Time interval measurements using time-to-voltage conversion with built-in dual-slope A/D conversion

An integrated CMOS circuit for measuring a time interval given as the width of a pulse is presented. The circuit converts the time interval to be measured to a longer interval which can be digitized more accurately using a clock than the initial one. The circuit is a combination of a time-to-voltage converter (TVC) and a dual-slope A/D converter. In the time-to-voltage conversion a capacitor is discharged with a constant current during the time interval to be measured. The use of dual-slope A/D conversion reduces the effects of current and capacitance value drifting due to temperature changes. The measurement range (50-500 ns) can be scaled with the discharging current (12-90 μA). The resolution of the time-to-voltage conversion is 200 ps or better. The A/D conversion uses a 10 MHz clock for digitization, giving an overall resolution of 400 ps