?
Starts autocal and returns status when done.
*TST?
Starts self-test and returns status when done.
xii
Status Byte Definitions
Serial Poll Status Byte
bit
name
usage
0
Sweep Done
set when no sweeps in progress
1
Mod Enable
set when modulation is enabled
2
User SRQ
set when the user issues a front
panel SRQ
3
DDS
set when an unmasked bit in DDS
status byte is set
4
MAV
set when GPIB output queue is
non-empty
5
ESB
set when an unmasked bit in std
event status byte is set
6
RQS
SRQ bit
7
No Command
set when there are no unexecuted
commands in input queue
Standard Event Status Byte
bit
name
usage
0
unused
1
unused
2
Query Error
set on output queue overflow
3
unused
4
Execution Err
set on error in command execution
5
Command Err
set on command syntax error
6
URQ
set on any front panel key
press
7
PON
set on power on
DDS Status Byte
bit
name
usage
0
Trig'd
set on burst/sweep trigger
1
Trig Error
set on trigger error
2
Ext Clock
set when locked to an external
clock
3
Clk Error
set when an external clock er-
ror occurs
4
Warmup
set when the DS345 is warmed
up
5
Test Error
set when self test fails
6
Cal Error
set when autocal fails
7
mem err
set on power up memory error
Getting Started
Introduction
This section is designed to familiarize you with the operation of the DS345
Synthesized Function Generator. The DS345 is a powerful, flexible generator
capable of producing both continuous and modulated waveforms of exceptional purity and resolution. The DS345 is also relatively simple to use, the
following examples take the user step by step through some typical uses.
Data Entry
Setting the DS345's operating parameters is done by first pressing the key
with the desired parameter's name on it (FREQ, for example, to set the frequency). Some parameters are labelled above the keys in light gray. To display these values first press the SHIFT key and then the labelled key.
[SHIFT][SWP CF] for example, displays the sweep center frequency. Values
are changed through the numeric keypad or the MODIFY keys. To enter a
value simply type the new value using the keypad and complete the entry by
hitting one of the UNITS keys. If the entry does not have units, any of the
UNITS keys may be pressed. If an error is made, pressing the CLR key returns the previous value. The current parameter value may also be increased
or decreased with the MODIFY keys. Pressing the UP ARROW key will increase the value by the current step size, while pressing the DOWN ARROW
key will decrease the value by the current step size. If the entered value is
outside of the allowable limits for the parameter the DS345 will beep and display an error message.
Step Size
Each parameter has an associated step size which may be an exact power
of 10 (1 Hz, 10 Hz or 100 Hz for example), or may be an arbitrary value. If
the step size is an exact power of 10, that digit of the display will flash. Pressing [STEP SIZE] displays the step size for the current parameter (the STEP
LED will be lit). Pressing [STEP SIZE] again returns the display to the previously displayed parameter. The step size may be changed by typing a new
value while the STEP LED is lit. Pressing the MODIFY UP ARROW key while
the step size is displayed increases the step size to the next larger decade,
while pressing the MODIFY DOWN ARROW key will decrease the step size
to the next smaller decade.
CW Function Generation
Our first example demonstrates generating CW waveforms and the DS345's
data entry functions. Connect the front panel FUNCTION output to an oscilloscope, terminating the output into 50 ohms. Turn the DS345 on and wait until
the message "TEST PASS" is displayed.
1
1)
Press [SHIFT][DEFAULTS].
2)
Press [AMPL]. Then press [5][Vpp].
3)
Press [FUNCTION DOWN ARROW] twice.
4)
Press [FREQ] and then [1][0][kHz].
This recalls the DS345's default settings.
Displays the amplitude and sets it to 5 Vpp. The
scope should show a 5 Vpp 1 kHz sine wave.
The function should change to a square wave and
then a triangle wave.
Displays the frequency and sets it to 10 kHz. The
scope should now display a 10 kHz triangle wave.
1-1
Getting Started
5) Press [MODIFY UP ARROW].
6) Press [STEP SIZE].
7) Press [1][2][3][Hz]. Then press [STEP SIZE].
8) Press [MODIFY DOWN ARROW].
9) Press [STEP SIZE] then [MODIFY UP ARROW]
10) Press [STEP SIZE].
11) Press [MODIFY UP ARROW].
The frequency will increment to 10.1 kHz. The
flashing digit indicates a step size of 100 Hz.
Observe that the step size is indeed 100 Hz. The
STEP LED should be on.
We've changed the step size to 123 Hz and displayed the output frequency again.
