The Folded Ramp: A New Technique for Computer-Controlled Time-Interval Measurement

This paper describes the folded-ramp circuit, a computer-controlled device for measurements of time intervals from a few nanoseconds to a few seconds. The features of this circuit are single-range operation, binary-output format, measurement-error detection, and an output-register capacity that is set by dynamic range rather than accuracy or resolution. The circuit generates a ramp-type waveform that reverses slope at approximately 0 V and at a predetermined peak voltage; control of the ramp slope makes each leg of the folded ramp 100 ns in duration. The measured time interval is described by the number of slope reversals plus the amplitude difference between the voltage at termination of the measurement and at the last reversal. The circuit allows measurements of time over a 109 to 1 range with accuracies better than 1 percent of reading ±0.5 ns.