Function generator
The bench box: sine, square, triangle or sawtooth, with the knobs on the front and a real 50 ohm output.
This is the instrument version of the signal generator. Two differences, and both of them matter. It has a sawtooth, which is the ramp a sweep is made of and which nothing else in the catalog produces. And its output is not ideal: it drives through 50 ohms, which is what the connector on the front of a real one is terminated for, so a load pulls the amplitude down by exactly the divider between 50 ohms and that load.
Pins
| Pin | What it does |
|---|---|
OUT |
The waveform, behind 50 ohms. |
GND |
The reference the waveform is measured against. |
Properties
wave: sine, square, triangle or sawtooth. frequency: in hertz, 1000 by default.
amplitude: the peak swing either side of offset, 2.5 by default. offset: 2.5
by default, so the stock settings give a 0 V to 5 V swing. duty: the square wave's
duty cycle, 50 by default.
The shape, the frequency and the amplitude also have buttons on the face, stepping 1, 2, 5 per decade the way a real dial is marked, so a circuit can be swept by hand without opening a panel. Offset and duty are panel-only.
What the model gets right
The waveform goes into the analog solver rather than being stepped by the part, so the solver puts a breakpoint on every square-wave edge and every sawtooth fly-back and lands exactly on it instead of integrating through it. The 50 ohms is a real element in the matrix, not a correction applied afterwards: into 50 ohms you measure half the amplitude you asked for, into 1 k about 95% of it, into a megohm all of it.
What it does not model
No distortion, no amplitude or frequency drift, no sweep mode. A sweep here is pressing the frequency button, which is a step rather than a glide. No modulation and no burst.
The waveform is mathematically exact: a square wave's edges are vertical with no rise time, a sine has no harmonics, and there is no noise floor, no jitter and no DC offset error. The 50 ohms is a pure resistance with no reactance and no frequency dependence. There is no output protection or current limit (the generator will drive a short circuit forever) and no upper frequency limit other than what the solver's own step can follow, so asking for a megahertz gives a megahertz rather than the rolled-off, distorted thing a real box would produce.
Common mistakes
Wondering where half the signal went. Into a low-impedance load the 50 ohms is a voltage divider, and a real bench generator does this too; the figure is printed beside the output posts. If you want an ideal source with no output impedance, the plain signal generator is the part for that.
See it in action
RC filter on the bench drives a low pass from this part and reads both ends of it on the oscilloscope, with a multimeter on the output. Open it at /templates, and see the bench instruments for how the three work together.