The frequency is decreased by 123 Hz to
9977 Hz.
The step size is displayed and is increased from
123 Hz to the next larger decade–1 kHz.
The frequency is displayed again. The flashing
digit indicates that the step size is 1 kHz.
The frequency is incremented to 10.977 kHz.
Frequency Sweep
The next example sets up a linear frequency sweep with markers. The
DS345 can sweep the output frequency of any function over any range of allowable output frequencies. There are no restrictions on minimum or maximum sweep span. The sweep time may range from 1 ms to 1000 s. The
DS345 also has two independent rear-panel markers that may be used indicate specific frequencies in the sweep. The MARKER output goes high at the
start marker position and low at the stop marker position.
An oscilloscope that can display three channels is required. Attach the
FUNCTION output BNC to the oscilloscope, terminating the output into 50
ohms. Set the scope to 2V/div. Attach the SWEEP rear-panel BNC to the
scope and set it to 2V/div. The scope should be set to trigger on the falling
edge of this signal. Attach the MARKER rear-panel BNC to the scope's third
channel. This signal will have TTL levels.
1) Press [SHIFT][DEFAULTS].
2) Press [AMPL] then [5][Vpp].
3) Press [SWEEP MODE UP ARROW] twice.
4) Press [RATE] then [1][0][0][Hz].
5) Press [START FREQ] then [1][0][0][kHz].
This recalls the DS345's default settings.
Set the amplitude to 5Vpp.
Set the modulation type to linear sweep.
Set the sweep rate to 100 Hz. The sweep will take
10 ms (1/100Hz). Set the scope time base to
1ms/div.
Set the sweep start frequency to 100 kHz.
1-2
Getting Started
6) Press [SHIFT][STOP F] then [1][MHz].
7) Press [SWEEP ON/OFF].
8) Press [SHIFT][MRK STOP] then [9][0][0][kHz].
9) Press [SHIFT][MRK START] then [2][0][0][kHz].
10) Press [SHIFT][SPAN=MRK].
Set the stop frequency to 1 MHz.
This starts the sweep. The MOD/SWP LED will
light, indicating that the DS345 is sweeping. The
scope should show the SWEEP output as a 0V to
10 V sawtooth wave. The sweep starts at 100kHz
when the sawtooth is at 0 V and moves to 1MHz
when the sawtooth is at 10 V. The FUNCTION
output is the swept sine wave. The markers are
not yet active.
Display the stop marker position and set the stop
marker to 900 kHz. The marker should now be
high from the start of the sweep to 900kHz (9V on
the sweep sawtooth), then the marker should go
low.
Set the start marker to 200 kHz. The marker is
now low from the beginning of the sweep until the
200 kHz start marker (2V on the sawtooth). The
marker stays high until the 900 kHz stop marker.
The markers allows designating any two frequencies in the sweep.
This sets the sweep span to the marker positions.
The sweep now goes from 200 kHz to 900 kHz.
This function allows zooming in on any feature in
the sweep without entering the frequencies.
Tone Bursts
This example demonstrates the DS345's tone burst capability. The DS345
can produce a burst of 1 to 30,000 cycles of any of its output functions. The
bursts may be triggered by the internal rate generator, the line frequency, a
front panel button, or an external rising or falling edge. The TRIGGER output
goes high when the burst is triggered and low when the burst is over.
Connect the DS345's FUNCTION output to an oscilloscope, terminating the
output into 50 ohms. Set the sensitivity to 2V/div. Connect the rear-panel
TRIGGER output to the scope and set 2V/div. Trigger the scope on the rising
edge of the TRIGGER output. Set the scope timebase to 0.5ms/div.
1) Press [SHIFT][DEFAULTS].
2) Press [AMPL] then [5][Vpp].
3) Press [FREQ] then [1][0][kHz].
This recalls the DS345's default settings.
Set the amplitude to 5Vpp.
Set the output frequency to 10 kHz. This will be
the frequency of the tone.
1-3
Getting Started
4) Press [SWEEP MODE DOWN ARROW] three
times.
5) Press [SHIFT][BRST CNT]. Then [1][0][Hz].
6) Press [SHIFT][TRIG SOURCE] Then press
[MODIFY UP ARROW].
7) Press [SHIFT][TRIG RATE] then [4][0][0][Hz].
8) Press [SWEEP ON/OFF].
9) Press [SHIFT][BRST CNT].
10) Press [MODIFY DOWN ARROW] twice.
Set the modulation type to BURST.
Set the number of pulses in the burst to 10. Any
of the units keys may be used to terminate the entry.
Display the burst trigger source. Then change the
source from single trigger to the internal trigger
rate generator.
Set the internal trigger rate generator to 400 Hz.
