Dither signal removal of ring laser gyro POS based on combined digital filter

Dither signal removal is the key foundation of high precision mechanically dithered Ring Laser Gyro (RLG) Position and Orientation System (POS). The present dither signal removal methods limited the gyro application in real-time measurement. The demands of RLG POS and the characteristics of linear phase FIR filter, low order IIR bandstop filter and IIR lowpass filter was Analyzed. A combined digital filter was adopted to remove dither signal. The combined digital filter consisted of a low order IIR bandstop filter, a low order IIR lowpass filter and a linear phase FIR lowpass filter. The low order IIR bandstop filter designed by Butterworth method can remove part of the dither signal which has the strongest power. With a low order Butterworth IIR lowpass filter, the combined filter can greatly reduce the high frequency noise. They both can reduce the order of FIR lowpass filter and the average group delay. To ensure high performance of the combined filter in low frequency bandwidth, designed a linear phase FIR lowpass filter. The experimental results show that a combined digital filter including a second order IIR bandstop filter, a 4th order IIR lowpass filter and a 42th order linear phase FIR lowpass filter can remove the dither signal effectively. Compared with an 89th order FIR filter, the computation complexity of the combined digital filter reduces by about 40%, and the group delay is decreased by about 40%. The combined digital filter reduces the hardware requirement of RLG POS and improves the real-time measurement performance.