Voltage Control Ratiometric Readout Technique With Improved Dynamic Range and Power-Efficiency for Open-Loop MEMS Capacitive Accelerometer

MEMS capacitive accelerometer for the Internet of Things (IoT) applications is designed with open-loop structure rather than closed-loop structure to achieve low power consumption. In the open-loop structure, voltage control readout technique is preferred for low cost. However, the voltage control readout technique suffers from low dynamic range and low power efficiency (in terms of
$\mathbf {FoM}$
). In this paper, the voltage control ratiometric (VCR) readout technique is proposed to improve both dynamic range and power efficiency. The VCR readout technique is demonstrated in a readout circuit fabricated in a commercial 0.18
$\mu {\mathrm{ m}}$
1.8V/5.0V CMOS process. Compared to the traditional voltage readout circuit fabricated with the same CMOS process and tested with the same sensing element, the VCR readout circuit improves full input signal range by
$\mathbf {3.5dB}$
(from
$\boldsymbol {\pm 8g}$
to
$\boldsymbol {\pm 12g}$
) and the noise floor by
$\mathbf {9.5dB}$
(from
$\mathrm {\mathbf {804~\mu g/}}\sqrt {\mathbf {Hz}} $
to
$\mathbf {270~\mu g/}\sqrt {\mathbf {Hz}} $
). As a result, the dynamic range is improved by
$\mathbf {13.0dB}$
(from
$\mathbf {44.0dB}$
to
$\mathbf {57.0dB}$
), the
$\mathbf {Fo}\mathbf {M}_{\mathbf {1}}$
is improved from
$\mathbf {310pJ}$
to
$\mathrm {\mathbf {83pJ }}$
and the
$\mathbf {Fo}\mathbf {M}_{\mathbf {2}}$
is improved from
$\mathbf {1977~\mu W\cdot \mu g/Hz}$
to
$\mathbf {796~\mu W\cdot \mu g/Hz}$
.