Enable the burst. The MOD/SWP LED will light.
The scope should show two bursts of 10 cycles of
a sine wave.
Display the burst count again.
There should now be 8 pulses in each burst.
1-4
Introduction to Direct Digital Synthesis
Accumulator
48 bits
External Control
DAC
Frequency
Filter
Direct Digital Synthesis
+
Introduction
Traditional Generators Frequency synthesized function generators typically use a phase-locked loop
Arbitrary Waveforms Arbitrary function generators bypass the need for wave-shaping circuitry.
Direct Digital Synthesis (DDS) is a method of generating very pure waveforms with extraordinary frequency resolution, low frequency switching time,
crystal clock-like phase noise, and flexible modulation. As an introduction to
DDS let's review how traditional function generators work.
(PLL) to lock an oscillator to a stable reference. Wave-shaping circuits are
used to produce the desired function. It is difficult to make a very high resolution PLL so the frequency resolution is usually limited to about 1:106 (some
sophisticated fractional-N PLLs do have much higher resolution). Due to the
action of the PLL loop filter, these synthesizers typically have poor phase jitter and frequency switching response. In addition, a separate wave-shaping
circuit is needed for each type of waveform desired, and these often produce
large amounts of waveform distortion.
Usually, a PLL is used to create a variable frequency clock that increments
an address counter. The counter addresses memory locations in waveform
RAM, and the RAM output is converted by a high speed digital-to-analog
converter (DAC) to produce an analog waveform. The waveform RAM can be
filled with any pattern to produce "arbitrary" functions as well as the usual
sine, triangle, etc. The sampling theorem states that, as long as the sampling
rate is greater than twice the frequency of the waveform being produced, with
an appropriate filter the desired waveform can be perfectly reproduced. Since
the frequency of the waveform is adjusted by changing the clock rate, the
output filter frequency must also be variable. Arbitrary generators with a PLL
suffer the same phase jitter, transient response, and resolution problems as
synthesizers.
DDS DDS also works by generating addresses to a waveform RAM to produce
data for a DAC. However, unlike earlier techniques, the clock is a fixed frequency reference. Instead of using a counter to generate addresses, an adder is used. On each clock cycle, the contents of a Phase Increment Register
are added to the contents of the Phase Accumulator. The Phase Accumulator output is the address to the waveform RAM (see diagram below). By
changing the Phase Increment the number of clock cycles needed to step
DDS ASIC
Figure 1: Block diagram
of SRS DDS ASIC
Fixed
Frequency
Reference
Phase
Increment
Register
48 Bits
Modulation CPU
Phase
Modulation RAM
Waveform
RAM
16k points
Fixed
2-1
Introduction
through the entire waveform RAM changes, thus changing the output frequency.
Frequency changes now can be accomplished phase continuously in only
one clock cycle. And the fixed clock eliminates phase jitter and requires only
a simple fixed frequency anti-aliasing filter at the output.
The DS345 uses a custom Application Specific Integrated Circuit (ASIC) to
implement the address generation in a single component. The frequency resolution is equal to the resolution with which the Phase Increment can be set.
In the DS345, the phase registers are 48 bits long, resulting in an impressive
1:1014 frequency resolution. The ASIC also contains a modulation control
CPU that operates on the Phase Accumulator, Phase Increment, and external circuitry to allow digital synthesis and control of waveform modulation.
The Modulation CPU uses data stored in the Modulation RAM to produce
amplitude, frequency, phase, and burst modulation, as well as frequency
sweeps. All modulation parameters, such as rate, frequency deviation, and
modulation index, are digitally programmed.
DDS gives the DS345 greater flexibility and power than conventional synthesizers or arbitrary waveform generators without the drawbacks inherent in
PLL designs.
DS345 Description
12 bit
DAC
10 MHz Bessel Filter
x2
Output
Amp
Attenuators
Function
Output
Square Wave
Comparator
Sync
Output
AM Input
Modulation RAM
40MHz Clock
DDS345 ASIC
Amplitude DAC
Waveform
RAM
Amplitude
Control
Cauer Filter
Figure 2: DS345 Block Diagram
A block diagram of the DS345 is shown in Figure 2. The heart of the DS345
is a 40 MHz crystal clock. This clock is internally provided, but may be phase
locked to an external reference. The 40 MHz clock controls the DDS345
ASIC, waveform RAM, and high-speed 12bit DAC. Sampling theory limits
the frequency of the waveform output from the DAC to about 40% of 40 MHz,
or 15 MHz. The 48 bit length of the DDS345's PIR's sets the frequency resolution to about 146 nHz. These parameters and the DAC's 12 bit resolution
define the performance limits of the DS345.
