Stanford Research Systems DS335 Service manual

MODEL DS335
Synthesized Function Generator
1290-D Reamwood Avenue
Sunnyvale, California 94089
Phone: (408) 744-9040 • Fax: ( 408) 744- 9049
email: info@t hink S RS.c om • www.thinkSRS.com
Copyright © 1993 by SRS, Inc.
All Rights Reserved.
DS335 Synthesized Function Generator
Table of Contents
Table of Contents i
Condensed Information
Safety and Use iii SRS Symbols iv Specifications v Abridged Command List ix
Getting Started
Introduction 1-1 CW Function Generation 1-1 Frequency Sweep 1-2
Operation
Introd uc tion to DDS 2-1 DS335 Features 2-5
Front Panel Featur es 2-5 Rear Panel Features 2-7
Function Setting 2-9
Setting the Function 2-9
Frequency 2-9 Amplitude 2-9 DC Offset 2-11
Sweeps/FSK 2-13
Frequency Sweeps 2-13
Sweep Type 2-13 Sweep Frequencies 2-14 Sweep/FSK Output 2-14
FSK Intput 2-14
Instrument Setup 2-17
Default Sett ings 2-17
Store and Recall 2-17 GPIB and RS232 Setup 2- 17 Self-Test 2-18
Setup Control Commands 3-6 Status Report ing Commands 3-6 Test and Calibration Commands 3-7 Status Byte Definitions 3-8
Programming Examp les 3-11
Introduction 3-11 GPIB and C Example 3-12 RS232 and BASIC example 3-13
Test and Calibration
Troubleshooting 4-1
Operation Err or Messages 4-1 Self-Test Error Messages 4-2
Performance Tests 4-5
Necessary Equip ment 4-5
Functional Tests 4-6
Front Panel Test 4-6 Self Tests 4-6 Sine Wave 4-6 Square Wave 4-6 Amplitude Flatnes s 4-7 Output Level 4-7
Performance Tests 4-8
Frequency Acc ur ac y 4-8 Amplitude Accurac y 4-8 DC Offset Accuracy 4-9 Subharmonics 4-9 Spurious Signals 4-10 Harmonic Distort ion 4-10 Phase Noise 4-11 Square Wave Rise Time 4-11 Square Wave Symmet ry 4-11
Programming
Programming the DS335 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 3-2
Function Output Commands 3-3 Sweep Control 3-4
Test Scorecard 4-13
Calibration 4-15
Introduction 4-15 Calibration Enable 4-15 Calbytes 4-15
Necessary Equip ment 4-19 Adjustments 4-19
Output Amplifier Bandwidth 4-19 Bessel Filter A djus tment 4-20
DS335 Synthesized Function Generator
ii Table of Contents
Calibration 4-20
Clock Calibration 4-20
DS335 Circuitry
Circuit Descript io n 5-1
Front Panel Board 5-1 Main Board 5-1
Microprocessor S y stem 5-1 Display and Keyboard 5-2 System DAC and S/H's 5-3 DDS ASIC and Memory 5-3 DDS Waveform DAC 5-4 DDS Output Filter s 5-5 Pre-Attenuator 5-5 SYNC Generator 5-5 Function Select ion 5-6 Output Amplifier 5-6 Output Attenuator 5-6
Option Board 5-7
Power Supplies 5-7 GPIB and RS232 Interfac es 5-7
Component Parts Li st 5-9 Schematic Circui t Diagrams Sheet No.
Front Panel
Keypad and LED Display 1/1
Main/Bottom PC Board
Microprocessor 1/8 Display, Keyboard and Cable 2/8 System DACs 3/8 DDS ASIC, Memory, and Sweep 4/8 DDS Waveform DAC and Filters 5/8 SYNC and Pre-Attenuat ors 6/ 8 Output Amplifier 7/8 Regulators and Att enuators 8/8
Option/Top PC Board
Power Supply and Cable 1/2 GPIB and RS232 Interfac es 2/2
Front Panel Compon ent Placement Main PC Board Component Placemen t Option Board Compon ent Placement
DS335 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 instru ment covers are remo ved.
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.
