Applications such as rangefinders and ballistic chronographs require a high resolution measurement of time. This can be a time period of a few hundred nanoseconds to a few milliseconds. This is an analog circuit that can convert a time period to a voltage with high linearity and high resolution. In principle, a current source is used to charge a capacitor for the time interval and then the voltage across that capacitor is measured. A REF200 precision current source is used to furnish 200uA to a fast SPDT analog switch, represented by SW1 & SW2. This switch steers the current into ground or into a 100pF capacitor C2. U1 is simply a high- precision buffer amplifier for the voltage on C2. SW3 is a reset that zeros the voltage on C2. Initially, SW3 is open and SW2 steers the 200uA to ground until a START command is received; SW2 then opens and SW1 closes, steering the current into C2. The capacitor charges until a STOP command is received; SW1 then opens and SW2 closes. The voltage on C2 is proportional to the time between START and STOP; scale time range is determined by the value of C2 so this capacitor should be high quality. A polystyrene or NPO (COG) ceramic is recommended for C2. A small DMOS SD211 can be used for SW3. (Circuit is created by Neil P. Albaugh, TI-Tucson)
Time-to-Voltage Converter circuit:
Online Simulation of a Time-to-Voltage Converter circuit:
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