A VCO-based CMOS readout circuit for capacitive MEMS microphones Articles uri icon

authors

  • QUINTERO ALONSO, ANDRES
  • CARDES GARCIA, FERNANDO
  • PEREZ CRUZ, CARLOS ANDRES
  • BUFFA, CESARE
  • WIESBAUER, ANDREAS
  • HERNANDEZ CORPORALES, LUIS

publication date

  • January 2019

start page

  • 1

end page

  • 17

issue

  • 19

volume

  • 19

Electronic International Standard Serial Number (EISSN)

  • 1424-8220

abstract

  • Microelectromechanical systems (MEMS) microphone sensors have significantly improved in the past years, while the readout electronic is mainly implemented using switched-capacitor technology. The development of new battery powered “always-on” applications increasingly requires a low power consumption. In this paper, we show a new readout circuit approach which is based on a mostly digital Sigma Delta (ΣΔ) analog-to-digital converter (ADC). The operating principle of the readout circuit consists of coupling the MEMS sensor to an impedance converter that modulates the frequency of a stacked-ring oscillator—a new voltage-controlled oscillator (VCO) circuit featuring a good trade-off between phase noise and power consumption. The frequency coded signal is then sampled and converted into a noise-shaped digital sequence by a time-to-digital converter (TDC). A time-efficient design methodology has been used to optimize the sensitivity of the oscillator combined with the phase noise induced by 1/𝑓 and thermal noise. The circuit has been prototyped in a 130 nm CMOS process and directly bonded to a standard MEMS microphone. The proposed VCO-based analog-to-digital converter (VCO-ADC) has been characterized electrically and acoustically. The peak signal-to-noise and distortion ratio (SNDR) obtained from measurements is 77.9 dB-A and the dynamic range (DR) is 100 dB-A. The current consumption is 750 μA at 1.8 V and the effective area is 0.12 mm2. This new readout circuit may represent an enabling advance for low-cost digital MEMS microphones.

subjects

  • Electronics
  • Telecommunications

keywords

  • mems microphone; oscillator-based sensor; sigma-delta modulation; time-domain circuit; vco-adc