A VCO-Based ADC With Direct Connection to a Microphone MEMS, 80-dB Peak SNDR and 438-muW Power Consumption Articles uri icon

publication date

  • February 2023

start page

  • 8466

end page

  • 8477


  • 8


  • 23

International Standard Serial Number (ISSN)

  • 1530-437X

Electronic International Standard Serial Number (EISSN)

  • 1558-1748


  • This article presents a microphone readout chip incorporating a voltage controlled oscillator (VCO)-based ADC that can be directly connected to a capacitive micro electro mechanical systems (MEMSs) sensor without requiring a voltage buffer. The ADC uses an open-loop pseudo-differential architecture with two ring oscillators followed by a coarse-fine frequency-to-digital converter. The proposed coarse-fine architecture optimizes power consumption, thanks to a new algorithm. The MEMS is connected to the ring oscillators with a source follower circuit that can be programed to interchange signal to noise ratio (SNR) by the power consumption in small steps. This feature enables always-on operation in voice recognition applications. The microphone is compatible with standard PDM audio interfaces. Total ADC power consumption ranges between 245 and 438-μW for peak signal-to-noise and distortion ratios (SNDRs) between 74 and 80.3 dB-A, including the ADC and MEMS coupling circuitry. The dynamic range (DR) achieves 108 dB at full performance with a total harmonic distortion (THD) of 1.5% at the acoustic overload point (AOP) of 128 dBSPL. The ADC occupies an area of 0.14 mm2 implemented in 0.13-μm CMOS.


  • Electronics


  • microphones; micromechanical devices; sigma-delta modulation; modulation; voltage-controlled oscillators; power demand; frequency conversion