Safety and Preparation for Use iii
LINE VOLTAGE SELECTION
The DS335 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 sour ce, verify t hat t he LINE VOLTAGE SELECTOR card, located in the rear panel fuse holder, is set so that the correct ac input voltage value is vis ible.
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 t he board so that the des ired voltage is visible when it is pushed f irmly bac k into its slot. Rotate the fuse-pull lever back into its normal position and insert the corr ect 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 slow blow fuse and for 220V/240V, use a 1/2 Amp slow blow fuse.
LINE CORD
The DS335 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.
DS335 Synthesized Function Generator
iv SRS Symbols
DS335 Synthesized Function Generator
SPECIFICATIONS
FREQUENCY RANGE
Specifications v
OUTPUT
AMPLITUDE
Waveform Maximum Sine 3.1 MHz 1 µHz ±25ppm Square 3.1 MHz 1 µHz ± 25ppm Ramp 10 KHz 1 µHz ±25ppm Triangle 10 KHz 1 µHz ±25ppm Noise 3.5 MHz (Gaussian Weighting)
Source Im pedance : 50 Output may float up to ±40V (AC + DC) relat iv e to earth ground.
Range into 50 load (limited such that | V
Function Max. Min. Max. Min.
Sine 10V 50 mV 3.54V 0.02Vrms Square 10V 50 mV 5.00V 0.03Vrms Triangle 10V 50 mV 2.89V 0.01Vrms Ramp 10V 50 mV 2.89V 0.01Vrms Noise 10V 50 mV 1.62V 0.01Vrms
Freq Resolution Accuracy
| + |Vdc | 5 V)
ac peak
Vpp Vrms
Range into a high impedance load (limited s uc h that |V
Vpp Vrms
Function Max. Min. Max. Min.
Sine 20V 100 mV 7.07V 0.04Vrms Square 20V 100 mV 10V 0.05Vr m s Triangle 20V 100 mV 5. 77V 0.03V r m s Ramp 20V 100 mV 5. 77V 0.03V r m s Noise 20V 100 mV 3.24V 0.02Vrms
Resolution 3 digits Accuracy (with 0V DC Offset) , 50ΩΩΩ terminated
Sine: Accuracy
± 0.1 dB
Square: Accuracy
± 2%
Triangle, Ramp: Accur ac y
±2%
| + |Vdc| 10 V)
ac peak
DS335 Synthesized Function Generator
vi Specifications
DC OFFSET
Range: ±5V into 50 (limited such that | V
Limitation: |V Resolution: 3 digits
Accuracy: 1.2% of s etting (DC only)
WAVEFORMS
Sinewave Spectral P urity
Spurious (non-harmonic ) : -65 dBc to 1 MHz Phase Noise: - 60dB c in a 30 KHz band centered on the carrier, Subharmonic: -70 dBc
Harmonic Distort ion: Harmonically related s ignals will be les s than:
| + |Vdc | 5 V)
ac peak
±10V into hi-Z (limited such that | V
| 2xVpp in all cases
dc
| + |Vdc | 10 V)
ac peak
±0.8 mV to ±80 mV depending on AC and DC settings
-55 dBc to 3.1 MHz
exclusive of disc r ete spurious signals
Level Frequency Range
-60 dBc -50 dBc -40 dBc
DC to 100 KHz .1 to 1 MHz 1 to 3.1 MHz
Square Wa v e
Rise/Fall Time: < 15 nS ±5 nS (10 to 90%), at full output Asymmetry: < 1% of period + 3 nS Overshoot: < 5% of peak to peak amplitude at full out put
Ramps and Triangle
Rise/Fall Time 100 ±20 nS (3.5MHz Bessel Filter ) Linearity ±0.1% of full scale output Settling Time < 200 ns to settle within 0. 5% of f inal v alue at f ull output
FREQUENCY SWEEP
Type: Linear or Log, phase continuous Waveform: Up, down, up-down, single sweep Rate: 0.01 Hz to 1 kHz Span: 1 µHz to 3.1 MHz (10 kHz for triangle or ramp)
FREQUENCY-SHIFT KEYING (FSK)
Type: Internal r ate or External control, phase continuous Waveform: Sine, Square, Triangle, Ramp Rate: 0.01 Hz to 50 kHz (internal) Shift Span: 1 µHz to 3.1 MHz (10 kHz for triangle or ramp) External: TTL input, 1MHz maximum
DS335 Synthesized Function Generator
SYNC & SWP/FSK OUTPUTS
SYNC: TTL level, active with all functions SWP/FSK: TTL level, synchronous with internal Sweeps and FSK rates
TIMEBASE
Accuracy ±25 ppm (0 to 70° C) Aging 5 ppm/year
Optional Timebas e
Type: T em per ature Compensated Crystal Oscillator Stability: +/- 2.0 ppm, 0 to 50°C Aging: 5 ppm first year, 2 ppm per year t her eaft er
GENERAL
Interfaces RS232-C (300 to 9600 Baud, DCE) and GPIB. Weight 8 lbs.
