Abstract : A simplified method is used to determine the limiting loop frequency limit of the phase-locked loop (PLL) and derive the general expression for the capture band. The simulation results obtained using this method on a typical control model are completely consistent with the results obtained by determining the capture band of the system using the traditional phase plane diagram method. This method is simple in procedure and intuitive in parameter adjustment, and has strong practical value in turntable performance testing. Keywords : capture band; phase-locked loop; test turntable; 1 Introduction A high-precision turntable low-speed servo system is composed of a phase-locked loop and an inductive synchronizer working together. The function of the turntable rate system is to enable the turntable to achieve various different speed motion states according to commands. However, for high-precision gyroscopes, if a control index of 0.0001 (°)/s rate resolution is required, it is difficult to achieve the requirements using conventional analog control schemes. However, by using digital phase-locked loop technology, based on the principle of digital pulse phase detection, the deviation signal is obtained through a phase difference-voltage conversion circuit (pump circuit), which can often achieve the required accuracy. The rate control employs a phase-locked loop (PLL) control method. Due to the rate difference between the output signal and the set signal, the phase detector in the PLL circuit detects this "beat frequency" and outputs a certain voltage signal. The rate PLL control system is a nonlinear control system; therefore, stability research is paramount to ensure its normal operation. The stability of the equilibrium state of a nonlinear system depends not only on the system's structure and parameters but also on the strength of external disturbances. Based on the magnitude of the disturbance that disrupts the equilibrium state, the stability problem of a nonlinear system can be divided into: stability problems under capture state and stability problems under synchronization state. [b][align=center]For more details, please click: Analysis of the Capture Band in a Turntable Rate System[/align][/b]