Design and comparison of the application of EPLL and QPLL in a digitalized gyroscope system

Abstract

To optimize conventional phase locked loop (PLL) performance through enhancement of drive mode stability of frequency and amplitude, enhanced phase locked loop (EPLL) and quadrature phase locked loop (QPLL) algorithms were investigated. First, stable point averaging analysis was applied to verify the stability of the closed-loop and determine the range of the critical parameters. When simulations were conducted to compare PLL, EPLL and QPLL, it was found the use of QPLL resulted in superior control precision and noise suppression. Next, different nonlinear dynamic closed-loops in PLL modules allowed for stable amplitude and constant frequency in the drive mode, and parameter estimates were needed for both EPLL and QPLL algorithms without amplitude demodulation. Then, after the control parameters were optimized, the EPLL and QPLL algorithms were compared at the module level by Field Programmable Gate Array (FPGA) chip, and specified amplitude and frequency startup characteristics were analyzed. Finally, under the same test conditions, system level experiments were implemented to compare some major specifications of the digital gyroscope system. During experiments, the phase noise of the drive mode detection signal was utilized to estimate the frequency control stability. The QPLL based gyroscope yielded better bias instability with 4.34°/h and a noise floor of 0.0229 °·s−1/Hz, while the EPLL system was only 9.33°/hwith a noise floor of 0.0711°·s−1/Hz.