Design And Implementation Of Digital Signal Processor For Resonant Micro Optic Gyro

An optic gyro is a kind of the high-precision inertial angular rotation sensor based on the Sagnac effect. It’s widely used in the navigation and inertial guidance systems. Compared with a fiber optic gyro, a resonant micro optic gyro (RMOG) with a waveguide-type ring resonator (WRR) has the irreplaceable advantages for miniaturization and integration. The double closed-loop RMOG is better than the single closed-loop RMOG for the reduction of reciprocal noises, the enhancement of gyro bandwidth and the improvement of the nonlinearity. The digital signal processor for the single closed-loop RMOG is improved and optimized and a digital processor for the double closed-loop RMOG is designed and firstly constructed on a single field-programmable gate array (FPGA). This digital processor not only has the performance of low-noise, low-delay, high-reliability and high-configurability, but also is beneficial for the integration of the RMOG.A low-noise, low-delay digital signal processor for the RMOG is designed by theoretical analysis and simulation. And the sinusoidal phase modulation and loop feedback technology are adopted in this processor. The direct digital frequency synthesizer (DDS) which can meet the frequency resolution and avoid additional phase noise is chosen as the driver for the acoustic optic frequency shifter (AOFS). Furthermore, the gyro signals are easy to be read out by using DDS.A digital signal processor for the double closed-loop RMOG is constructed on an FPGA. This processor consists of a sinusoidal modulation signals generator, a demodulation module, a proportional integrator (PI) module, a DDS timing controller and a gyro signal extraction module. The equivalent input noise of this processor is as low as5.53nV/VHz which can detect an equivalent Sagnac effect of30°/h in an RMOG with a2.5-cm diameter resonator. The processing delay of the first closed-loop and the second closed-loop are1.1μs and1.6μs respectively which are greatly improved compared to300μs implemented by instruments. This improvement is so crucial as to achieve a high loop gain and lower the reciprocal noises. The frequency resolution of the DDS is0.116Hz which is equivalent to the resonance frequency difference generated by the gyro rotation of2.15°/h.Based on the work above, the digital processor is used in the double closed-loop RMOG. The locking precision of the first closed-loop and the second closed-loop are0.0039°/s and0.0055°/s respectively over an hour and the long bias stability is0.502°/s with the integration time of1s. Moreover, the gyro can clearly distinguish the sinusoidal oscillation with the frequency of0.1Hz and the peak of°0.1°/s and the scale factor nonlinearity of the gyro system is reduced from0.448%to0.131%.