| Summary: | The proposed delta-sigma modulator (△ΣM) based signal acquisition architecture uses a differential difference amplifier (DDA) customized for dual purpose roles, namely as instrumentation amplifier and as integrator of △ΣM. The DDA also provides balanced high input impedance for signal from sensors. Further, programmable input amplification is obtained by
adjustment of △ΣM feedback voltage. Implementation of other functionalities, such as filtering and digitization have also been incorporated. At circuit level, a difference of transconductance of DDA input pairs has been proposed to reduce the effect of input resistor thermal noise of
front-end R-C integrator of the △ΣM. Besides, chopping has been used for minimizing effect of Flicker noise. The resulting architecture is an aggregation of functions of entire signal acquisition system within the single block of △ΣM, and is useful for a multitude of dc-to-medium frequency sensing and similar applications that require high precision at reduced size and power. An implementation of this in 0.18-μm CMOS process has been presented, yielding a simulated peak signal-to-noise ratio of 80 dB and dynamic range of 109 dBFS in an input signal band of 1 kHz while consuming 100 μW of power; with the measured signal-to-noise ratio being lower by
about 9 dB.
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