Stanford Research Systems DS345 Data Sheet

· 1 µµHz to 30.2 MHz frequency range

· 1 µµHz frequency resolution

· Sine, square, ramp, triangle & noise

· Phase-continuous frequency sweeps

· AM, FM, burst and phase modulation

· 16,300 point arbitrary waveforms

· 10 MHz reference input

· RS-232 and GPIB interfaces (opt.)

· DS345 ... $1595

(U.S. list)

Stanford Research Systems phone: [phone]

www.thinkSRS.com

The DS345 is a full-featured 30 MHz synthesized function
generator that uses an innovative Direct Digital Synthesis
(DDS) architecture. It generates many standard waveforms
with excellent frequency resolution (1 µHz), and has versatile
modulation capabilities including AM, FM, Burst, PM and
frequency sweeps. It also generates arbitrary waveforms with
a fast 40 Msample/s update rate.

Functions and Outputs

The DS345 generates sine waves and square waves at
frequencies up to 30.2 MHz, and triangle and ramp waveforms
up to 100 kHz. The frequency resolution for all functions is
1 µHz. In addition to the standard waveforms, the unit also
provides a wideband (10 MHz) white noise source.

Both the function output and a TTL SYNC output are
available through floating, front-panel BNC connectors. Both
outputs have 50 Ω output impedances and may be floated up
to ±40 V relative to earth ground. The amplitude of all
function outputs is adjustable from 10 mVpp to 10 Vpp with
3-digit resolution, and can be displayed in Vp, Vpp, Vrms or
dBm. In addition, standard TTL and ECL output levels can
be selected.

Additional useful connectors are provided on the rear panel. A
trigger input is used to trigger arbitrary waveforms,
modulation patterns, sweeps and bursts, while a TTL trigger
output is provided to allow synchronization of external

DS345 Function/Arb Generator

Synthesized Function Generators

DS345  30 MHz function and arbitrary waveform generator

www.thinkSRS.com

devices to sweeps and bursts. A sweep output generates a
0 to 10 V ramp synchronous with frequency sweeps. The
sweep marker outputs allow specified portions of a frequency
sweep to be highlighted on an oscilloscope.

A 10 MHz rear-panel input allows the DS345 to be
synchronized to an external timebase. A 10 MHz rear-panel
output allows multiple DS345s to be phase locked together.

Modulation

The DS345 offers a wide variety of modulation options. It
contains an internal modulation generator which can modulate
any of its standard waveforms except noise. The modulation
waveform can be a sine, square, triangle, ramp, or an
arbitrary waveform. Modulation rates from 1 mHz to 10 kHz
can be selected.

The modulation generator can provide amplitude modulation
(AM), frequency modulation (FM), and phase modulation
(PM). When using AM, modulation depths of ±100 % can be
selected with 1 % resolution. Negative values of modulation
correspond to Double Sideband Suppressed Carrier (DSBSC)
modulation. FM spans can be selected with 1 µHz resolution,
and phase modulation can be set between 0° and 7200° with

0.001° resolution.

External Amplitude Modulation

In addition to the internal modulation generator, the output
waveform can be amplitude modulated by an external signal
applied to the rear-panel AM input. This input is always
activeeven when other modulation types are turned on.

DS345 Function/Arbitrary Waveform Generator

Stanford Research Systems phone: [phone]

www.thinkSRS.com

Frequency modulation

Phase modulation

Amplitude modulation

Square, triangle and ramp waveforms

Burst Modulation

You can generate tone bursts of any output function except
noise. In the burst mode, the DS345 will output an exact
number of complete waveform cycles after receiving a trigger.
By adjusting the phase, you can control where in the
waveform the burst begins. While using the burst mode, the
maximum frequency for sine waves and square waves is
1 MHz, while triangles and ramps are limited to 100 kHz. Burst
mode may be used with arbitrary waveforms at any frequency.

Frequency Sweeps

The DS345 can frequency sweep any of its function outputs
(except noise). You can sweep up or down in frequency using
linear or log sweeps. Unlike conventional function generators,
there are no annoying discontinuities or band-switching
artifacts when sweeping through certain frequencies. The
DS345's DDS architecture inherently allows it to perform
smooth, phase-continuous sweeps over it's entire frequency range.