Dimensions 8.5" x 3.5" x 13" (W x H x L) Power 25 Watts, 100/120/220/ 240 V ac 50/60 Hz
Specifications vii
All instrument functions can be controlled over t he interfaces.
DS335 Synthesized Function Generator
viii Specifications
DS335 Synthesized Function Generator
Abridged Command List ix
Abridged Command List
Syntax
Variables i,j are integer s. Variable x is a real number in int eger , 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 param eters are enclosed by {}.
Function Output Control Commands AECL Set s the output amplitude/offs et t o E C L levels (1V pp, -1.3V offset).
AMPL(?) x Sets the output amplitude to x. x is a value plus units indicator. The units c an
be VP (Vpp), VR (Vrms). Example: AM P L 1.00VR s ets 1.00 Vrms.
ATTL Sets the output am plitude/offset to TTL levels (5 Vpp, 2. 5 V offset). FREQ(?) x S ets the output frequency t o x Hz. FUNC(?) i Sets the output function. 0 = sine, 1 = square, 2 = triangle, 3 = ram p,
4 = noise.
INVT(?)i Sets the output inversion on (i=1) or off (i=0). Used with the ramp function. KEYS(?) i Simulates a key pr ess or r eads the m ost r ec ently pressed key. OFFS(?)x Sets the output offset to x volts. SYNC(?) i Turns the Sync output on (i=1) or off (i=0). TERM(?) i Sets the output source impedance to 50 (i=0), Hi-Z (i=1).
Sweep control command s FSEN(?) i Enables FSK on (i=1) or off (i=0). Valid only if SDIR2 is sent first.
*TRG Triggers single sweeps if in single trigger mode. SDIR(?)i Sets the sweep direction 0 = Ramp, 1 = Triangle, 2 = FSK. SPFR(?) x Sets the sweep stop frequency to x Hz. SRAT(?) x Sets the sweep rate to x Hz. STFR(?) x Sets the sweep start frequency t o x Hz. STYP(?) i Sets the sweep type. 0 = linear sweep, 1 = logarithmic sweep. SWEN(?) i Turns sweeps on (i=1) or off (i=0). TSRC(?) i Sets the trigger s our c e for s weeps . 0 = single, 1 = internal sweep rate.
Setup Control Command s *IDN? Ret urns the device identif ic ation.
*RCL i Recalls stored setting i. *RST Clears instrument to default settings. *SAV i Stores the current settings in storage location i.
Status Reporting Co mmand s *CLS Clears all status r egisters.
*ESE(?) j Set s /reads the standard status byte enable register. *ESR? {j} Reads the standard status regist er, or just bit j of register. *PSC(?) j Sets the power on status clear bit . T his allows SRQ's on power up if desired. *SRE(?) j Sets/reads the serial poll enable regis ter. *STB? {j} Reads the serial poll regis ter, 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 regist er.
DS335 Synthesized Function Generator
x Abridged Command List
Hardware Test Control *TST? Starts self-test and returns status when done.
