Generate Square Wave with Fast Rise Time for Testing

Question

I'm looking to economically generate a 1-2 GHz (configurable) Square Wave with a rise time of 200ps (or faster) to test the performance of various active scope probe designs. I don't need to be able to alter things such as duty cycle or power, however it would be ideal if the output was at least -10 dBm (71 mV RMS) across the frequency range. No modulation is needed beyond a simple periodic square wave.

Does anyone know of some economical off-the shelf equipment or evaluation board which would meet this need?

Answer 1

Typical approach is to build a multivibrator with standard logic, and just use really fast logic to get the desired edge rate. Bus drivers can be used for higher output into a transmission line (while abusing ratings less), or multiple gates can be connected in parallel, at some compromise in performance (the propagation delays won't be perfectly matched, smearing out the edge slightly).

Here are examples from another community:
Yet another fast edge pulse generator - Leo Bodnar | EEVblog Forum
Compact 74AC14 pulse generator PCB - rfmerrill | EEVblog Forum
W2AEW #88: Cheap and simple TDR using an oscilloscope and 74AC14 Schmitt Trigger Inverter | YouTube

ECL/CML/LVDS gates are effective for fast rates at low voltages, and CMOS gates e.g. 74AC, LVC, AUC, etc. are effective at higher voltages and somewhat slower edge rates (fractional ns).

Answer 2

The technology to produce this is called Current Mode Logic or CML formerly called ECL.

You don’t need a frequency to test an active prove or GHz DSO, just the 10~90% risetime to measure 0.35/Tr = f-3dB

Then apply FFT on the result for spurious ripple.

Here is a novel avalanche stripline picosecond pulser:
Designed by the late Jim Williams who started when I did in Analog electronics in the ‘60’s.

http://www.siliconvalleygarage.com/projects/picosecond-pulser.html