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: [phone] • Fax: [phone] www.thinkSRS.com • e-mail: [e-mail]

Copyright© 1999

All Rights Reserved

Revision 1.6 • 10/99

Stanford Research Systems

DS345 SYNTHESIZED FUNCTION GENERATOR

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

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

DS345 SYNTHESIZED FUNCTION GENERATOR

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

iii

DS345 SYNTHESIZED FUNCTION GENERATOR

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)

vi

DS345 SYNTHESIZED FUNCTION GENERATOR

Safety and Preparation for Use

WARNING: Dangerous voltages, capable of causing death, are present in this instrument. Use extreme caution whenever the instrument covers are removed.

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.

v

DS345 SYNTHESIZED FUNCTION GENERATOR

vi

SPECIFICATIONS

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 |Vac peak| + |Vdc|

≤ 5 V)

Vpp

Vrms

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

1µHz

Square:

100 kHz

20 MHz

30.2 MHz

10Vpp

±3 %

±6%

±15%

5Vpp

±5%

±8%

±18%

0.01Vpp

Triangle, Ramp, Arbitrary:

±3%

> 5Vpp

±5%

< 5Vpp

vii

Specifications

DC OFFSET
Range:	±5V (limited such that |Vac 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 s 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 queried 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
ATTL	VP (Vpp), VR (Vrms), or DB (dBm). Example: AMPL 1.00VR sets 1.00 Vrms.
	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,
INVT(?)i	5= arbitrary.
	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 % modu-
FDEV(?) x	lation.
	Sets the FM span to x Hz.
MDWF(?) i	Sets the modulation waveform. 0 = single sweep, 1 = ramp, 2 = triangle, 3 = sine,
MENA(?) i	4 = square, 5 = arbitrary, 6 = none.
	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
MTYP(?) i	freq, 3 = span.
	Sets the modulation type. 0 = lin sweep, 1 = log sweep, 2 = AM, 3 = FM, 4 = PM,
PDEV(?) x	5 = Burst.
	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.

Status Byte Definitions			Standard Event Status Byte
Serial Poll Status Byte			bit	name	usage
			0	unused
bit	name	usage	1	unused
			2	Query Error	set on output queue overflow
0	Sweep Done	set when no sweeps in progress	3	unused
1	Mod Enable	set when modulation is enabled	4	Execution Err	set on error in command execu-
2	User SRQ	set when the user issues a front			tion
		panel SRQ	5	Command Err	set on command syntax error
3	DDS	set when an unmasked bit in DDS	6	URQ	set on any front panel key
		status byte is set			press
4	MAV	set when GPIB output queue is	7	PON	set on power on
		non-empty
5	ESB	set when an unmasked bit in std	DDS Status Byte
		event status byte is set
6	RQS	SRQ bit	bit	name	usage
7	No Command	set when there are no unexecuted	0	Trig'd	set on burst/sweep trigger
		commands in input queue	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

xii

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 excep-
	tional 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 fre-
	quency). Some parameters are labelled above the keys in light gray. To dis-
	play 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 re-
	turns the previous value. The current parameter value may also be increased
	or decreased with the MODIFY keys. Pressing the UP ARROW key will in-
	crease 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 dis-
	play 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. Press-
	ing [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 previ-
	ously 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)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 al-
		lowable output frequencies. There are no restrictions on minimum or maxi-
		mum 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 indi-
		cate 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].		This recalls the DS345's default settings.
2)	Press [AMPL] then [5][Vpp].		Set the amplitude to 5Vpp.
3)	Press [SWEEP MODE UP ARROW] twice.		Set the modulation type to linear sweep.
4)	Press [RATE] then [1][0][0][Hz].		Set the sweep rate to 100 Hz. The sweep will take
			10 ms (1/100Hz). Set the scope time base to
			1ms/div.
5)	Press [START FREQ] then [1][0][0][kHz].		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].	This recalls the DS345's default settings.
2)	Press [AMPL] then [5][Vpp].	Set the amplitude to 5Vpp.
3)	Press [FREQ] then [1][0][kHz].	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

Introduction	Direct Digital Synthesis (DDS) is a method of generating very pure wave-
	forms 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.
Traditional Generators	Frequency synthesized function generators typically use a phase-locked loop
	(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 resolu-
	tion 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 jit-
	ter 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.
Arbitrary Waveforms	Arbitrary function generators bypass the need for wave-shaping circuitry.
	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 fre-
	quency reference. Instead of using a counter to generate addresses, an ad-
	der is used. On each clock cycle, the contents of a Phase Increment Register
	are added to the contents of the Phase Accumulator. The Phase Accumula-
	tor output is the address to the waveform RAM (see diagram below). By
	changing the Phase Increment the number of clock cycles needed to step

Figure 1: Block diagram of SRS DDS ASIC

DDS ASIC

External Control

Modulation CPU

Modulation RAM

Fixed

Frequency
Reference	Phase		Phase	Waveform
	Increment	+
			Accumulator	RAM
	Register
			48 bits	16k points
	48 Bits

Direct Digital Synthesis

	Fixed
DAC	Frequency
	Filter

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

Modulation RAM

40MHz Clock

DDS345 ASIC

AM Input

Amplitude DAC

Waveform	Cauer Filter	x2
	12 bit

RAM DAC

10 MHz Bessel Filter

Sync

Output

Square Wave

Comparator

Function

Output

	Amplitude	Output	Attenuators
	Control	Amp

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 wave 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 7th 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

