A quick snapshot from our 20GS/S TDS7404. To build really high speed detectors and especially to built high speed amplifier/signal discriminators it is essential to have a reliable source of input test pulses. Standard TTL rise times are on the order of several nanoseconds. A factor of ten too slow (at least). when compared to the pulses coming out of advanced performance microchannel plate detectors.
We have tried the step recovery diode (SRD) but it only sharpens either the rising or falling edge. Is very picky about input amplitude and is incapable of producing a symmetrical pulse. The scope shot you see is from an Analog Devices ADCMP580 being driven by a SRS DG535. Pretty expensive solution to produce a test pulse! The DG535 will not reliably trigger the ADCMP580 for pulse widths less than about 2.1nS due to risetime limitations of the Stanford causing the output amplitude to drop precipitously. So that limits our minimum pulse width.
Because I need it, we are designing a pulse generator based on a very high speed CML output comparator. Line delays will be used to produce pulse widths of 60, 100, 500 and 1000pS. The output will be negative going so it is compatible with amplifier/discriminators designed for the output of microchannel based detectors. Analog output amplitude will be adjustable and there will be a Nim output as well. More specifications will be posted when the prototype is running.