A low noise capacitance to voltage readout circuit based on active feedback charge sensitive amplifier for micro-gyro

Area of Science:

• Electrical Engineering
• Microelectromechanical Systems (MEMS)

Background:

• Capacitance-voltage (C-V) readout circuits are crucial for micro-machined gyroscopes.
• Trans-impedance amplifier (TIA) based circuits suffer from thermal noise due to high-value feedback resistors.

Purpose of the Study:

• To analyze and compare the noise performance of TIA and charge sensitive amplifier (CSA) based C-V readout circuits.
• To design and evaluate a novel CSA-based C-V readout circuit for micro-gyroscopes.

Main Methods:

• Theoretical analysis and simulation of TIA and CSA noise performance.
• Design and fabrication of a CSA-based C-V readout circuit using 180 nm CMOS technology.
• Experimental testing of C-V gain, output noise, and resolution.

Main Results:

• Thermal noise of feedback resistors in TIA circuits dominates output noise.
• The designed CSA circuit achieves a C-V gain of 225 dB and output noise below 150 nV/Hz.
• The fabricated chip demonstrates a resolution of 840 zF/Hz at 1 V bias voltage.

Conclusions:

• CSA-based C-V readout circuits overcome the noise limitations of TIA circuits.
• The designed CSA circuit offers significant advantages in noise performance and area, making it suitable for micro-gyroscope integration.