Front Panel Features

11		12

				STANFORD RESEARCH SYSTEMS		MODEL DS345 30MHz SYNTHESIZED FUNCTION GENERATOR
10			STATUS			Hz	dBm
			REM	SRQ
						DEG	Vrms
			ACT	ERR
						%	Vpp
			TIMEBASE
			EXT	ERR	FUNCTION FREQ AMPL OFFS PHASE	TRIG STEP SPAN RATE MRK STRT f STOP f MODULATION

OUTPUTS

FUNCTION

SWEEP/MODULATE

ENTRY

MODIFY

SYNC

TRIG'D

LIN SWP

SINGLE

MOD/SWP

SHIFT

ARB EDIT

DEFAULTS

CALIBRATE

LOG SWP

9

FREQ

FM

SWEEP

SHIFT

STO

RCL

CLR

DEG

AM (INT)

ON/OFF

%

NOISE

TTL

Φ m

BRST CNT

GPIB

SRQ

RS232

DATA

TTL

+/-

7

8

9

MHz

ARB

AMPL

BURST

ARB

RATE

dBm

FUNCTION

ECL

TRIG

SWP CF

MRK START

MRK STOP

MRK CF

MRK SPAN

LOCAL

8

OFFST

SPAN

.

4

5

6

kHz

STEP

(DEPTH)

Vrms

SIZE

REL=0

STOP f

TRIG SOURCE TRIG RATE

MRK=SPAN

SPAN=MRK

ON/STBY

40V max.

Ω

PHASE

START

0

1

2

3

Hz

50

FREQ

Vpp

2

1

	7	6	5	3	4
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 asso-
	ciated 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 be-
	tween different menu selections (ie., trigger source). Sometimes the parame-
	ter 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 typ-
	ing error may be corrected by using the CLR key. The +/- key may be select-
	ed 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

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 amplitude 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 mes-
	sage will be displayed and modulation will not be turned on. Some modula-
	tion 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 be-
	yond 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 al-
	lowed 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 in-
	creased distortion. The shield of this output may be floated up to ±40V rela-
	tive 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 re-
		turns 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 dis-
	played you can return to the normal operation by pressing any key.

2-6

DS345 FEATURES

12) Units LEDs	These LEDs indicate the units of the displayed value. If no LED is lit the num-
	ber displayed has no units.

Rear Panel Features

1

2

3

INPUTS

TRIGGER	AM(EXT)	TIMEBASE
TTL	0-5V	10MHz
	OUTPUTS
TRIGGER	MODULATION	10MHz
TTL	0-5V	1V
SWEEP	MARKER	BLANK/LIFT
0-10V	TTL	TTL

WARNING: No user serviceable parts inside.

!Refer to operation manual for safety notice. For use by qualified laboratory personnel only.

FUSE: 3/4A (100/120VAC) or 3/8A (220/240VAC)

IEEE-488 STD PORT (GPIB)									RS232 (DCE, 8d, 0p, 2s bits)

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 out-
	put to -100% of the setting. The 0 to 5V range is used for normal AM opera-
	tion, 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 in-
	put is tied to the shield of the function output and may be floated up to ±40V
	relative to earth ground.
	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 inter-
	nal 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 func-
	tion. 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 be-
	gins, and goes low when it ends. This may be used to synchronize an exter-
	nal 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 out-
	put 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 pari-
	ty, 2 stop bits and 300 and 19.2k Baud. The shield of this connector is
	connected to earth ground.

2-8

DS345 OPERATION

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 ex-
	plains 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 ini-
	tiate 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, (press-
	ing any key will erase the error message).

SETTING THE FUNCTION

SYNC			TRIG'D
			FREQ
		NOISE	TTL
	TTL
		ARB	AMPL
FUNCTION			ECL
			OFFST
			REL=O
40V max	50 Ω		PHASE

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 impe-
	dance. 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 ar-
	row 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 func-
	tion, 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 modula-
	tion type or parameters are incompatible with the new function, an error mes-
	sage 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 AR-
	BITRARY WAVEFORM EDITING section for more detail.)
FREQUENCY	To display the DS345's output frequency press [FREQ]. The frequency is al-
	ways displayed in units of Hz. The DS345 has 1 µHz frequency resolution at
	all frequencies, 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. Howev-
	er, 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 great-
	er 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 ar-
	bitrary 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 cur-
		rent 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, Vrms, 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 |Vac 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.
			Vpp		Vrms		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, Vrms, 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 ampli-
		tude 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 pa-
		rameters. 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 Vpp 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 |Vac 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 automati-
	cally 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 particu-
	lar 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

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

LIN SWP		SINGLE	MOD/SWP
LOG SWP
				SWEEP
AM (INT)
				ON/OFF
FM
			BRST CNT
I m
		ARB		RATE
BURST
		TRIG
				SWP CF
				SPAN
				(DEPTH)
				STOP f
				START
				FREQ

MODULATION ON/OFF	The SWEEP ON/OFF key enables the DS345's modulation functions. Press-
	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 frequen-
	cy 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.
MODULATION TYPE	The type of modulation is selected using the MODULATION TYPE [UP/
	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 dis-
	played.
MODULATION WAVEFORM	The waveform of the modulating function is selected with MODULATION
	WAVEFORM UP/DOWN arrow keys. If no LEDs are lit the selected modula-
	tion type has no associated waveform (BURST, for example, has no modula-
	tion 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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