How to measure the frequency response of a waveform generator?

Question

I was looking at the data sheet of an arbitrary waveform generator and found a plot of the frequency response of the instrument, then wondered how it was measured. I know how to measure the frequency response of a simple electrical circuit. Basically I have an oscilloscope that can perform frequency response analysis, so I connect channel 1 to the input of the circuit and channel 2 to the output, then use a sweep sin wave over a range of frequencies, then the oscilloscope handles everything else and I get a bode plot of gain and phase. However, doing the same for the waveform generator will require taking apart the casing and some internal parts to get the circuitry, which may damage the device, let alone knowing where to connect the probes.

So does anyone have a suggestion how to measure it?

Answer 1

'Frequency Response' has to be understood in context.

For a circuit with an input and an output, it's as you say, the complex ratio of the output to the input signal versus frequency.

For a generator with only an output, it's ratio of the output power to the requested output power versus signal frequency.

To measure it, you'd connect it to an ideal receiver, and sweep its output frequency over its advertised range. The problem with this method is that you're measuring the response of both the generator and the receiver together.

If the receiver is an oscilloscope, you might hope that it's reasonably flat up to 50% or so of its advertised maximum frequency, as long as you are taking care to terminate any cables you use for connection.

For precision measurement of a source over frequency, we usually use a power meter, which has a far simpler construction than an oscilloscope or spectrum analyser, and is easier to make wideband.