Analysis and design of a microphone preamplifier for mobile applications

Saemin Im, Sang Gyu Park

Research output: Contribution to journalArticlepeer-review


A design of an on-chip ac-coupling preamplifier for mobile applications is presented. A microphone preamplifier should have a large input impedance to mitigate the effective-gain reduction caused by the microphone’s non-zero output impedance. From a review of previously reported microphone preamplifier structures in terms of input impedance, feasibility of on-chip ac-coupling, and noise performance, we chose an inverting amplifier structure with capacitive feedback. In addition, to provide dc bias path, we used off-state MOSFET switches as pseudo-resistors of very large resistance in the giga-ohm range. The large resistance enables on-chip ac-coupling with sufficient noise performance. A fast start-up is achieved by turning-on the switch for a short period during the preamplifier start-up. The gain of the preamplifier can be programmed from 0 dB to 21 dB with 3 dB steps. A 2-stage pseudo-class-AB amplifier was adopted to reduce power consumption. The proposed preamplifier was implemented using a 28 nm CMOS process and achieves 107 dB dynamic range in a 20 kHz bandwidth under 0 dB gain setting and balanced differential input signal. The preamplifier dissipates a power of 270 µW with a 1.8 V supply.

Original languageEnglish
Article number1624
JournalElectronics (Switzerland)
Issue number14
StatePublished - 2021 Jul 2


  • Low-noise amplifier
  • Microphone preamplifier
  • On-chip ac-coupling
  • Programmable-gain amplifier


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