考虑时间间隔测量对脉冲激光测距系统的意义,提出了一种新的高精度时间间隔测量方法。该方法在现场可编程门阵列(FPGA)中实现了脉冲计数法、多相采样法和延迟链法的结合。采用脉冲计数法对被测时间间隔进行“粗值”测量,保证大的动态测量范围。利用FPGA内部锁相环产生N路同频率,相位均匀分布的时钟信号作为计数时钟,基于等精度测频原理,将被测时间间隔的测时分辨率提高到Tclk/N。利用FlipFlop锁存器形成延时链,对被测信号与相邻计数时钟的时间间隔进一步量化。该方法解决了传统多相采样技术中由于倍频次数高导致相移分辨率降低的问题,在不增加计数时钟和有限延迟链数量的前提下,得到较高测时分辨率。测试结果表明,该时间间隔测量模块的动态测量范围为163.8 μs,测时过程相对较短,当进行多次重复测量时,测量的标准误差在71 ps以内,基本满足实际应用的精度要求。

The high accuracy time interval measurement is a key technique to a pulsed laser ranging. In this paper,a new high precision time interval measurement method combining with a pulse counting method,a multi-phase sampling and a delay method is proposed to use in the multi-level time interval measurement in a Field Programming Gate Array(FPGA). The pluse counting method is used to realize the coarse counter to guarantee a large dynamic range,and a Phase Locked Loop( PLL) in the FPGA is used to generate the N clock pulses with the same frequency and uniform distribution phase as counting clocks. Based on the equal precision frequency measuring,the resolution of the time conversion is improved to Tclk/N. Moreover,a latch Flip Flops is used to form a delay chain to measure the fine time interval. Experiments show that the proposed method has solved the problem of the traditional multi-phase sampling approach,to which phase shift resolution is decreased with the frequency increasing,so that the fine resolution can be obtained by limiting delay lines and no increase of counting clocks. The test results show that the maximum measuring time of the module is 163.8 μs,the conversion time is short and the standard error of the measurement is less than 71 ps when repeated measurements are carried out,which can satisfy the requirements of higher precision systems.