Output Amplifier Bandwidth4-19
Bessel Filter A djus tment4-20
DS335 Synthesized Function Generator
ii Table of Contents
Calibration4-20
Clock Calibration4-20
DS335 Circuitry
Circuit Descript io n5-1
Front Panel Board5-1
Main Board5-1
Microprocessor S y stem5-1
Display and Keyboard5-2
System DAC and S/H's5-3
DDS ASIC and Memory5-3
DDS Waveform DAC5-4
DDS Output Filter s5-5
Pre-Attenuator5-5
SYNC Generator5-5
Function Select ion5-6
Output Amplifier5-6
Output Attenuator5-6
Option Board5-7
Power Supplies5-7
GPIB and RS232 Interfac es5-7
Component Parts Li st5-9
Schematic Circui t Diagrams Sheet No.
Front Panel
Keypad and LED Display1/1
Main/Bottom PC Board
Microprocessor1/8
Display, Keyboard and Cable2/8
System DACs3/8
DDS ASIC, Memory, and Sweep4/8
DDS Waveform DAC and Filters5/8
SYNC and Pre-Attenuat ors6/ 8
Output Amplifier7/8
Regulators and Att enuators8/8
Option/Top PC Board
Power Supply and Cable1/2
GPIB and RS232 Interfac es2/2
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.
Range into a high impedance load (limited s uc h that |V
VppVrms
FunctionMax.Min.Max.Min.
Sine20V100 mV7.07V0.04Vrms
Square20V100 mV10V0.05Vr m s
Triangle20V100 mV5. 77V0.03V r m s
Ramp20V100 mV5. 77V0.03V r m s
Noise20V100 mV3.24V0.02Vrms
Resolution3 digits
Accuracy (with 0V DC Offset) , 50ΩΩΩΩ 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 Ω (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
LevelFrequency 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)
Aging5 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
InterfacesRS232-C (300 to 9600 Baud, DCE) and GPIB.
Weight8 lbs.
Dimensions8.5" x 3.5" x 13" (W x H x L)
Power25 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
AECLSet s the output amplitude/offs et t o E C L levels (1V pp, -1.3V offset).
AMPL(?) xSets 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.
ATTLSets the output am plitude/offset to TTL levels (5 Vpp, 2. 5 V offset).
FREQ(?) xS ets the output frequency t o x Hz.
FUNC(?) iSets the output function. 0 = sine, 1 = square, 2 = triangle, 3 = ram p,
4 = noise.
INVT(?)iSets the output inversion on (i=1) or off (i=0). Used with the ramp function.
KEYS(?) iSimulates a key pr ess or r eads the m ost r ec ently pressed key.
OFFS(?)xSets the output offset to x volts.
SYNC(?) iTurns the Sync output on (i=1) or off (i=0).
TERM(?) iSets the output source impedance to 50Ω (i=0), Hi-Z (i=1).
Sweep control command s
FSEN(?) iEnables FSK on (i=1) or off (i=0). Valid only if SDIR2 is sent first.
*TRGTriggers single sweeps if in single trigger mode.
SDIR(?)iSets the sweep direction 0 = Ramp, 1 = Triangle, 2 = FSK.
SPFR(?) xSets the sweep stop frequency to x Hz.
SRAT(?) xSets the sweep rate to x Hz.
STFR(?) xSets the sweep start frequency t o x Hz.
STYP(?) iSets the sweep type. 0 = linear sweep, 1 = logarithmic sweep.
SWEN(?) iTurns sweeps on (i=1) or off (i=0).
TSRC(?) iSets 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 iRecalls stored setting i.
*RSTClears instrument to default settings.
*SAV iStores the current settings in storage location i.
Status Reporting Co mmand s
*CLSClears all status r egisters.
*ESE(?) jSet s /reads the standard status byte enable register.
*ESR? {j}Reads the standard status regist er, or just bit j of register.
*PSC(?) jSets the power on status clear bit . T his allows SRQ's on power up if desired.
*SRE(?) jSets/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(?) jSets/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
bitname
0Sweep Doneset when no sweeps in progress
1Sweep Enableset when sweep or FSK is enabled
2User SRQset when the user issues a front panel SRQ
3DDSset when an unmasked bit in DDS status byte is set
4MAVset when GPIB output queue is non- empty
5ESBset when an unmasked bit in std event status byte is set
6RQSSRQ bit
7No Commandset when there ar e no unex ecuted commands in input queue
Standard Event Status Byte
bitname
0unused
1unused
2Query Errors et on output queue overflow
3unused
4Execution Errset on err or in command execution
5Command Errset on command syntax error
6URQset on any front panel key press
7PONset on power on
DDS Status Byte
usage
usage
bitname
0Trig'dset on sweep trigger
1Not in use
2Not in use
3Not in use
4Warmupset when the DS335 is warmed up
5Test Errorset when self test fails
6Not in use
7mem errset on power up memory error
usage
DS335 Synthesized Function Generator
Getting Started 1-1
Getting Started
IntroductionThis 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 EntrySetting 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 nOur 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 SweepThe 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
IntroductionDirect 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 sFrequency 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.
DDSDDS 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 SwitchThe 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 KeysThe 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 KeysThe 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 KeyThe 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][50Ω] sets the source impedance to 50Ω. 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 KeyThese 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 KeysThese 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 BNCThis output has an impedance of 50Ω. The shield of this output may be
floated up to ±40V relative to earth ground.
8) Sync Output BNCThis output is a TTL squar e wave synchronized to the main function out put
and has a 50Ω output impedance. The shield of this out put may be float ed
up to ±40V relative t o earth gr ound.
9) Status LEDsThese four LEDs indicate the DS335's st atus. They are:
namefunction
REMOTEThe DS335 is in GPIB remote state. The [3] key r eturns local
control.
GPIBFlashes on GPIB activity.
RS232F las hes on RS 232 activity.
ERRORFlashes on an error in the execution of a remote or local
command including range error s .
10) Parameter Displ ayThe 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 LEDsThe 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 LEDsThese 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 ModuleThis 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 tThis 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 InputThe 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 ConnectorIf 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 ConnectorIf 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
IntroductionThe 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-OnWhen 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
OUTPUTSThe 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 50Ω 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 50Ω) 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 SELECTIONThe 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.
RampsRamp functions usually ramp up in voltage, downward ramps may be set
entering a negative amplit ude ( see AMPLITUDE section).
FREQUENCYTo 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.
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 FrequencyTo 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.
AMPLITUDEPress [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 50Ω). 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.
Output InversionThe 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. OnlyThe 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 OFFSETWhen 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 ENABLEPressing 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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