Status Byte Definitions
Serial Poll Status Byte bit name
0 Sweep Done set when no sweeps in progress 1 Sweep Enable set when sweep or FSK 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 ar e no unex ecuted commands in input queue
Standard Event Status Byte bit name
0 unused 1 unused 2 Query Error s et on output queue overflow 3 unused 4 Execution Err set on err or 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
usage
usage
bit name 0 Trig'd set on sweep trigger 1 Not in use 2 Not in use 3 Not in use 4 Warmup set when the DS335 is warmed up 5 Test Error set when self test fails 6 Not in use 7 mem err set on power up memory error
usage
DS335 Synthesized Function Generator
Getting Started 1-1
Getting Started
Introduction This section is designed to f amiliarize you with the operation of the DS335
Synthesized Function Generator. The DS335 is a powerful, flexible generator capable of producing both continuous and swept waveforms of exceptional purity and resolution. The DS335 is also relatively sim ple to use, and the following examples will lead you step-by-st ep through some typical uses.
Data Entry Setting t he DS335's operational par amet ers is done by pres sing the key wit h
the desired parameter's name on it (FREQ, for example, to set the frequency). The c ur r ent value will be dis play ed. Some of the parameters are labeled above the keys in light gr ay. To display those values first press the SHIFT key and then the labeled key ([SHIFT][ STOP FREQ], for example, to display the type of wavef orm sweep set). Values ar e changed by the DATA ENTRY keys. To directly enter a value simply type t he new value using the keypad and complete the entry by hitting one of t he UNITS key s. If the v alue has no particular unit s any of the UNIT S keys may be used, other wise select the appropriate units key. If an error is made, pressing the corresponding function key will backspace the cursor. If the key is pressed repeat edly the display will eventually show the previous value. For example, if a new frequency is being entered and the wrong numeric key is pressed, then pressing the FREQ key will backspace the cursor. If the FREQ key is pressed until the new entry is erased, then t he last valid frequency v alue will be displayed. The current parameter value may also be incremented or decremented using the UP and DOWN ARROW keys. Pressing the UP ARROW key will increment the flashing digit value by one, while press ing the DOWN ARROW key will decrement the flashing digit value by one. If the parameter value cannot be incremented or decremented, the DS335 will beep and display an error message. Pressing [SHIFT][UP ARROW] or [SHIFT][DOWN ARROW] changes the position of the blinking digit.
CW Function Gene r a t io n Our first example demonstrates a CW waveform using the DS335's data
entry functions. Connect the front panel FUNCTION output to an oscilloscope, ter minating the output into 50 ohms. Turn the DS335 on and wait until the message "TEST PASS" is displayed (if the self tests fail, refer to TROUBLESHOOTING section of the manual).
1) Press [SHIFT][+/-]. This rec alls the DS335's default settings.
2) Press [AMPL]. Then press [5][Vpp]. Displays the amplitude and sets it to 5 Vpp. The scope should show a 5 Vpp 1 MHz sine wave.
3) Press [FUNC DOWN ARROW] twice. The function should change to a square wave and then a triangle wave. The DS335 automatically performs a frequency adjustment to match the maximum triangle frequency (10kHz ) .
4) Press [FREQ] and then [1][kHz]. Displays the frequency and sets it to 1 kHz. The scope should now display a 1 kHz triangle wave.
5) Press [UP ARROW]. The frequency will increment to 1.0001 kHz. The flashing digit indicates a st ep s iz e of 0. 1 Hz.
DS335 Synthesized Function Generator
1-2 Getting Started
6) Press [SHIFT UP ARROW] twice. Observe that the blinking digit is shifted twice to the left indicating a step size of 10 Hz.
7) Press [UP ARROW] thr ee times . We've changed t he output frequency to 10.0301 kHz.
Frequency Sweep The next example demonstrat es a linear frequency sweep. The DS335 c an
sweep the output frequency of any function over the entire range of allowable output frequencies. There are no restrictions on minimum or maximum sweep span. The sweep is phase continuous and may range from 0.01Hz to 1000 kHz.
Attach the FUNCTION out put BNC to t he os cilloscope, terminating the output into 50 ohms. S et the scope to 2V/div. Attach the SWEEP rear-panel BNC to the scope and set to 2V/div. The s cope should be set to trigger on t he rising edge of this s ignal.
1) Press [SHIFT][+ /-]. This recalls the DS335's default s ett ings.