2-2
Introduction
The reconstruction filter is key to accurately reproducing a waveform in a
sampled data system. The DS345 contains two separate filters. For sine
w
ave generation the output of the DAC goes through a 9th order Cauer filter,
while ramps, triangles, and arbitrary waveforms pass instead through a
10
MHz 7
th
order Bessel filter. The Cauer filter has a cutoff frequency of 16.5
MHz and a stopband attenuation of 85dB, and also includes a peaking circuit
to correct for the sine(x)/x amplitude response characteristic of a sampled
system. This filter eliminates any alias frequencies from the waveform output
and allows generation of extremely pure sine waves. The output of the Cauer
filter is then frequency doubled by an analog multiplier. This multiplies the
DAC's 0 - 15 MHz output frequency range to the final 0 - 30 MHz range. However, the Cauer filter has very poor time response and is only useful for CW
waveforms. Therefore, the Bessel filter was chosen for its ideal time response, eliminating rings and overshoots from stepped waveform outputs.
This filter limits the frequency of arbitrary waveforms to 10 MHz and rise
times to 35 ns.
The output of the filters pass to an analog multiplier that controls the amplitude of the waveform. This multiplier controls the waveform amplitude with an
AM signal that may come from either the ASIC or the external AM input. This
allows both internally and externally controlled amplitude modulation. The
amplitude control is followed with a wide bandwidth power amplifier that outputs 10 V peak-to-peak into a 50 ohm load with a rise time of less than 15 ns.
The output of the power amplifier passes through a series of three step attenuators (6, 12, and 24 dB) that set the DS345's final output amplitude. The
post amplifier attenuators allow internal signal levels to remain as large as
possible, minimizing output noise and signal degradation.
Square waves and waveform sync signals are generated by discriminating
the function waveform with a high-speed comparator. The output of the comparator passes to the SYNC OUTPUT and, in the case of square waves, to
the amplitude control multiplier input. Generating square waves by discriminating the sine wave signal produces a square wave output with rise and fall
times much faster than allowed by either of the signal filters.
2-3
Introduction
2-4
OUTPUTS
FUNCTION
SYNC
REM SRQ
ACT ERR
EXT ERR
ARB
NOISE
BURST
Φ
FM
AM (INT)
LOG SWP
LIN SWP
m
TRIG'D SINGLE
ARB
MOD/SWP SHIFT
Hz dBm
DEG Vrms
% Vpp
FREQ AMPL OFFS PHASE TRIG STEP SPAN RATE MRK STRT f STOP f
ON/STBY
SRS
STANFORD RESEARCH SYSTEMS MODEL DS345 30MHz SYNTHESIZED FUNCTION GENERATOR
TIMEBASE
STATUS
50
Ω
40V max.
TTL
ECL
TTL
REL=0
TRIG SWP CF
BRST CNT
STOP f
MRK START
GPIB
TRIG SOURCE
MRK STOP
SRQ
TRIG RATE
ARB EDIT
MRK CF
RS232
MRK=SPAN
DEFAULTS
MRK SPAN
DATA
SPAN=MRK
CALIBRATE
LOCAL
AMPL
FREQ
OFFST
PHASE
RATE
SWEEP
ON/OFF
SPAN
(DEPTH)
START
FREQ
SHIFT STO RCL CLR
DEG
%
MHz
dBm
kHz
Vrms
Hz
Vpp
STEP
SIZE
0
.
+/-
1
4
7
2
5
8
3
6
9
FUNCTION
MODULATION
FUNCTION SWEEP/MODULATE MODIFYENTRY
1
2
3
4
6
7
8
9
10
11
12
5
1) Power Switch
The power switch turns the DS345 on and off. In the STBY position power is
maintained to the DS345's internal oscillator, minimizing warmup time.
2) MODIFY Keys
The modify keys permit the operator to increase or decrease the displayed
parameter value. The step size may be determined by pressing the STEP
SIZE key (the STEP LED will light). Every displayed parameter has an associated step size, pressing the MODIFY UP arrow key adds the step size to
the current value, while pressing the MODIFY DOWN arrow key subtracts
the step size from the current value. If the step size is set to an exact power
of 10 (1, 10, or 100, for example) the corresponding digit of the display will
flash. To change the step size, display the step size and then either enter a
new value with the ENTRY keys or the MODIFY keys. Pressing the MODIFY
UP arrow while the step LED is lit will increase the step size to the next larger
decade, while pressing the MODIFY DOWN arrow will decrease the step size
to the next smaller decade. The MODIFY UP/DOWN arrows also select between different menu selections (ie., trigger source). Sometimes the parameter display will have more than one parameter displayed at a time, and the
[SHIFT][LEFT] and [SHIFT][RIGHT] keys will select between these values.
