A CMOS MAGFET-Based Programmable Isolation Amplifier

Abstract

In this paper, we present a high common mode voltage amplifier with a novel isolation technique. In this proposed structure, a minimum of 430 V isolation is satisfied from on-chip intermetal SiO2 layers. On the high-voltage side, an adjustable gain amplifier that supports ±2.5 V of differential voltage drives the coil. However, on the low-voltage side, a CMOS integrated magnetic field sensitive MOSFET (MAGFET) placed under the coil converts the generated magnetic field into a current imbalance which will be transformed to a differential voltage via a cascode stage. In addition, based on the ADC input dynamic range, the signal amplitude is adjusted by using a 6-bit dB-linear programmable gain amplifier (PGA) with a gain range of 0 to 54 dB and a maximum gain-nonlinearity error of 0.2 dB. This PGA has a temperature independent characteristic with a maximum gain error of 0.21 dB over a temperature variation between −40 to 80 °C. The design achieves a low input offset of 0.18 mV. It has also a low current consumption of 1.2 and 2.3 mA for the high voltage and the low voltage side, respectively.