基于ALTPLL的水声测量用相位计设计

Phase meter used in under-water measurement based on ALTPLL

以ALTERA公司的FPGA为核心,设计了一种水声测量用高精度的相位计。相位差的测量基于过零鉴相法,即利用过零比较器将2路同频正弦信号整成脉冲信号,然后通过测量两路脉冲信号的周期和上升沿之间的时间差来测量相位差。本文特色在于2路脉冲信号上升沿之间的时间差测量利用了ALTERA公司FPGA中集成的锁相环模块ALTPLL,该模块可以输出多路具有固定相位偏移的系统时钟信号,时间差测量时实际使用的时基信号为其中上升沿最接近待测信号上升沿和下降沿的2路系统时钟信号,从而降低了计数法测量时间间隔的±1误差。实验结果表明利用该方法可以将水声测量领域的相位差测量不确定度降低到0.1度。

A high-accuracy phase meter used in under-water measurement based on FPGA is designed.The measurement of phase difference is based on zero crossing comparator and phase detector,where two channel sine wave signals of the same frequency are shaped to pulse signals,then the period and the time interval of rising edge of the two channel pulse signals are measured to calculate the phase difference.In the process of measurement,ALTPLL module in FPGA manufactured by ALTERA corporation is used to measure the time interval of rising edge of two channel pulse signals.The ALTPLL module can generate multi-channel coherent clock signals and two of the clock signals whose rising edge is mostly near the rising edge and falling edge of the signal to be tested are used as the time-base signals,so the ±1 error in time interval measurement is reduced.Experiment results show that using ALTPLL module can reduce the phase difference measurement uncertainty in under-water measurement to 0.1 degree.