Some experiments with a tiny part that has remarkable qualities: the Analog Devices ADCMP580. It is a comparator, and a very fast one indeed, based on a SiGe semiconductor.
Its features are true extraordinary – everything specified in GHz and picoseconds.
Well, can this be made work without a lot of money invested in a special HF or microwave board? Yes, it can. You just have to keep the wires short:
This test board was constructed by first soldering thin wires to the chip, and then mounting it on a small piece of perf board, with some epoxy glue. The output is wires, within less than 2 mm, to a (50 Ohm) SMA connector.
Measuring the performance characteristics is not an easy task. I used a 54750a sampling scope, with a 54751a 20 GHz bandwidth plug-in.
The comparator is fed by a 8642b signal generator, which is also used to trigger the 54751a plug-in.
At the output, a 13.5 dB attenuator is used, at least for some of the tests, to get best output SWR (to avoid issues caused by reflected signals). However, as it turns out, the 54751a has quite reasonable input SWR, and the connecters are better than it first seemed. So the attenuator can be left out. Still good to have some attenuators at the 54751a input, remember, this can only handle +-2 V, and no ESD!
In these tests, “squaring up” a 500 MHz and 2 GHz (!) signal. Rise and fall time are about 50 ps, not bad at all for the simple construction.
FFT shows bandwith to 10 GHz and up.
Output power is also quite useful, 400 mV Vpp.