Two sweep marker frequencies can be specified. When the
sweep crosses either of the marker frequencies, a TTL
transition is generated at the rear-panel MARKER output to
allow synchronization of external devices.

Arbitrary Waveform Capability

The DS345 isn't just a function generator. It's also a full­featured arbitrary waveform generator. Output waveforms
have 12-bit vertical resolution, and can be played back at rates
up to 40 Msamples/s.

Since composing complex arbitrary waveforms at the
keyboard can be a tedious task, Arbitrary Waveform
Composer (AWC) software is provided at no charge. AWC is
a menu-based program which lets you create and edit arbitrary
waveforms on the screen, store them, and download them to
the DS345.

DS345 Function/Arbitrary Waveform Generator

Stanford Research Systems phone: [phone]

www.thinkSRS.com

Frequency sweep

Arbitrary waveform

Burst modulation

AWC software

Frequency Range

Max. 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/N (sample

rate)

Output

Source impedance 50 Ω
Grounding Output may float up to ±40 V

(AC + DC) relative to earth ground.

Amplitude

Range 0.01 to 10 Vpp (50 Ω),

20 Vpp (Hi-Z)
Resolution 3 digits (DC offset: 0 V)
Sine wave accuracy (0 VDC offset)

5 to 10 Vpp ±0.2 dB (1 µHz to 20 MHz)

±0.3 dB (20 MHz to 30.2 MHz)

0.01 to 5 Vpp ±0.4 dB (1 µHz to 20 MHz)

±0.5 dB (20 MHz to 30.2 MHz)
Square wave accuracy

5 to 10 Vpp ±3 % (1 µHz to 100 kHz)

±6 % (100 kHz to 20 MHz)

±15 % (20 MHz to 30.2 MHz)

0.01 to 5 Vpp ±5 % (1 µHz to 100 kHz)

±8 % (100 kHz to 20 MHz)

±18 % (20 MHz to 30.2 MHz)
Triangle, ramp and ±3 % (>5 Vpp)

arbitrary accuracy ±5 % (<5 Vpp)

DC Offset

Range ±5 V (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

Sine Wave

Spurious components < −55 dBc (non-harmonic)
Phase noise < −50 dBc in a 30 kHz band

centered on the carrier, exclusive of

discrete spurious signals
Sub-harmonic < −50 dBc

DS345 Specifications

Stanford Research Systems phone: [phone]

www.thinkSRS.com

Harmonic distortion Level Frequency Range

< −55 dBc DC to 100 kHz
< −45 dBc 0.1 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 + 4 ns
Overshoot <5 % of peak to peak amplitude at

full output

Ramps, Triangle and Arbitrary Waveforms

Rise/fall time 45 ns (10 MHz Bessel filter)
Linearity ±0.5 % of full-scale output
Settling time <1 µs to settle within 0.1 % of final

value at full output

Arbitrary Waveforms

Sample rate 40 MHz/N, N = 1 to 2

34

−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),

15 kHz max. (external)
Distortion < −35 dB at 1 kHz, 80 % depth
DSB carrier < −35 dB (typ.) at 1 kHz modulation

rate (DSBSC)
External input ±5 V for 100 % modulation,

100 kΩ impedance, 15 kHz BW

Frequency Modulation

Source Internal (sine, square, triangle, ramp

or arbitrary)
Rate 0.001 Hz to 10 kHz
Span 1 µHz to 30.2 MHz (100 kHz for

triangle, 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 0.001 s to 1000 s
Span 1 µHz to 30.2 MHz (to 100 kHz for

triangle, ramp)

Markers Two markers may be set at any

sweep point (TTL output)

Sweep output 0 to 10 V linear ramp signal,

synchronized to sweep

Burst Modulation

Waveform Any waveform except noise may be

burst modulated.

