A Fully Isolated Amplifier Based on Charge-Balanced SAR Converters

Abstract

A galvanic isolated amplifier based on SAR converters architecture is presented which realizes chip level isolation in both the power and signal domains. The compact IC package contains an integrated isolated power converter which includes on-chip transformer, oscillator and rectifier, digital isolators based on on-chip transformers, a front-end programmable gain amplifier, a SAR ADC, a complementary charge redistribution DAC, and post filters to reconstruct and smooth the linear signal. The symmetric implementation of the SAR ADC and DAC realizes the charge balance between the input side and the output side, where an inherent linear transfer function is achieved. The sampling clock comes from an on-chip oscillator of poor jitter performance which limits the SNR performance of the ADC. With the correlated clock for the DAC reconstruction, the close-in phase noise from the clock generator is attenuated so that the SNR performance of the overall isolated amplifier is not sensitive to the jitter from the sampling clock. This fully integrated solution displaces the traditional bulky hall-effect sensors, and enables precise and fast isolated voltage or current sensing applications such as photovoltaic inverters. The isolated amplifier, with the ability to measure both large currents and small dc injection currents in a single solution, can contribute compactly and efficiently to smart grid integration circuitry. The system-in-package achieves less than 1 mV total offset and 71.9 dBFS SNR in a bandwidth of 200 kHz. It achieves an isolation working voltage rating of 600 Vrms and 5 kVrms over 1 min duration.