3) ENTRY Keys
The numeric keypad allows for direct entry of the DS345's parameters. To
change a parameter value simply type the new value using the keypad. The
value is entered by terminating the entry with one of the UNITS keys. A typing error may be corrected by using the CLR key. The +/- key may be selected at any time during number entry.
4) Units Keys
The UNITS keys are used to terminate numeric entries. Simply press the key
with the desired units to enter the typed value. Some parameters don't have
2-5
Front Panel Features
DS345 FEATURES
any associated units and
any
of the units keys may be used to enter the value. When the amplitude is displayed, pressing a units key without entering a new value will displayed the amplitude in the new units. This
allows the am
plitude display to be switched between Vpp, Vrms, and dBm without entering
a new value.
5) Shift Key
The shift key is used to select the functions printed in gray above the keys.
Press [SHIFT] and then [key] to select the desired function (for example
[SHIFT][SWP CF] to display the sweep center frequency). When the SHIFT
key is pressed the SHIFT LED will light. This indicates that the keyboard is in
shift mode. Pressing [SHIFT] a second time will deactivate shift mode.
6) Modulation Keys
These keys control the DS345's modulation capabilities. The MODULATION
TYPE up/down arrow keys select the modulation type. The MODULATION
WAVEFORM up/down arrow keys select the waveform of the modulating
function. The [SWEEP ON/OFF] key turns the modulation on and off. When
the modulation is turned on the MOD/SWP LED will light. If the modulation
parameters are not permitted for the selected output function, an error message will be displayed and modulation will not be turned on. Some modulation parameters are not relevant to all modulation types (start frequency is
not relevant to AM, for example), and the message "NOT APPLIC" will be
displayed if they are selected.
7) Function Keys
These keys choose the main function output. The FUNCTION up/down arrow
keys select between the output functions. If the output frequency is set beyond of the range allowed for a waveform (> 100 kHz for triangle and ramp) a
message will be displayed and the frequency will be set to the maximum allowed for that function.
8) Main Function BNC
This output has an impedance of 50Ω. If it is terminated into an impedance
other than 50Ω the output amplitude will be incorrect and may exhibit increased distortion. The shield of this output may be floated up to ±40V relative to earth ground.
9) Sync Output BNC
This output is a TTL square wave synchronized to the main function output
and has a 50Ω output impedance. The shield of this output may be floated up
to ±40V relative to earth ground.
10) Status LEDs
These six LEDs indicate the DS345's status. The LED functions are:
name
function
REM
The DS345 is in GPIB remote state. The STEP SIZE key returns local control.
SRQ
The DS345 has requested service on the GPIB interface.
ACT
Flashes on RS232/GPIB activity.
ERR
Flashes on an error in the execution of a remote command.
EXT CLOCK
The DS345 has detected a signal at its TIMEBASE input and
is trying to phase lock to it.
CLOCK ERR
The DS345 is unable to lock to the signal at the TIMEBASE
input. This is usually because the signal is too far (>2ppm)
from the nominal values of 10, 5, 3.33, 2.5 or 1.25 MHz.
11) Parameter Display
This 12 digit display shows the value of the currently displayed parameter.
The LEDs below the display indicate which parameter is being viewed. Error
messages may also appear on the display. When an error message is displayed you can return to the normal operation by pressing any key.
2-6
12) Units LEDs
These LEDs indicate the units of the displayed value. If no LED is lit the number displayed has no units.
Rear Panel Features
FUSE: 3/4A (100/120VAC) or 3/8A (220/240VAC)
TRIGGER AM(EXT) TIMEBASE
TRIGGER MODULATION 10MHz
SWEEP MARKER BLANK/LIFT
TTL 0-5V 10MHz
TTL 0-5V 1V
TTLTTL0-10V
INPUTS
OUTPUTS
WARNING: No user serviceable parts inside.
Refer to operation manual for safety notice.
For use by qualified laboratory personnel only.
!
IEEE-488 STD PORT (GPIB) RS232 (DCE, 8d, 0p, 2s bits)
1
2
3
4
5
1) Power Entry Module
This contains the DS345's fuse and line voltage selector. Use a 3/4 amp fuse
for 100/120 volt operation, and a 3/8 amp fuse for 220/240 volt operation. To
set the line voltage selector for the correct line voltage first remove the fuse.
Then, remove the line voltage selector card and rotate the card so that the
correct line voltage is displayed when the card is reinserted. Replace the
fuse.
