Development of Multistage Digital Filters for Dither Signal Removal in Ring Laser Gyro

Ring Laser Gyroscopes (RLG) are widely used in Inertial Navigational Systems for detection of body rotation. But the performance is limited by lock- in state of RLG. To avoid this problem the Laser cavity of RLG is mechanically dithered. This process ensures that RLG stays out of the lock- in zone during its operating condition. But the dither signal appears as noise, which must be removed to obtain the true rotation of the body. This can be achieved by the use of digital filters. The required digital filter should have very high attenuation in the dither band and linear phase response in the pass band. Two types of multistage digital filters namely BBB and BCO filters are developed to remove the dither signal to an acceptable level. The BCO combined filter is found to be good and the same filter is implemented in real time using FPGA. The simulated results and the real time results are compared and found to be nearly same in both cases.