High Gain and High Bandwidth Fully Differential Difference Amplifier as Current Sense Amplifier

A current sense amplifier (CSA) based on a fully differential difference amplifier (FDDA) is introduced. A prototype was manufactured in a 0.18-μm bipolar, CMOS, DMOS (BCD) technology of Taiwan Semiconductor Manufacturing Company, Limited (TSMC) and characterized. The FDDA architecture offers several benefits regarding gain, bandwidth (BW), and noise performance and is well-suited for low-side phase-current measurement (PCM) in modern electric engines. To achieve a high gain accuracy, an integrated resistive feedback, which offers a low-frequency gain of more than 46 dB with a gain error of less than 1% and a 3-dB BW of approximately 2 MHz simulated and confirmed by measurements, is used. Hence, the circuit offers a higher measurement speed and sensitivity than the current state-of-the-art devices. Furthermore, the manual offset reduction allows for an input offset in the low microvolt range, and the input-referred noise is reduced to an input noise voltage of less than 30 μV (rms) and a noise floor of 13nV/√Hz (above 30 kHz). This article describes the design including the top-level structure, the distinct gain stages, the common-mode feedback (CMFB) and the output buffer amplifier of the CSA in detail. Finally, a measurement with a noisy rectangular 1-mV, 500-kHz signal proves the great potential of the amplifier for low-side PCM which is further compared with the state-of-the-art commercial products and research results.