Signal generator (function and arbitrary waveform generator)

01

Check frequency by waveform, sample rate and memory

RIGOL's DG900 Pro data sheet lists, for the DG902/912/922 Pro, sine to 70, 150 and 200 MHz, but square only to 60 MHz, pulse to 50 MHz, ramp to 3–5 MHz and arbitrary waveforms to 30–50 MHz, with a 1.25 GSa/s sample rate, 16-bit vertical resolution and 16 Mpts per channel (32 Mpts optional) of waveform memory. Output modes include continuous, modulation (AM, FM, PM, SUM, ASK, FSK, PSK, PWM), sweep and burst, and the generator also offers noise, harmonic and pulse functions. [2]

Editorial calculation: at 1.25 GSa/s a 200 MHz sine has 1.25 × 10⁹ / 200 × 10⁶ = 6.25 samples per cycle, and the same data sheet lists arbitrary waveforms only to 30–50 MHz; compare generators on the frequency of the waveform you will actually use. [2]

Editorial note: list the waveforms, modulation and sweep types, channel count and memory depth your tests need before comparing models.

Give the supplier the waveforms and maximum frequencies, amplitude and offset ranges, load impedance, number of channels and channel coupling, arbitrary waveform length, modulation and sweep needs, external clock or trigger, interfaces and software, and calibration certificate requirements.

02

Check amplitude into your load, accuracy and signal quality

The DG900 Pro lists amplitude ranges of 1 mVpp–10 Vpp into 50 Ω up to 50 MHz, falling to 1 mVpp–2 Vpp at 200 MHz, and 2 mVpp–20 Vpp into high impedance up to 50 MHz; amplitude accuracy of ±(1% of setting + 2 mVpp) into 50 Ω; output impedance of 50 Ω ± 1%; frequency accuracy of ±10⁻⁶ of setting and a ±2 ppm time base from 0 to 40 °C; and outputs that switch off automatically on overload. [2]

For signal quality it gives harmonic distortion of below −55 dBc from 10 Hz to 10 MHz (−50 dBc to 50 MHz, −40 dBc above), total harmonic distortion below 0.1% from 10 Hz to 20 kHz at 1 Vpp, non-harmonic spurious below −65 dBc to 10 MHz, and phase noise below −110 dBc/Hz at 10 kHz offset for a 20 MHz sine; RIGOL's product page cites rise times as low as 3 ns and a 60 MHz square wave with fast rising edges. [1]

Editorial calculation: because the range doubles from 1–10 Vpp into 50 Ω to 2–20 Vpp into high impedance, a generator set for 1 Vpp assuming a 50 Ω load will deliver about 2 Vpp into a high-impedance input; set the generator's load setting to match the circuit. [2]

03

Compare what suppliers offer

Suppliers linked to this page list function or arbitrary signal generators; each card links to the page reviewed.

The suppliers reviewed list bench and handheld signal generators; ask each for maximum frequency per waveform, sample rate and resolution, memory, amplitude range into 50 Ω and high impedance, accuracy, distortion and jitter specifications, and calibration.

04

Check distortion, flatness and burst limits at your top frequency

Tektronix's AFG31000 datasheet shows how sine quality changes across the band of one generator. For the AFG31151/31152/31251/31252 it gives typical harmonic distortion at 1 Vpp of < −72 dBc from 10 Hz to < 1 MHz but < −37 dBc from 25 MHz to 250 MHz, and amplitude flatness (1 Vpp, relative to 1 kHz) of ±0.2 dB below 5 MHz widening to ±1.0 dB from 100 to 200 MHz and ±2.0 dB from 200 to 250 MHz. In burst mode the sine limit is half the continuous one: 1 μHz to 125 MHz on the 250 MHz models and 1 μHz to 12.5 MHz on the 25 MHz models. [3]

For the output it lists 50 Ω output impedance, a selectable load impedance setting (50 Ω, 1 Ω to 10.0 kΩ, or High Z) that adjusts the displayed amplitude, 42 Vpk maximum isolation to earth ground, and relays that disconnect the outputs when incoming current exceeds 250 mA. Frequency accuracy is ±10⁻⁶ of setting from 0 °C to 50 °C, with aging of ±1.0 × 10⁻⁶ per year. [3] Editorial note: ask each supplier for distortion and flatness at the highest frequency you will use, burst-mode limits, and output protection, not only the headline sine bandwidth.

05

Check triangle, pulse and arbitrary limits, not only sine range

Rohde & Schwarz's product page for its R&S HMF2525 and HMF2550 arbitrary function generators gives frequency ranges of 10 μHz to 25 MHz and 10 μHz to 50 MHz, but triangle waveforms only up to 10 MHz and pulses with a recurrence rate up to 12.5 MHz or 25 MHz by model. It lists 5 mV to 10 V (Vpp) into 50 Ω and an arbitrary waveform generator of 250 Msample/s, 14 bit and 256 kpoint. Pulse width can be set from 15 ns to 999 s with 5 ns resolution, and rise and fall time selected from 8 ns to 500 ns. [4]

Editorial calculation: on the 50 MHz model the 25 MHz pulse limit is half the sine limit and the 10 MHz triangle limit one fifth of it (50 ÷ 25 = 2; 50 ÷ 10 = 5). Its 8 ns minimum edge compares with rise times as low as 3 ns on RIGOL's product page. [4] [1]

Editorial note: list the waveform, frequency, edge time and arbitrary record length each test needs, and ask suppliers for the limit of each.

06

Trace the generator functions

This is a functional reference built from the sources cited; it is not one maker's design.

07

Fill the specification fields with values for your tests

A signal generator quotation needs values for your tests. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

08

Send the waveform, load and quality data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Waveforms: [types; max frequency each]
Amplitude: [range; offset; load impedance]
Quality: [distortion; jitter; rise time]
Channels: [number; coupling]
Arbitrary: [length; sample rate]
Functions: [modulation; sweep; burst; trigger]
Calibration: [certificate; interval]

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