One-Microsecond ADC Uses Gated, 55-Megacycle Oscillator

A dead-time of one-microsecond for 40 channels has been achieved with a Wilkinson type ADC. The nominal clock rate is 55 megacycles per second. The ADC consists of a linear-gate, a convertor section, a scaler, and three control monostables. The monostables establish an encode period when the conversion takes place, a transfer period when the word in the scaler is read in parallel, and a reset period when the scaler is reset. The scaler consists of six binaries connected in binary-coded-decimal (1-2-4-8-10-20). Another binary stores the overflow and another stores the anti-coincidence. The convertor uses a stretcher, a current generator, a comparator, and a unique 55-megacycle oscillator. The oscillator is gated both on and off with known and constant phase. The oscillator chosen inherently starts with known phase. The stop is accomplished by mixing the oscillator with the comparator output into a time delay circuit. The output of the time delay causes the stop. The stretcher will charge fully on a pulse of gaussian shape and 45 nanoseconds rise, foot-to-peak, and encoding will begin within 50 nanoseconds after the pulse peak. Operating characteristics, including independent linearity, differential linearity, and stability have been measured on a number of units.