2) External Inputs
Trigger Input
The trigger input is a TTL compatible input used to trigger modulation sweeps
and bursts. This input has a 10 kΩ input impedance. The shield of this input is
tied to that of the function output and may be floated up to ±40V relative to
earth ground.
AM Input
The AM input controls the amplitude of the function output. This input has a
100 kΩ input impedance and a ±5V range, where +5V sets the output to
100% of the front panel setting, 0V sets the output to 0, and -5V sets the output to -100% of the setting. The 0 to 5V range is used for normal AM operation, while the ±5V range is used for DSBSC modulation. This input is always
active and should
only
be be connected if AM is desired. The shield of this input is tied to the shield of the function output and may be floated up to ±40V
relative to earth ground.
DS345 FEATURES
2-7
DS345 FEATURES
Timebase Input
This 1kΩ impedance input allows the DS345 to lock to an external timebase.
The external source should be greater than 1V pk-to-pk and should be within
±2 ppm of 10 MHz or any subharmonic down to 1.25 MHz.
The shield of
this input is connected to earth ground.
3) Auxiliary Outputs
10 MHz Output
This output produces a >1V pk-pk 10 MHz sinewave from the DS345's internal oscillator. It expects a 50Ω termination.
The shield of this output is
connected to earth ground.
Modulation Out
This output generates a 0 - 5V representation of the current modulation function. The shield of this output is tied to that of the function output and may be
floated up to ±40V relative to earth ground.
Trigger Output
This TTL compatible output goes high when a triggered sweep or burst begins, and goes low when it ends. This may be used to synchronize an external device to the sweep/burst. The shield of this output is tied to that of the
function output and may be floated up to ±40V relative to earth ground.
Sweep Output
This output generates a 0 - 10 V ramp that is synchronous with the DS345's
frequency sweep. The shield of this output is tied to that of the function output and may be floated up to ±40V relative to earth ground.
Marker Output
This TTL compatible output goes high when the DS345's frequency sweep
passes the start marker frequency, and goes low when the sweep passes the
stop marker frequency. The shield of this output is tied to that of the function
output and may be floated up to ±40V relative to earth ground.
Blank/Lift Out
This TTL compatible output is low during the upsweep of a frequency sweep,
and is high during the sweep retrace. The shield of this output is tied to that
of the function output and may be floated up to ±40V relative to earth ground.
4) GPIB Connector
If the DS345 has the optional GPIB/RS232 interface this connector is used
for IEEE-488.1 and .2 compatible communications.
The shield of this con-
nector is connected to earth ground.
5) RS232 Connector
If the DS345 has the optional GPIB/RS232 interface this connector is used
for RS232 communication. The DS345 is a DCE and accepts 8 bits, no parity, 2 stop bits and 300 and 19.2k Baud.
The shield of this connector is
connected to earth ground.
2-8
DS345 OPERATION
SYNC
FUNCTION
40V max
50
Ω
TTL
NOISE
TRIG'D
FREQ
AMPL
TTL
ECL
OFFST
REL=O
PHASE
ARB
Introduction The following sections describe the operation of the DS345. The first section
describes the basics of setting the function, frequency, amplitude, and offset.
The second section explains sweeps and modulation. The third section explains storing and recalling setups, running self-test and autocalibration, and
setting the computer interfaces. The fourth and last section describes front
panel editing of arbitrary waveforms.
Power-On When the power is first applied to the DS345 the unit will display its serial
number and ROM version for about three seconds. The DS345 will then initiate a series of self-tests of the circuitry and stored data. The test should
take about three seconds and end with the message "TEST PASS". If the
self test fails the DS345 will display an error message indicating the nature of
the problem (see the TROUBLESHOOTING section for more details, page 4-
1). The DS345 will attempt to operate normally after a self-test failure, (pressing any key will erase the error message).
SETTING THE FUNCTION
OUTPUTS The FUNCTION and SYNC BNCs are the DS345's main outputs. Both of
these outputs are fully floating, and their shields may be floated relative to
earth ground by up to ±40V. Both outputs also have a 50Ω output impedance. If the outputs are terminated into high impedance instead of 50Ω the
signal levels will be twice those programmed (the FUNCTION output may
also show an increase in waveform distortion). The programmed waveform
comes from the FUNCTION output, while the SYNC output generates a TTL
compatible (2.5 V into 50Ω) signal that is synchronous with the function out-
put. The SYNC signal is suppressed if the function is set to NOISE or
BURST modulation. If the function is set to ARB the SYNC signal is a 25ns
negative going pulse at the start of each waveform.
