An error model of phase discrimination based on spectral analysis is deduced to reduce the phase discrimination error for a phase-shift laser range finder, and the Hilbert transform is induced to data pre-processing to eliminate the estimation bias of phase difference. The bias and deviation of conventional spectrum analysis phase discrimination are analyzed. The analysis shows that the bias is influenced by initial phases and it can not be ignored in fast and precision measurement. This paper proposes an unbiased improvement method. The method uses a window function to design a simple Hilbert transformer to convert the objective of Discrete Fourier Transform into an analytic signal. Then the nearly unbiased phase difference measurement is achieved by spectral analysis only in increasing four addition and two shift operations. Simulation and experimental results indicate that the mean phase is the same as the real phase difference. When the signal to noise ratio is 40 dB, the measurement accuracy for the high speed phase discriminaton is 0. 1°. When the modulation frequency is 100MHz, the distance measurement accuracy is 0. 4 mm. Results show that the Hilbert transform can help spectral analysis realize high accuracy phase difference measuring and the method can be applied to fast phase-shift laser range finders.%针对相位式激光测距中的鉴相误差,建立了谱分析鉴相的误差模型,提出了在数据预处理中引入希尔伯特变换来消除相位差估计偏差的测量方法.分析了传统谱分析鉴相的偏差和方差,指出这些测量偏差受初相位的影响,在高速测距中不容忽略.提出了一种无偏改进方法,通过窗函数法设计正弦信号的简易希尔伯特变换器,将离散傅里叶变换的对象转换为解析信号,在仅增加4次加减法运算和2次移位操作的情况下,实现了近似无偏谱分析鉴相.仿真分析和实验验证结果表明,鉴相均值与真实相位差相同；当信噪比为40 dB时,每秒百万次高速鉴相的误差为0.1°；当调制频率为100 MHz时,测距精度达到0.4 mm.实验表明,将希尔伯特变换应用于谱分析鉴相,可实现高准确度相位差测量,并可应用于高速相位式激光测距.
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