Design of a High Precision Time Interval Measurement Circuit

Aiming at the problems of low precision, low resolution and small range of time interval measurement, a high precision and high resolution time interval measurement circuit was designed. Through the combinational logic circuit and sequential logic circuit composed of six D triggers, the time interval t to be measured was split into large time interval t₁₂, which was larger than the clock period, and small time interval t₁ and t₂, which were smaller than the clock period. Driven by the external clock, FPGA used the direct counting method to directly obtain the count value Q by the internal counter, and multiplied the Q and the clock cycle to get t₁₂. Based on time-amplitude conversion method, the t₁ and t₂ were made as the open and close signal of high-speed switch to control capacitor discharge time, and then the time measurement was converted into analog voltage measurement. Capacitance voltage before and after discharge was obtained by using a 16-bit high resolution ADC, and high resolution t₁ and t₂ were obtained by combining the capacitance voltage and capacitance discharge formula of constant current source. The measured t₁, t₂ and t₁₂ were transferred to the upper computer, and the time interval t was obtained by calculating. The results of theoretical analysis and experimental measurement show that, the circuit time interval measurement range can reach 10~6 s, the resolution is optimized to 1.5 ps, and the measurement accuracy can reach 10 ps.