A Differential Difference Amplifier with Preamplified Choppers for Electret/Condenser Microphones

• Main Authors: Hsuan-Yu Tsai, 蔡煊禹
• Other Authors: Hong-Chin Lin
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/02063637482679213538

碩士 === 國立中興大學 === 電機工程學系所 === 94 === This thesis proposes a differential difference amplifier with preamplified choppers for electret / condenser microphones. The most popular microphone preamplifier is source follower circuit. It can convert the impedance of microphone and extract the audio signals effectively. However, the single-ended amplifier’s noise rejection capability for common mode noise and power supply noise is not good enough, the linearity is also not quite well. Some papers propose the structure of differential difference amplifier to achieve high common mode rejection ratio (CMRR). However, the low frequency noise is still a problem to be overcome. Therefore, this thesis adds the theorem of the chopper stabilized amplifier by using the amplitude modulation skills to minimize the errors due to input offset and low frequency noise. Eventually, we combine the characteristics of source follower, differential difference amplifier, and chopper stabilized amplifier to generate a new powerful microphone preamplifier. The input impedance is larger than 100GΩ, with 21dB voltage gain, 115dB CMRR, and 64.8dB PSRR. Because the audio frequency range is 20Hz ~ 20kHz, the bandwidth is wider than 20kHz to meet the requirement. The new preamplifier has been simulated and fabricated using TSMC 0.35um CMOS 2P4M technology in area of 0.5mm² for 1.5V ~ 3V supply voltages and the power consumption is 463uW.