Design Examples

A Chopper Current-Feedback Instrumentation Amplifier With a 1 mHz <formula formulatype="inline"><tex Notation="TeX">$1/f$</tex> </formula> Noise Corner and an AC-Coupled Ripple Reduction Loop

“…Their difference is then nulled by the gain of . The overall feedback ensures that the output currents of and cancel and thus the amplifier's gain is given by (1) For bridge readout, a CFIA is more suitable than a traditional instrumentation amplifier because the CFIA uses both current-source isolation and nulling techniques to achieve a high CMRR [13]. Secondly, it can easily handle independent input and output common-mode voltages.…”

“…Restrictions apply. The DC loop gain corresponding to the ripple reduction ratio is given by (13) The phase shift within the loop mainly originates from three blocks: integrator and , a differentiator and an integrator . In this design, pF, pF, kHz, is about 114 dB, so the dominant pole is at around 0.8 mHz.…”

“…A class-AB output stage was implemented to achieve rail-to-rail output. To save power, the class-AB mesh structures were incorporated into the output branch of the intermediate stage [13]. The class-AB mesh was also cascoded to reduce the variation of the drain-source voltages of .…”

“…Due to the CT nature of the loop, this approach does not suffer from noise folding. By using a three stage nested-Miller topology [13], and chopping the input and intermediate stages, the amplifier achieves a noise corner of 1 mHz at a noise density of 15 nV/ Hz.…”