Function / Signal Generator
Test Instrument
Produces known test signals — sine, square, triangle, pulse, arbitrary waveforms — so you can feed a circuit a clean stimulus and watch what it does. The scope's natural partner: one talks, the other listens.
What it looks like
Function / Signal Generator
A typical test instrument — exact shape, colour and markings vary between manufacturers.
Types & variants
Key specs
Frequency range
µHz – MHzBench DDS units: 0.01 Hz to 25–60 MHz sine (square usually tops out lower).
Waveforms
—Sine, square (variable duty), triangle/ramp, pulse, noise, DC offset, and arbitrary point-by-point shapes on AWGs.
Amplitude & offset
VppTypically 1 mVpp–20 Vpp into open circuit with ±10 V DC offset. NOTE: into 50 Ω the displayed amplitude halves — the classic gotcha.
Output impedance
Ω50 Ω source. Set the generator's load menu (50 Ω vs High-Z) to match reality or amplitudes read wrong.
Modulation & sweep
—AM/FM/PM, frequency sweep (for filter response plots), burst mode (N cycles per trigger).
Markings
BNC main output(s), sync/trigger output, channel enable buttons. Two-channel units allow phase-locked pairs (great for differential or quadrature tests).
Standard values
Hobby favourites: FY6900/JDS6600 dual-channel DDS (₹5–8k class), UNI-T/OWON bench units, XR2206 solder kits for learning. Pro: Siglent SDG series AWGs.
How to choose
1) Frequency ceiling ≥ your fastest test (audio work needs only 1 MHz; MCU filter work 25 MHz+). 2) Two channels for stereo/differential/mixer testing. 3) Clean square-wave edges matter for digital testing — check rise time spec. 4) Sweep + scope = poor-man's Bode plotter for filters and amplifiers. 5) Protect the output stage: never connect it to a powered/driven node.
Pinout & package
50 Ω BNC outputs, sync out, external trigger/counter input. Kits: PCB with BNC or screw terminals. MCU route: DAC/PWM pins with RC filtering for improvised signals.
Example circuits
- Sweeping 20 Hz–20 kHz through an amplifier while the scope watches for clipping and rolloff
- 1 kHz square wave into an RC network to visualise the time constant
- Injecting a signal at a radio's IF to trace where a dead receiver loses it
- Burst mode pinging an ultrasonic transducer pair
Common failures
Blown output stage from connecting into live circuits or shorts at high amplitude, amplitude errors from the 50 Ω/High-Z setting mismatch, distorted output above rated frequency, and noisy encoders on cheap units.
How to test
Loop into the scope: verify amplitude (mind the load setting), frequency against the scope's counter, and waveform purity. Sine distortion audible/visible at low amplitude signals output-stage damage.
Substitutes
An MCU PWM pin + RC filter makes serviceable test tones; a PC sound card generates <20 kHz audio-band signals; a 555 astable is the classic improvised square-wave source. For RF, cheap ADF4351/Si5351 boards generate carriers.