2-9
Function Setting
FUNCTION SELECTION
The DS345's output function is selected using the FUNCTION UP/DOWN arrow keys. Simply press the keys until the desired function LED is lit. If the
programmed frequency is outside of the range allowed for the selected function, an error message will be displayed and the frequency will be set to the
maximum allowed for that function. If modulation is enabled and the modulation type or parameters are incompatible with the new function, an error message will be displayed and the modulation will be turned off (the parameters
will not be altered).
Ramps
Ramp functions usually ramp up in voltage, however, downward ramps may
be programmed with the output invert function (see AMPLITUDE section).
Arbitrary Functions
Arbitrary functions may be created on a computer and downloaded to the
DS345 via the computer interfaces, or they may be created using the
DS345's front panel editing functions. Arbitrary waveforms normally repeat
continuously, single triggering and burst triggering of arbitrary waveforms is
accomplished using the DS345's BURST modulation function. (See the ARBITRARY WAVEFORM EDITING section for more detail.)
FREQUENCY
To display the DS345's output frequency press [FREQ]. The frequency is always displayed in units of Hz. The DS345 has 1 µHz frequency resolution at
all fre
quencies, for all functions. The maximum frequency depends on the
Function
Frequency Range
Sine
1 µHz → 30.200000000000 MHz
Square
1 µHz → 30.200000000000 MHz
Triangle
1 µHz → 100,000.000000 Hz
Ramp
1 µHz → 100,000.000000 Hz
Noise
10 MHz White Noise (fixed)
Arbitrary
0.002329Hz → 40.0 MHz sampling
function selected as listed below:
Frequency is usually displayed by the DS345 with 1 mHz resolution. However, if the frequency is below 1 MHz and the microhertz digits are not zero the
DS345 will display the frequency with 1 µHz resolution. At frequencies greater than 1 MHz the digits below 1 mHz cannot be displayed, but the frequency
still has 1 µHz resolution and may be set via the computer interfaces or by
using the MODIFY keys with a step size less than 1 mHz.
If the function is set to NOISE the character of the noise is fixed with a band
limit of 10 MHz. The frequency is not adjustable and the FREQ display will
read "noise" instead of a numerical value.
If the function is set to ARB the frequency displayed is the
sampling fre-
quency
of the arbitrary waveform. This number is independent of the usual
frequency; it is the dwell time that the DS345 spends on each point in an arbitrary waveform. This sampling frequency must be an integer submultiple
of
the the 40 MHz clock frequency. That is, 40 MHz/N where N = 1,2,3... 234-1
(40 MHz, 20 MHz, 13.3333 MHz, 10 MHz, ...). The DS345 will spend
2-10
Function Setting
1/
Fsample
on each point. When a new sampling frequency value is entered
the DS345 will round the value to the nearest integer submultiple of 40 MHz.
Note that the frequency for the standard functions is
never
rounded.
Setting the Frequency
To set the frequency of any function simply type a new value on the keypad
and complete the entry with the appropriate units (Hz, kHz, or MHz). The
MODIFY keys may be used to increase or decrease the frequency by the current step size. Press [STEP SIZE] key to display and change the step size.
AMPLITUDE
Pressing [AMPL] displays the amplitude of the output function. The amplitude
may be set and displayed in units of Vpp, V
rms
, and dBm. The current units
are indicated by the LEDs at the right of the display. The amplitude range is
limited by the DC offset setting since |V
ac peak
| + |Vdc| ≤ 5 V. If the DC offset
is zero the amplitude range for each of the functions is shown below:
note
: The rms and dBm values for NOISE are based on the total power in the
output bandwidth (about 10 MHz) at a given peak to peak setting.
V
pp
V
rms
dBm (50Ω)
Function
Max.
Min.
Max.
Min.
Max.
Min.
Sine
10V
10 mV
3.54V
3.54 mV
+23.98
-36.02
Square
10V
10 mV
5V
5 mV
+26.99
-33.0
Triangle
10V
10 mV
2.89V
2.89 mV
+22.22
-37.78
Ramp
10V
10 mV
2.89V
2.89 mV
+22.22
-37.78
Noise
10V
10 mV
2.09V
2.09 mV
+19.41
-40.59
Arbitrary
10V
10 mV
n.a.
n.a.
n.a.
n.a.
Arbitrary function amplitude may
only
be set in units of Vpp. The output sig-
nal will briefly go to zero as the output attenuators are switched.
The units of the amplitude display may be switched between Vpp, V
rms
, and
dBm without changing the actual amplitude by pressing the corresponding
units
key. When the DS345 is switched from one function to another the
peak-to-peak amplitude is held constant. If the DC offset is zero, the amplitude may be set with three digits of resolution. If the DC offset is not zero the
larger of the amplitude and the offset determines the resolution of both parameters. The amplitude display is automatically adjusted such that all of the
digits that may be changed are displayed.
