Nigel Goodwin said:
To get 1nS resolution you require a 1000MHz clock (1GHz), use the pulsed signal to gate the oscillator ON, just for the duration of the pulse. Feed the output of the gate into a chain of counters, and increment them with the 1GHz oscillator - after the pulse has finished the counters will contain the width of the pulse in nS.
I've been considering this very method, but hit a snag. The timing will be controlled by a microprocessor (running at 20Mhz for example) to start and stop the counter. If I use an external ECL counter running at a much higher speed, the net effect would be the same as using the mcu counter, multiplied difference in clock speeds eg x50 for a 1Ghz counter. The only effect that the external high-speed counter would have is effectively incrementing the counter by 20 instead of 1. The resolution will still be limited by the mcu in other words :? The same would be true of the linear ramp suggestion from Russlk, would it not?