Frequency Sine and square to 1 MHz

Triangle and ramp to 100 kHz
Arbitrary to 40 MHz sample rate

Count 1 to 30,000 cycles/burst (1 µs to

500 s burst time limits)

Trigger Generator

Source Single, Internal, External, Line
Rate (internal) 0.001 Hz to 10 kHz

(2-digit resolution)
External trigger Positive or negative edge, TTL
Output TTL level

Standard Timebase

Accuracy ±5 ppm (20 °C to 30 °C)
Aging 5 ppm/year
Input 10 MHz/N ± 2 ppm (N = 1 to 8),

1 Vpp minimum input level
Output 10 MHz, >1 Vpp sine into 50 Ω

Optional Timebase

Type Ovenized AT-cut oscillator
Stability <0.01 ppm, 20 °C to 60 °C
Aging <0.001 ppm/day
Allan variance (1 s) <5 × 10

−11

DS345 Specifications

Stanford Research Systems phone: [phone]

www.thinkSRS.com

General

Interfaces Optional RS-232 (300 to 19.2 kbaud,

DCE) and GPIB with DOS based
arbitrary waveform software (AWC).
All instrument functions are controllable
over the interfaces.

Non-volatile memory Nine sets of instrument settings can

be saved and recalled.

Dimensions 8.5" × 3.5" × 13" (WHD)
Weight 10 lbs.
Power 50 W, 100/120/220/240 VAC,

50/60 Hz

Warranty One year parts and labor on defects

in materials and workmanship

Ordering Information

DS345 30 MHz function/arb. generator $1595
Option 01 GPIB, RS-232 and arb. software $495
Option 02 10 ppb OCXO timebase $650
O345RMD Double rack mount kit $85
O345RMS Single rack mount kit $85

DS345 rear panel (with opt. 01)

Direct digital synthesis (DDS) has had a dramatic impact on
the best approach to bench-top function generators. Over the
last few years, improvements in LSI logic, fast random access
memories (RAM), and digital-to-analog converters (DACs)
have made DDS the technology of choice for this application.

There are three major components to DDS: a phase
accumulator, a sine look-up table, and a DAC. The phase
accumulator computes an address for the sine table (which is
stored in RAM). The sine value is converted to an analog
value by the DAC. To generate a fixed-frequency sine wave, a
constant value (called the Phase Increment) is added to the
phase accumulator with each clock. If the phase increment is
large, the phase accumulator will step quickly through the sine
look-up table, and so generate a high-frequency sine wave.

One might think that to generate a clean sine wave you would
need hundreds or thousands of points in each cycle of the sine
wave. In fact, you need about three. Of course, a three step
approximation to a sine wave hardly looks like a sine wave,
but if you follow the DAC with a very good low-pass filter, all
the high-frequency components are removed, leaving a very
clean sine wave.

The frequency resolution of the DDS is given by the number
of bits in the phase increment and phase accumulator.

DS345 Function/Arbitrary Waveform Generator

Stanford Research Systems phone: [phone]

www.thinkSRS.com

manybits provide very high frequency resolution. The DS345
uses a 48-bit phase accumulator for a frequency resolution
of one part in 10

14

. This provides 1 µHz resolution at all

frequencies from 1 µHz to 30 MHz.

The maximum frequency depends on how fast you can add the
48-bit phase increment to the phase accumulator. Using a
highly pipe-lined architecture, these additions can be
performed at 40 MHz. This allows direct digital synthesis to
15 MHz. A frequency doubler is used to reach 30 MHz.

For agile frequency and phase modulation, it is necessary to
change the phase increment values quickly. To do this, the
phase accumulator may switch between two 48-bit phase
increment values in 25 ns, and each of these 48-bit registers
may be loaded in less than 1 µs. During frequency modulation
one register is used while loading the other.

What is Direct Digital Synthesis (DDS)?

DDS block diagram

40MHz Clock

AM Input

Modulation RAM

DDS345 ASIC

Amplitude DAC

Waveform

RAM

Amplitude

Control

12 bit

DAC

Square Wave
Comparator

Output

Amp

Cauer Filter x2

10 MHz Bessel Filter

Sync

Output

Function

Output

Attenuators