2) Press [AMPL] then [5][ V pp]. Sets the amplitude to 5Vpp.
3) Press [SHIFT] [STO P FREQ]. Verify linear sweep. "Lin" should be blinking now.
4) Press [SWE EP RATE] then [1][0][0] [Hz ]. Set the sweep rate t o 100 Hz . The s weep will take 10 ms (1/100Hz). Set t he scope time base to 1ms/div.
5) Press [START FREQ] then [1][0][0][kHz]. Set the sweep start frequency to 100 kHz.
6) Press [STOP FREQ] then [1] [MHz ]. Set the stop frequency to 1 MHz.
7) Press [SHIFT][START FREQ]. The SWP LED will light, indicating that the DS335 is sweeping. The scope should show the SWEEP output as a TTL pulse synchronous with the start of the sweep. The FUNCTION output is the swept sine wave. The DS335 also displays the option to switching to single shot sweeps at this time. Pressing the up or down arrows at this time switches the sweeps to single shot. Pressing [SHI FT][START F REQ] triggers one sweep.
DS335 Synthesized Function Generator
Introduction 2-1
Introduction to Direct Digital Synthesis
Introduction Direct Digital Synthesis (DDS) is a method of generating very pure
waveforms with extraordinary f requency resolution, low frequency switching time, crystal clock-like phase noise, and flex ible s weeping c apabilities. A s an introduction to DDS let's review how traditional funct ion generators work.
Traditional Generator s Frequency synthesized function generators ty pically use a phase-lock ed 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 resolution PLL so the frequenc y resolution is usually limited to about 1:10 (some sophistic ated fractional-N PLLs do have much higher r es olution). Due to the action of the PLL loop filter, these synthesizers typically have poor phase jitter and fr equency switching respons e. In addition, a separate wave­shaping circuit is needed f or each t ype of waveform desired, and these of ten produce large amounts of waveform distort ion.
DDS DDS works by generating address es to a waveform ROM to produce dat a 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 ROM (see diagram below). By changing the Phase Increment the number of clock cycles needed to step through the entire waveform ROM changes, thus changing the output frequency.
6
Figure 1: Block diagram of S RS DDS ASIC
Frequency changes now can be accomplished phase continuously in only one clock cycle. And the fixed clock eliminates phase jitter, requiring only a simple fixed fr equenc y anti-aliasing filter at t he output.
The DS335 uses a custom Application Specif ic Integrated Circuit (ASIC) to implement the address generation in a single component. The frequency resolution is equal to the resolution with which the Phase Incr ement can be set. In the DS335, the phase registers are 48 bits long, resulting in an impressive 1:10 control CPU that operat es on the Phase Accumulat or, P hase Inc rement, and external circuit ry to allow digital synthesis and contr ol of waveform sweeps. The Modulation CPU uses data stored in the Modulation RAM to produce frequency sweeps. All modulation par ameters, such as rate, and frequency deviation, are digitally programmed.
14
frequency resolution. The ASIC also contains a modulation
DS335 Synthesized Function Generator
2-2 Introduction
DS335 Description
DDS gives the DS335 greater flexibility and power than conventional synthesizers without the drawbacks inherent in PLL designs.
Figure 2: DS335 Bloc k Diagram
A block diagram of the DS335 is shown in Figure 2. T he heart of the DS335 is a 10 MHz crystal clock. The 10 MHz clock controls the DDS ASIC, waveform ROM, and high-speed 12bit DAC. Sampling theory limits the frequency of the waveform output from the DAC to about 40% of 10 MHz, or 3 MHz. The 48 bit length of the ASIC's PI R' s s ets the frequency resolution to about 36 nHz. These parameters and the DA C's 12 bit resolution define the performance limits of the DS335.
The reconstruction filter is key to accurately reproducing a waveform in a sampled data system. The DS335 contains two separate filters. For sine wave generation the output of the DAC goes through a 7 while ramps, and triangles pass instead through a 3.5 MHz 5
th
order Cauer filter,
th
order Bess el filter. The Cauer filter has a c utoff frequency of 3.4 MHz and a stopband attenuation of 86 dB, and includes a peaking circuit to correct for the sin(x)/x amplitude response characteristic of a sampled system. This filter eliminates any alias frequencies from the waveform output and allows generation of extr emely pure sine waves. 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.
