A time interval counter permits the time interval between a first signal and one of a series of timing signals to be measured to less than .+-.2 nanoseconds without using microwaves and high power-consuming devices. The time interval counter uses a first passive delay time operated from the first signal, which occurs at an unknown interval from the timing signals, to produce a plurality of binary outputs spaced from each other by known equal time intervals that are substantially less than the interval between the timing signals, and a second passive delay line operated by the timing signal, which occurs after the first signal, to produce a plurality of sequential outputs spaced from each other by a plurality of known sub-time intervals that are substantially less than the time interval between the plurality of binary outputs of the first delay line. The time interval counter also includes means to store the plurality of binary outputs of the first delay line at each of the sub-time intervals produced by the second delay line, and means to determine the time interval between the first signal and timing signal from the stored binary outputs of the first delay line by interpreting the earliest stored binary outputs and the stored binary outputs at each sub-time interval and combining the interpretation and comparison to calculate the time interval.
An adaptive time period measurement technique which provides full speed for every measurement period with increased resolution afforded from repeated measurements. The time measure is produced by adaptively filtering a number of prior time measures. Each measurement includes a count and a fractional part from a controlled variable delay interposed in the measurement system. This variable delay is controlled over a number of measurements to cover the entire range of one clock cycle, preferably in accordance with a reversed binary progression algorithm. The adaptive filtering is preferably a self-modifying, classic low pass filter with a roll off which depends on the rate of change and direction of change of the measurerd time period. Thus the present invention provides all the resolution feasible based upon the rate of change of the measured quantity.
