This paper presents a direct conversion transceiver intended for use in a microfluidic NMR flowmeter. It consists of an H-bridge power amplifier, which drives a hand-wound milimeter-sized coil with RF signals, and a direct conversion receiver, which amplifies the NMR signals picked up by the coil, and then digitizes them with an asynchronous 8 bit SAR ADC sampling at 70 MHz. Fabricated in a 65 nm CMOS technology, the receiver achieves a noise spectral density of 1 nV/sqrt(Hz) at 21 MHz, while dissipating only 36 mW. A microfluidic flowmeter based on the transceiver and a handheld 0.5 T permanent magnet can measure flow rates up to 96 ml/h in a 0.8 mm inner-diameter channel with pm 1.3 % full-scale error. To the authors' best knowledge, this is the first reported portable NMR flowmeter.

This article presents a hybrid magnetic current sensor for contactless current measurement. Pick-up coils and Hall plates are employed to sense the high and low-frequency fields, respectively, generated by a current-carrying conductor. Due to the differentiating characteristic of the pick-up coils, a flat frequency response can then be obtained by summing the outputs of the coil and the Hall paths and passing the result through a 1st-order low-pass filter (LPF). For maximum resolution, the LPF corner frequency (2 kHz) is set such that the noise contribution of each path is equal. To suppress the coil-path offset without the use of large ac coupling capacitors, an area-efficient dual dc servo loop (D3SL) is used. This effectively suppresses the coil-path offset, resulting in a total offset of 73 μT , which is mainly dominated by the Hall path. Fabricated in a standard 0.18-μm CMOS process, the current sensor occupies 3.9 mm2 and draws 7.1 mA from a 1.8 V supply. It achieves 43 mA resolution in a 5 MHz bandwidth, which is 1.5 × better than the state-of-the-art hybrid sensors. It also achieves the lowest energy efficiency FoM (3.5 ×) among CMOS magnetic current sensors.

This article presents a hybrid magnetic current sensor for galvanically isolated measurements. It consists of a CMOS chip that senses the magnetic field generated by current flowing through a lead-frame-based current rail. Hall plates and coils are used to sense low-frequency (dc to 10 kHz) and high-frequency (10 kHz to 5 MHz) magnetic fields, respectively. With the help of on- chip calibration coils, the biasing current of the Hall plates is trimmed to match the sensitivity of the Hall and coil signal paths. The sensitivity drift of the coil path with temperature is compensated by using temperature-dependent gain-setting resistors, while the drift of the Hall path is compensated by biasing the Hall plates with a proportional- to-absolute-temperature (PTAT) current. The resulting sensitivity drift is less than 9% from-40 °C to 80 °C. The offset of the Hall plates is reduced by the current spinning technique, and the resulting ripple is suppressed by a multiplexed ripple-reduction loop (MMRL). Fabricated in a standard 0.18-μm CMOS process, the current sensor occupies 4.6 mm2 and draws 7.8 mA from a 1.8-V supply. It achieves a gain variation of only ±2% in a 5-MHz BW. It also achieves high energy efficiency, with an figure of merit (FoM) of 1.6 fW/Hz.

Magnetic current sensors are used in switched-mode power supplies and motor drivers, where both galvanic isolation and wide bandwidth (BW) are desired. In CMOS, Hall-effect sensors are widely used, but their resistance results in a fundamental trade-off between BW and resolution. Coils have a differentiating characteristic and so can achieve much wider BW and resolution, but cannot sense DC.