Test And Analyse Of The Interface Ciecuit For The Capacitance Micro-Gyroscope

Nowadays, high-performance interface circuits of the micro-gyroscope adapt closed-loop driving method to achieve better sensibility and reliability. The total system does not need external driving signal to drive the micro-gyroscope. The driving signal is produced by the interface circuit itself. However, researches on the micro-gyroscope limit on the fabric domestic and are far behind advanced level.This paper mainly tests the interface circuit of the micro-gyroscope, and therefore, based on the results of the test, defects of the interface circuit are analyzed. First of all, the theory and principle of the micro-gyroscope is studied. On the base of that, the equivalent electrical analogue of gyroscope is produced. Through simulation of the electrical analogue, the relationship of the driving signal, the displacement in the drive direction and the sense current of the drive part is concluded. In order to validate the feasibility of the total closed-loop driving circuit of the micro-gyroscope, the phase transformation and the gain of the system is demonstrated in theory. Therefore, the phase transformation from the sense current of the drive part to the driving signal is 180°. However, the driving force is square of the driving signal. Therefore, the phase transformation of the total is zero ensuring the micro-gyroscope can be vibrated in the view of phase. The closed-loop interface circuit has greater gain ensuring the micro-gyroscope can be vibrated in the view of gain. Therefore, the micro-gyroscope can be vibrated at its natural frequency.After discussing the feasibility of the total closed-loop driving circuit, each of the devices in the closed-loop interface circuit is tested, including the charge amplifier, the phase-transformation device, the pulse wave modulator and the driving signal. During the process of the test, some defect in the closed-loop driving circuit is found which is mainly brought by the charge amplifier. The charge amplifier has phase error which changes with the work frequency of the micro-gyroscope which can cause the micro-gyroscope may not be vibrated.In order to eliminate the phase error of the interface circuit, the transimpedance amplifier is used to substitute the charge amplifier. In order to achieve high gain of the transimpedance amplifier, the feedback resistor must be very big. However, big diffused resistors in the integrated circuit occupy lots of area and have great noise. Therefore, active resistor is used to substitute the passive resistor as the feedback resistor of the transimpedance amplifier.Through simulation, the natural frequency of the micro-gyroscope is 2.7kHz. The driving force is in phase with the sense current of the drive part. The phase error is 9°at the natural frequency of the micro-gyroscope. Through test of charge amplifier, phase compensation device, square-wave generator and driving circuits, the micro-gyroscope can vibrate at its natural frequency.