Honors Thesis Archive

Author	Rebecca Cooper
Title	Achieving Nanosecond Timing with the Vernier Method
Department	Physics
Advisors	Elizabeth George, Paul Voytas, Adam Parker, and Dan Fleisch
Year	2009
Honors	Departmental Honors
Full Text	View Thesis (412 KB)
Abstract	Many subatomic processes occur in a small time frame, on the order of nanoseconds. We report on a project to create a circuit that can measure time intervals accurately on such a scale. To achieve this we used the Vernier Method, which is based on coincidence between two oscillators of slightly different frequencies. For accurate timing, the oscillators needed to have a stable, clean signal. The frequency needed to be in the MHz range, producing a pulse period of ~100 ns, and the pulse width needed to be narrow enough, on the order of a few nanoseconds, to produce only one coincidence. Relaxation oscillators based on unbuffered inverters in an RC circuit were used to generate square pulses at the required frequency. To shorten the pulses, we used a high-speed comparator circuit that created two pulses from the input pulse, one of which was inverted and delayed relative to the other, and an AND gate that combined the two, thus creating a shorter pulse. We have achieved a frequency of 4.5 MHz (a pulse period of 220 ns) and a width of 8 ns. Our circuit was tested by creating two input signals (a start signal and a stop signal delayed 150 ns by a 100 ft cable) with a Hewlett Packard 8082A pulse generator. Each signal triggered one of the oscillators to oscillate and the coincidence between them was observed. A flip-flop and counter can then be used to measure the time interval between start and stop.

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