A <inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math> </inline-formula>NMR CMOS Transceiver Using a Butterfly-Coil Input for Integration With a Digital Microfluidic Device Inside a Portable Magnet

Abstract

This paper describes a 20 MHz micro-nuclear magnetic resonance ( $\mu $ NMR) transceiver (TRX) featuring a butterfly-coil input for chemical/biological assays. It enables integration with a 2D multi-electrode digital microfluidic (DMF) device inside a space-limited portable magnet (0.46 T, 1.25 kg), making multi-sample management compatible with $\mu $ NMR measurements, and supporting electronic automation. The transmitter (TX) incorporates a pulse-sequence synthesizer followed by an inverter-based power amplifier (PA), to emit the exciting pulses for magnetizing the protons of the samples. For the receiver (RX), it is headed by a multi-stage low-noise amplifier (LNA) using NMOS-PMOS-complementary differential pairs, achieving a sub-nV/ $\surd $ Hz input-referred noise at low power. Sixth-order Butterworth low-pass filters constitute the core of the RX I/Q baseband. Their source-follower-based topology allows fast and coherent scaling of all poles by the bias current, reducing the dead-time of the RX for better sensitivity. Fabricated in $0.18~\mu \text {m}$ CMOS, the TRX occupies a die area of 2.1 mm2, consumes 6.6/23.7 mW of power in the TX/RX mode, and demonstrates the feasibility of electronic-automated biological (avidin) and chemical (CuSO4) assays achieving a detection limit on avidin of 0.2 pmol.