The output from the filter passes thr ough pre-amplif ier attenuat ors wit h a 0 to 14 dB range. The attenuators are followed with a wide bandwidth power amplifier that outputs a 10 V peak-to-peak into a 50 ohm load with a ris e time of less than 15 ns. The output of the power am plifier passes through a series of four step attenuators (2, 4, 8, and 16 dB) that set the DS335's final out put
DS335 Synthesized Function Generator
Introduction 2-3
amplitude. The post amplifier attenuators allow internal signal levels to remain as large as possible, minimizing output nois e and s ignal degr adation.
Square waves and waveform sync signals are generated by discriminating the function waveform with a high-speed comparator. The output of the comparator pass es to the SYNC OUTPUT and, in the c ase of square waves, to the amplifier input . G enerating 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.
DS335 Synthesized Function Generator
2-4 Introduction
DS335 Synthesized Function Generator
Front Panel Features
Features 2-5
1) Power Switch The power switch turns the DS335 on and off. The DS335 has a battery
backed up system RAM that remembers all inst rument settings.
2) Data Entry Keys The numeric keypad allows for direct entry of the DS335's parameters. To change a parameter value s im ply type the new value. Ent r ies are terminat ed by the UNITS keys. A typing error may be corrected by pressing the corresponding function key. For example, if the wrong numeric key is pressed while entering a new frequency, pressing the [FREQ] key will backspace over the last entered digit. If there are no digits left, the current frequency value is displayed. The [+/-] key may be selected at any time during numeric entry .
3) Units Keys The UNIT keys are used t o terminate numer ic entries. Simply press the key with the desired units to enter the typed value. Some parameters have no particular units and any of the unit keys may be used.
The unit keys also increase and decrease the num eric value in the DS335's display. Pressing t he [UPARROW] key adds one to the flashing digit value, the [DOWN ARROW] key subtracts one from the flashing digit value. To change the position of the flashing digit, press [SHIFT] [LEFT ARROW] or [SHIFT] [RIGHT AR ROW]. A few of the display menus have more t han one parameter displayed at a time. The [SHIFT][LEFT ARROW] and [SHIFT][RIGHT ARROW ] key s select between left and right.
4) Shift Key The shift key s elects the function printed abov e the keys. Pressing [SHIFT] and then the desired key to select the specific function (for example [SHIFT][50] sets the source impedance to 50. When the SHIFT key is pressed the SHIFT LED will light. Pressing [SHIFT] a second time will deactivate shif t m ode.
DS335 Synthesized Function Generator
2-6 Features
5) Sweep Key These keys control t he different s weep parameters inc luding: St art and Stop
Frequencies, Sweep Rate, Continuous or Single Sweep, Linear or Log Sweep, Unidirectional or Bidirectional Sweeps, and FSK.
6) Function Keys These keys control the main function output. The Func [DOWN ARROW] key and [SHIFT][UP ARROW] key select between the output functions. If the output frequency is set beyond the range allowed for a waveform (> 10kHz for triangle and ram p) an error message will be displayed and the f requency will change to the maximum allowed for that function.
7) Main Function BNC This output has an impedance of 50. The shield of this output may be floated up to ±40V relative to earth ground.
8) Sync Output BNC This output is a TTL squar e wave synchronized to the main function out put and has a 50 output impedance. The shield of this out put may be float ed
up to ±40V relative t o earth gr ound.
9) Status LEDs These four LEDs indicate the DS335's st atus. They are: name function
REMOTE The DS335 is in GPIB remote state. The [3] key r eturns local
control. GPIB Flashes on GPIB activity. RS232 F las hes on RS 232 activity. ERROR Flashes on an error in the execution of a remote or local
command including range error s .
10) Parameter Displ ay The 8 digit display shows the v alue of the c ur r ently displayed parameter. The LEDs below in the DISPLAY section indicate which parameter is being displayed. Error messages also appear on the display. When an error message is displayed you c an return to the normal display by pressing any key.
