A VCO-Based ADC With Direct Connection to a Microphone MEMS, 80-dB Peak SNDR and 438-μW Power Consumption
- Resource Type
- Periodical
- Authors
- Perez, C.; Garvi, R.; Lopez, G.; Quintero, A.; Leger, F.; Amaral, P.; Wiesbauer, A.; Hernandez, L.
- Source
- IEEE Sensors Journal IEEE Sensors J. Sensors Journal, IEEE. 23(8):8466-8477 Apr, 2023
- Subject
- Signal Processing and Analysis
Communication, Networking and Broadcast Technologies
Components, Circuits, Devices and Systems
Robotics and Control Systems
Microphones
Micromechanical devices
Sigma-delta modulation
Modulation
Voltage-controlled oscillators
Power demand
Frequency conversion
Data conversion
micro electro mechanical systems (MEMSs)
microphone
sigma-delta modulation
voltage controlled oscillator (VCO)-ADC
- Language
- ISSN
- 1530-437X
1558-1748
2379-9153
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 $438 \mu \text{W}$ 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- $\mu \text{m}$ CMOS.