Delay calibration for gamma camera timing circuit

Abstract

A method and apparatus for calibrating a programmable delay in a timing circuit of a gamma camera detector are provided. The programmable delay has an error, the value of which is to be determined. An input signal that is applied as input to the programmable delay is simultaneously applied as input to a precision fixed delay. The fixed delay has a delay value within the programmable range of the programmable delay, but has an error that is substantially smaller than that of the programmable delay. The output of the programmable delay is applied to one input of a decision circuit, and the output of the fixed delay is applied to another input of the decision circuit. The delay of the programmable delay is initially programmed to a value that is substantially greater than the delay of the fixed delay, and input pulses are then applied to both delays. The delay value of the programmable delay is progressively decreased as input pulses are applied, until the output of the decision circuit indicates that the outputs of both delays are asserted concurrently. The error of the programmable delay is then computed based upon the programmed delay value. The programmable delay is then reprogrammed with a new delay value, based on the computed error, to achieve a desired delay value during normal operation of the timing circuit.