中文说明：
假设输入被测信号为x=A*sin(w*n+θ)+u，其中A为幅值，θ为初相位，u为测量过程中的各种噪声。给出两个参考信号，r1=sin(w*n), r2=cos(w*n),与被测信号同频率。分别对x,r1和x,r2做互相关运算，A*sin(w*n+θ)这部分做互相关运算得到的值取w=0的部分可得到分别为A*cos(θ)/2和A*sin(θ)/2，由于噪声信号与正弦余弦信号不相关，故u这一部分输出为0。令a= A*cos(θ)/2，b= A*sin(θ)/2，故可得A=2√(a^2+b^2 ),θ=arctan(b/a)。
English Description：
Suppose the input measured signal is x = a * sin (w * n)+ θ)+ u. Where a is the amplitude, θ Is the initial phase, u is the various noises in the measurement process. Two reference signals, R1 = sin (w * n), R2 = cos (w * n), are given, which have the same frequency as the measured signal. The cross-correlation operation is performed on X, R1 and X, R2 respectively, a * sin (w * n)+ θ) In this part, the values obtained by cross-correlation operation are a * cos when w = 0（ θ)/ 2 and a * sin（ θ)/ 2. Because the noise signal is uncorrelated with sine cosine signal, the output of u is 0. Let a = a * cos（ θ)/ 2，b= A*sin( θ)/ 2, so a = 2 √ (a ^ 2 + B ^ 2), θ= arctan(b/a)。