Output Inversion
For ramp and arbitrary functions the DS345's output may be inverted. This is
useful for turning positive ramps into negative ramps, or inverting arbitrary
waveforms. Pressing [AMPL] two times displays the invert enable option.
Use the UP/DOWN MODIFY keys to enable or disable the inversion.
D.C. Only
The output of the DS345 may be set to a DC level by entering an amplitude
of 0V. When the amplitude is set to zero the A.C. waveform will be off and
the DS345 may be used as a DC voltage source. If the amplitude is zero the
display will read "no AC" when the units are set to dBm.
TTL Settings
Pressing [SHIFT][TTL] sets the output amplitude and offset to TTL values.
2-11
Function Setting
TTL levels are 5 V
pp
with a 2.5V offset (the output will swing between 0 and
+5V).
ECL Settings
Pressing [SHIFT][ECL] sets the output amplitude and offset to ECL values.
ECL levels are 1 Vpp with a -1.3V offset (the output will swing between -1.8V
and -0.8V).
DC OFFSET
The DC offset may range between ±5V, but is restricted such that |V
ac peak
|
+ |Vdc| ≤ 5 V. When [OFFST] is pressed a new value may be entered using
any amplitude unit key, the Vpp indicator LED will be lit . When the offset is
changed the output signal will
briefly go to zero as the output attenuators are
switched. If the amplitude is zero, the offset may be set with three digits of
resolution. If the amplitude is not zero the larger of the amplitude and offset
determines the resolution of both parameters. The offset display is automatically adjusted such that all of the digits that may be changed are displayed.
PHASE
Press [PHASE] to display and modify the phase of the FUNCTION output.
Phase is always measured with respect to the internal timebase,
not
the
SYNC output. The phase may be changed with the keypad and the DEG
unit
key, or using the MODIFY keys. The range of the phase setting is
±7199.999° and may be set with 0.001° resolution. If the function is set to
NOISE, ARB, or modulation is enabled in SWEEP, FM, or PM modes the
phase cannot be changed and the message "no Phase" will be displayed. In
BURST modulation mode the PHASE function will set the waveform phase
at the start of the burst. This is quite useful for starting the burst at a particular point in the waveform.
Zero Phase
The current phase may be assigned the value zero by pressing [SHIFT]
[REL=0]. Subsequent changes to phase will be relative to this value.
2-12
SWEEPS AND MODULATION
LIN SWP SINGLE MOD/SWP
SWEEP
ON/OFF
BURST
RATE
BRST CNT
SWP CF
SPAN
(DEPTH)
STOP f
START
FREQ
ARB
TRIG
FM
AM (INT)
LOG SWP
m
I
Introduction
This section of the manual describes the DS345's modulation capabilities.
The DS345 has extremely powerful and flexible built-in modulation functions.
It is capable of AM (both simple and double sideband suppressed carrier
(DSBSC)), FM, PM, tone bursts, and frequency sweeps. The modulation
waveform may be a sine, square, ramp, or triangle wave. Frequency can be
swept up or down at a linear or logarithmic rate. A built-in trigger generator allows triggering of single sweeps and bursts. For additional flexibility the
DS345 can also modulate the output waveform with an arbitrary pattern of
amplitude, frequency, or phase values.
SWEEP/MODULATE
MODULATION ON/OFF The SWEEP ON/OFF key enables the DS345's modulation functions. Press-
MODULATION TYPE The type of modulation is selected using the MODULATION TYPE [UP/
MODULATION WAVEFORM The waveform of the modulating function is selected with MODULATION
ing the key toggles the modulation status. When modulation is on the
[MOD/SWP] LED will light. When modulation is enabled the modulation type
and modulation parameters are checked for consistency with the selected
output function. If the selected modulation is illegal (for example, FM frequency out of range for the function) the DS345 will display an error message and
not enable the modulation. The erroneous value must be changed before the
modulation is turned on.
DOWN] arrow keys. Most of the output functions can be modulated by any
type of modulation. However, NOISE can only be modulated by the external
AM input, and ARB waveforms can only be modulated by AM and BURST
modulations. If an invalid choice is selected the message "funct error" is displayed.
WAVEFORM UP/DOWN arrow keys. If no LEDs are lit the selected modulation type has no associated waveform (BURST, for example, has no modulation waveform). Not all modulation types may use all modulation waveforms.
The allowable combinations are listed on the following page. Note that ARB
modulation waveforms can only be downloaded via the computer interfaces.
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