11) Units LEDs The Units LEDs indicate the units of the displayed param eter . If no LED is lit the value has no units. The SWP LED indicates that a sweep or FSK is in progress.
12) Load Impedance LEDs These LEDs indicate the load impedance value as set by the user. The amplitude and offset display values will change according to the load impedance setting.
DS335 Synthesized Function Generator
Rear Panel Features
Features 2-7
1) Power Entry Module This contains the DS335's fuse and line voltage select or. Use a 1 amp slow
blow fuse for 100/120 volt operation, and a 1/2 amp fuse for 220/240 volt operation. To set the line volt age selector for the correct line voltage, firs t remove the fuse. Then, remove the line voltage select or card and rotate t he card so that the correct line voltage is dis played when the card is reinsert ed. Replace the fuse.
2) Sweep/FSK Outpu t This output generates a TTL pulse that is synchronous with the DS335's frequency sweep. When the DS335 is in FSK mode, the output voltage reflects the present frequency at the FUNCTION output BNC (TTL LOW = Start Frequency , TTL HIGH = Stop Frequency). The shield of this output is tied to that of the function output and may be floated up to ±40V relat ive to earth ground.
3) FSK Input The Fr equency-S hift Key ing input allows t he user to toggle between the st art frequency and the stop frequency. The BNC takes a TTL level input. When the input is low the st art frequency is active, and when the input is high the stop frequency is act i v e. This input is s am pled at 10 MHz.
4) GPIB Connector If the DS335 has t he optional GPIB/RS232 interface this c onnector is used for IEEE-488.1 and .2 compatible communications. The shield of this
connector i s connect ed to earth ground.
5) RS232 Connector If the DS335 has t he optional GPIB/RS232 interface this c onnector is used
for RS232 communication. The DS335 is a DCE and accepts 8 bits, no parity, 2 stop bits at between 300 and 9600 Baud. The shield of this
connector i s connect ed to earth ground.
DS335 Synthesized Function Generator
2-8 Features
DS335 Synthesized Function Generator
Function Setting 2-9
DS335 OPERATION
Introduction The following sections describe the operation of the DS335. The first section
describes the basics of setting t he function, frequenc y, amplitude, and off set. The second section explains sweeps and FSK. The third section explains storing and recalling setups, running s elf-t est and autoc alibration, and set ting the computer interfaces.
Power-On When the power is first applied t o the DS335 the unit will display its s erial
number and ROM version for about three seconds. Then, the DS335 will initiate a series of self-tests of the c ircuitry and stored data. The test should take about three seconds and end with the message "TST PA SS". If the self test fails the DS335 will display an err or message indicat ing the nat ure of the problem (see the TROUBLESHOOTING section for more details). The DS335 will still attem pt 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 DS335's main outputs. Both of
these outputs ar e f ully floating, and their shields may be floated relative to earth ground by up to ±40V. Both outputs also have a 50 output impedance. If the out puts are terminated into high impedance instead of 50W the signal levels will be twice those programm ed (the FUNCTION output may also show an increase in wavefor m dist ortion). The output im pedance should be set properly from the front panel using the [SHIFT][ 5] or [SHIFT][6] keys. Incorrect impedance matching may result in output voltages that do not correspond to the displayed amplitudes and offsets. For example, if the DS335 is set for a 50 Ohms source impedance and the output is connec ted to a scope without a 50 Ohms ter minator, then t he scope waveform will be twice the amplitude displayed on the DS335.The programmed waveform comes from the FUNCTION output , while the SYNC output generat es a T TL compatible (2.5 V into 50) signal that is synchronous with the function output. The SYNC signal is suppressed if the function is set to NOISE or ARB. The SYNC signal can be disabled and enabled with the [S HIF T] [0] and [SHIFT][.] keys.
FUNCTION SELECTION The DS335's output function is selected using the FUNCTION UP/DOWN
arrow keys. Simply press the keys until the desir ed function LED is lit. If the programmed frequency is outside of the range allowed for the selected
DS335 Synthesized Function Generator
2-10 Function Setting
function, an err or message will be displayed and the f requency will be set to the maximum allowed f or that function.
