Quadruply Split Cross-Driven Doubly Recycled <inline-formula> <tex-math notation="LaTeX">$g_{{m}}$</tex-math> </inline-formula>-Doubling Recycled Folded Cascode for Microsensor Instrumentation Amplifiers

Abstract

The requirement of high gain and low noise for sensor readout instrumentation is addressed in this brief. A novel current cross-mirroring technique is employed to enhance the small signal current of the proposed quadruply split cross-driven doubly recycled folded cascode (RFC) operational transconductance amplifier. The small signal current is increased by using split devices and two mirroring ratios (F and H), resulting in a double (or higher) transconductance $(g_{{m}})$ value and, hence, very high single-stage gain. Four fractionally split input differential pair transistors are utilized for achieving the further increase in gain without compromising the unity-gain–bandwidth (UGBW). Bias current splitting yielded a better slew rate and faster settling time. Results using the 130-nm IBM CMOS technology demonstrated a gain of 75 dB for the single-stage fully differential mode of the chopper-stabilized proposed enhanced- $g_{{m}}$ RFC. A significant open-loop UGBW of 166 MHz was also achieved in association with an 82.5° phase margin. In addition, an input-referred noise level as low as 48.3 $\mu\text{Vrms}$ was also achieved. A sensor readout circuit using the proposed instrumentation amplifier was verified using capacitive microsensors cofabricated on the 130-nm CMOS process, demonstrating wide dynamic range and high linearity.