Nanopower OTAs with improved linearity and low input offset using bulk degeneration

In this paper, a study of bulk degeneration in a differential pair to enhance its linear range is initially conducted. A nanopower operational transconductance amplifier (OTA) is then proposed combining both source and bulk degeneration to achieve an increased linear range above 1 V with a power supply ranging from 1.9 V to 5.5 V. The circuit was fabricated in a 0.6 μm technology and measured. This linearity improvement is achieved with a negligible increase in power consumption, noise, and input referred offset. Finally a circuit implementing the full signal conditioning of a piezoelectric accelerometer for adaptive pacemakers is presented, as an application example of the proposed OTA. The circuit consumes only 500 nA, and it can discriminate signals of 15 μV, because of the low input referred offset < 5 mV of the source-bulk linearized OTA.