Optical Timing Receiver for the NASA Spaceborne Ranging System. Part I. Dual Peak-Sensing Timing Discriminator.

摘要

Position-resolution capabilities of the NASA Spaceborne Laser Ranging System are essentially determined by the time-resolution capabilities of its optical timing receiver. The optical timing receiver consists of a fast photoelectric device; (e.g.,photomultiplier or an avalanche photodiode detector), a timing discriminator, a high-precision event-timing digitizer,and a signal-processing system. The time-resolution capabilities of the receiver are determined by the photoelectron time spread of the photoelectric device,the time walk and resolution characteristics of the timing discriminator,and the resolution of the event-timing digitizer. It is thus necessary to evaluate available fast photoelectronic devices with respect to their time-resolution capabilities,to design a very low time walk timing discriminator and to develop a high-resolution event-timing digitizer which will be used in the high-resolution spaceborne laser ranging system receiver. The development of a new dual-peak sensing timing discriminator is described. The amplitude dependent time walk is less than +-150psec for a 100:1dynamic range of Gaussian-shaped input signals having pulse widths between 11and 17nsec. The unit produces 800mV negative output pulses,each 10nsec wide,and 3V positive pulses with widths of 15nsec. The time delay through the discriminator is approximately 37nsec. In this discriminator the input signal is processed by a peak-crossing circuit which produces a bipolar pulse having its zero-crossing point at the peak of the input signal. All essential functions in the discriminator are performed by means of tunnel diodes with backward diodes as nonlinear loads. The discriminator is designed to be CAMAC compatible to a conventional time-interval unit or a high-precision event timing digitizer. The adjustment procedure for obtaining minimum time walk is also given. (ERA citation 04:006480)