Used Function Generators for Sale

A function generator produces standard periodic waveforms — sine, square, triangle, ramp, and pulse — at frequencies from a few hertz to 20 or 80 MHz depending on the model. It is the right tool for driving a circuit under test with a known periodic stimulus. A signal generator (RF signal generator) produces CW and modulated signals in the RF and microwave range (typically 100 kHz to 40 GHz) and is optimized for receiver testing and RF measurements. An arbitrary waveform generator (AWG) can produce any user-defined waveform stored as a digital sequence — capturing a real signal, editing it, and replaying it through the output. Many modern function generators include AWG capability, making the distinction less sharp at the low end.

For general-purpose lab work — circuit debugging, filter testing, sensor drive, transducer excitation — a 20 MHz function generator covers the vast majority of applications. The Agilent 33220A (20 MHz) and HP 33120A (15 MHz) are the workhorses of this class. For pulse and digital timing applications where you need fast rise times and square wave fidelity, a higher-frequency unit like the Agilent 33250A (80 MHz) is preferred because the squareness of the output improves with higher instrument bandwidth. For audio and low-frequency sensor work, even a 1 MHz instrument is sufficient.

Arbitrary waveform output lets you define a custom waveform as a sequence of voltage samples stored in the instrument memory, then output it repeatedly at a specified sample rate. You use AWG capability when you need to simulate a non-standard signal shape — a cardiac waveform for medical device testing, a distorted power line waveform for immunity testing, an amplitude-keyed pulse train, or a specific sensor output pattern. The Agilent 33220A has a 64,000-sample arbitrary waveform memory and 200 MSa/s sample rate. The HP 33120A has a 16,000-sample memory at 40 MSa/s.

Single channel is sufficient for most general-purpose lab work — driving a circuit input, providing a reference signal, or testing a single-port component. Dual channel output (like the Keysight 33500B or Tektronix AFG3022B) is needed when you require two phase-related signals simultaneously — I and Q drive for a quadrature modulator, differential drive for a balanced amplifier, or two synchronized signals with a controlled phase relationship for delay and phase testing. Dual-channel instruments also allow summing two waveforms at the output for AM modulation without an external mixer.

Most function generators have a 50 ohm source impedance with a switchable output termination setting. When driving a 50 ohm coaxial load (most RF and microwave applications), set the output impedance to 50 ohms — the displayed amplitude is the voltage at the 50 ohm load. When driving a high-impedance load (oscilloscope input, CMOS gate, op-amp input), set the output impedance to Hi-Z — the instrument doubles the output voltage to compensate for the unterminated transmission line, so the displayed amplitude is the open-circuit voltage. Using the wrong impedance setting causes the actual output to differ from the displayed value by a factor of 2.

Annual NIST-traceable calibration is standard for instruments in quality system environments. Function generator calibration covers output frequency accuracy, output amplitude accuracy across the full frequency and level range, DC offset accuracy, symmetry, and duty cycle where applicable. Frequency accuracy on a crystal-referenced synthesizer is very stable — an Agilent 33220A calibrated two years ago likely still meets the 1 ppm frequency specification if stored at room temperature. Amplitude calibration drifts more, typically 0.5 to 1% over two years. We calibrate to Agilent and HP published specifications and issue certificates with measured data.

The HP 33120A and Agilent 33220A have excellent reliability records. The most common failure mode is output connector wear — the BNC output connector degrades after thousands of cable insertions, causing intermittent contact. On the HP 33120A, the output amplifier can fail if the output has been sustained into a short circuit. Display and keypad failures are common on units from the early 2000s from membrane switch wear. On the Agilent 33250A, the DDS chip and high-speed DAC are the critical components — failures are rare but expensive to repair. All of these issues are bench-diagnosable with a repair estimate before committing to work.

Burst mode outputs a specified number of waveform cycles in response to a trigger, then stops and waits for the next trigger. It is used in applications where you want to generate a finite packet of cycles rather than a continuous waveform — pulsed ultrasound transducer drive, gated measurement windows, trigger-synchronized test stimuli for digital systems, and network impulse response testing. The Agilent 33220A supports triggered burst, gated burst, and internally triggered burst. Burst count is settable from 1 to 50,000 cycles, with phase start angle control so each burst begins at the same phase point.