Abstract
In recent years, with the progress of CMOS-MEMS technology, MEMS microphone gradually replaced the traditional Electret Condenser Microphone (ECM) and became the mainstream in consumer electronic products. Due to the small capacitance change single from MEMS microphone is quite small, a low noise readout circuit is needed to amplify the signal. Conventionally, the MOSFET with large size was used to reduce flicker noise, but it also caused the degradation of sensor signal. JFET has lower flicker noise than MOSFET so we designed a JFET as the input buffer for readout circuit to solve the problem and integrated the low noise amplifier with it. This IC was fabricated with TSMC 0.25μm BCD process. In order to verify the feasibility, we designed another circuit in which the JFET input buffer was replaced by a MOSFET as control group of samples. Confirmed by the measurement results, using JFET in the amplifier can reduce flicker noise, and compared to the MOSFET version obtain lower input referred noise.