A Multi-Hit Drift Time Digitizer

We describe electronics for a drift chamber which measures drift times and has multi-hit capability. The system is based on a stable (± 0.005%) 125 MHz clock which eliminates the need for frequent calibrations. The times are digitized according to a Gray code in order to restrict transition errors to the least significant bit. The least count is 4 ns which contributes an rms error of 58 μm to the measurement of drift distance.