If I use a short pulse from one generator to gate the output of another, the first being a pulse generator and the second being a function generator with a predfined output of N cycles of a sine at a given frequency and amplitude, I think that will generate what you mention. However, the specialized and precisely designed circuit to which you refer does one thing only, and very well, I'm sure, which will, generally speaking, exceed the quality of performance of the general purpose equipment I use. It takes about 15 minutes to set up my equipment, including measuring the trigger or gate pulse (whichever is needed for the function generator in question, measuring the frequency of the sinewave to the desired precision, and setting either a cycle count on a digitally controlled generator, or the appropriate gate width on an analog-controlled generator. Yours probably took considerably longer to design and fabricate, but, as a said, probably works much better, as it was designed for only one purpose.

I don't do this sort of thing often, but it's nice knowing that I can when I need to do so.

RE