Reconfigurable Closed-Loop Digital ΔΣ Capacitive MEMS Accelerometer for Wide Dynamic Range, High Linearity Applications
Keywords:
Noise transfer function, electronic filter, feedback, MEMS sensorAbstract
Closed-loop capacitive MEMS accelerometer is
similar to a ΔΣ ADC where the MEMS sensor introduces
second-order dynamics in the loop. The sensor has limited
signal gain, hence provides very limited noise shaping capability
to other noise contributions within the loop. Furthermore,
fabrication non-idealities can cause unwanted stability issues in
higher order closed-loop operation. We present a 4th order ΔΣ
closed-loop system with a digital 2nd order ΔΣ modulator. The
digital ΔΣ modulator allows fine accuracy in choosing the
coefficients for the ΔΣ modulators. It also provides flexibility in
the placement of poles and zeros for compensating the
unforeseen phase delays caused by fabrication non-idealities.
Our system is able to achieve an SNR > 120dB in simulation
and > 90dB from experiment with an evaluation board. The
digital implementation of ΔΣ modulator allows us to build
reconfigurable closed-loop system with the potential for even
higher order system which can be optimized to suit different
MEMS sensor characteristics and performance.
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