A new method to determine the period in sigma delta modulator with DC input

Sigma delta modulator was used as A/D converter in many applications. By calculating 1-bit data stream directly in a period has high resolution with short time. According to the periodic characters of the output bit string in sigma delta modulator with DC rational input, a new method based on the correlation analysis was given to fix the period of output bit string. Assuming the output 1-bit data stream in a sigma delta modulator is y(n), considering the output series y(n) of finite length, its autocorrelation function ryy(0) (when m=0) is maximum. Calculating autocorrelation function ryy(m)continuously until m=T, when ryy(T)= ryy(0), T is the cycle period. By averaging y(n) in T interval can obtain corresponding input level value. Any DC input signals can be regard as a rational based on the system precision, the period T was obtained from the modulator output and is independent of the initial condition, so the method has important significance in practical application.