Digital gate generation for a signal measurement instrument

Abstract

A method of digitally controlling the gate for a timing counter, to open and close the gate based on the occurrence of signal events, rather than on the envelope of the pulse. In a particular embodiment, a digital divider controls the gate, so that, when a pulse burst of RF is encountered, the gate opens on the second signal event. The divider can be programmed to close the gate any number of signal events later. Measurements are taken for an integral number of signal events, while counting time events from a precision clock. A series of measurements can be taken with various integral numbers of signal events for frequency profiling. By incrementing the digital divider from n to n+1 signal events for successive measurements, and subtracting the results, very narrow gates are effectively generated which move through the pulse cycle by cycle for frequency profiling. Because the opening of the gate is triggered by the IF events themselves, the gate is reliably and accurately positioned with respect to the pulse, and is unaffected by jitter in the pulse repetition interval.