Ramps Ramp functions usually ramp up in voltage, downward ramps may be set
entering a negative amplit ude ( see AMPLITUDE section).
FREQUENCY To display the DS335's output frequency press t he [FREQ]. The frequency
units can be Hz, kHz, or MHz, and ar e indicated by the LE Ds on the r ight of the display. The DS335 has 1 µHz frequency resolution at all fr equencies, for all functions . The maximum frequenc y depends on the f unction selected as shown below.
Function Frequency Range
Sine Square Triangle Ramp
1 µHz 3.100000000000 MHz 1 µHz 3.100000000000 MHz 1 µHz 10,000.000000 Hz 1 µHz 10,000.000000 Hz
Noise 3.5 MHz White Noise (fixed)
Frequency is usually displayed by the DS335 with the highest resolution possible. However, if t he frequency is below 100 Hz, the DS335 will display the frequency wit h 1 µHz resolution. At frequencies greater than 1 MHz the digits below 0.1 Hz cannot be displayed, but the frequency still has 1 µHz resolution and may be set via the computer interfac es.
If the function is set to NOISE the charact er of the noise is fixed wit h a band limit of 3.5 MHz. The frequency is not adjus table and the FREQ display will read "noise" instead of a numerical value.
Setting the Frequency To set the frequency of any f unction simply t ype a new value on the k eypad
and complete the entr y with the appropriate units (Hz, kHz, or MHz). Also, the UP and DOWN arrow keys may be used to increm ent or decrement the frequency by adding or s ubtracting one from the flashing digit.
AMPLITUDE Press [AMPL] to display t he amplitude of the output func tion. T he amplitude
may be set and displayed in units of V
and V
pp
. The current units are
rms
indicated by the LEDs at the right of the display. The amplitude range is limited by the DC offset setting since |V
| + |Vdc| 5 V (into 50). If
ac peak
the DC offset is zero the amplitude range for each of the functions is shown below:
Note: The rms value for NOISE is based on the total power in the output bandwidth (about 3.5 MHz) at a given peak to peak setting.
Function Max. Min. Max. Min.
Sine 10V 50 mV 3. 54V 0.02Vrms Square 10V 50 mV 5.00V 0.03Vrms Triangle 10V 50 mV 2.89V 0.01Vrms Ramp 10V 50 mV 2. 89V 0.01Vrms Noise 10V 50 mV 1.62V 0.01Vrms
50ΩΩΩ Load Impedance
DS335 Synthesized Function Generator
Vpp Vrms
Function Setting 2-11
Vpp Vrms
Function Max. Min. Max. Min.
Sine 20V 0.1V 7.07V 0.04Vrms Square 20V 0.1V 10.0V 0.05Vrms Triangle 20V 0.1V 5.77V 0.03Vrms Ramp 20V 0.1V 5.77V 0.03Vrms Noise 20V 0.1V 3.24V 0.02Vrms
HIGH-Z Load Impedance
Output Inversion The DS335's output may be invert ed f or r amp functions. This is useful for
turning positive ram ps into negative ramps. E ntering a negative am plitude inverts the ramp out put.
D.C. Only The output of the DS335 may be s et to a DC level by entering an amplitude
of 0 V. When the amplitude is set to zero the A.C. waveform will be completely shut off and the DS335 may be used as a DC voltage source.
DC OFFSET When the [OFFS] key is pressed the DC offset is displayed and the V
pp
indicator LED will be lit. A new value may be entered numerically with any amplitude unit key. In general, the DC offset may range bet ween ±5V, but is restricted such that |V
| 10 V (into HIGH-Z). The DC offset is also restric ted such that |Vdc|
|V
dc
2 x V
. When the offset is changed, the out put signal will briefly go to zero
pp
| + |Vdc| 5 V (into 50 Ohms), or | V
ac peak
ac peak
| +
as the output attenuators are switched, and then back to t he set offset value.
SYNC ENABLE Pressing the [SHIFT] [.] key enables the SYNC OUT function. The
[SHIFT][0] disables the output by highly attenuating the output function signal.
DS335 Synthesized Function Generator
2-12 Function Setting
DS335 Synthesized Function Generator
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