| 摘要 |
Measurement of a time interval between a start and a stop event is made by activating a start oscillator in response to the start event and activating a stop oscillator in response to the stop event. The number of cycles of each respective oscillator signal which occur between the activation of each oscillator and the coincidence of the respective oscillator signal with that of an independent time base is determined. The number of cycles of the time base signal between the coincident points of it and the start and stop oscillator signal is also determined. These numbers, which are always integers, are used along with the values for the time base period and the difference in frequency between the time base oscillator and the start and stop oscillators to calculate the time interval. Resolution of the measurement is dependent on the frequency difference between the time base signal and the start and stop oscillator signals. Two triggered-phase oscillators, which are phase-locked to the reference oscillator, are used to supply the start and stop frequencies. The start trigger and stop signals are used for phase shifting, i.e., restarting of the oscillators rather than starting the oscillators. This allows for pre-trigger frequency control, and essentially eliminates post trigger frequency drift which usually occurs when an oscillator is first started. The coincidence signals are provided by the phase cross-over between the phase locked oscillator and the reference by a digital mixer.
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