This paper presents a fully differential class-AB current mirror OTA that improves the common-mode behavior of a topology that presents very good differential-mode performance but poor common-mode rejection ratio (CMRR). The proposed solution requires a low-current auxiliary circuit driven by the input signal, to compensate the effect of the common-mode input component.
The low power instrumentation amplifier (IA) presented in this paper has been designed to be the front-end of an integrated neural recording system, in which common-mode rejection ratio (CMRR), input referred noise and power consumption are critical requirements. The proposed IA topology exploits a differential-difference amplifier (DDA) whose differential output current drives a fully differential, high-resistance, transimpedance stage, with an embedded common-mode feedback loop to increase the CMRR. This stage is followed by a differential-to-single-ended output amplifier.
A novel class AB operational transconductance amplifier (OTA) topology is proposed, based on a class AB flipped voltage follower. The OTA has class AB behavior, with current boosting both for the load and the compensation capacitors. It has a high gain of (gmr0)4, obtained using a two‐stage structure with cascoded stages, and is a two‐stage Miller‐compensated amplifier employing multipath to remove the positive zero.
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