In this paper, we present a broadband (5-780MHz) transceiver ASIC optimized for$^{ \boldsymbol {1}}\text{H}$and X-nuclei nuclear magnetic resonance (NMR) with external custom-designed microcoils. The NMR-on-a-chip transceiver is realized in a 0.13$\mu \text{m}$BiCMOS technology, consumes an area of$1100 \boldsymbol {\times }900\mu \text{m}\,\,\boldsymbol {^{2}}$, and integrates a quadrature receiver, consisting of a low-noise amplifier, a quadrature downconversion mixer, and intermediate-frequency variable gain amplifiers, a power amplifier, and a frequency synthesizer on a single chip. An extensive noise analysis of the BJT-based low-noise amplifier with regard to the optimum source impedance provides simplified expressions for an optimized LNA design for broadband NMR-on-a-chip applications. The NMR-on-chip transceiver provides a measured state-of-the-art input-referred voltage noise of 610pV/$\sqrt {\text {Hz}}$and a maximum RX gain of 66dB. In combination with an external, custom-designed solenoidal microcoil, the presented NMR-on-a-chip transceiver achieves a state-of-the-art normalized$^{ \boldsymbol {1}}\text{H}$spin sensitivity of$7.2 \boldsymbol {\times } 10^{ \boldsymbol {17}}$spins$/\sqrt {\text {Hz}}\cdot \text {T}^{ \boldsymbol {2}}/\text{m}$with an untuned, i.e. broadband front-end. Proof of concept NMR experiments on multiple nuclei ($^{ \boldsymbol {1}}\text{H}$,$^{ \boldsymbol {2}}\text{H}$,$^{ \boldsymbol {13}}\text{C}$, and$^{ \boldsymbol {19}}\text{F}$) verify the applicability of the proposed untuned, broadband approach.

In this paper, we present an integrator-differentiator transimpedance amplifier (I-D-TIA) with a dc compensation, which incorporates widely tunable multi-element pseudo-resistors (MEPRs) in its dc servo loop and ac signal path. The implemented MEPR in the dc path is continuously tunable from$460 \,\mathrm {k\Omega }$to$300 \,\mathrm {G\Omega }$allowing the TIA to process dc currents with a dynamic range of more than$100 \,\mathrm {dB}$. The MEPR in the differentiator ac signal path provides a tunable resistance between$0.3 \,\mathrm {M\Omega }$and$100 \,\mathrm {M\Omega }$, resulting in an overall ac transimpedance between$3 \,\mathrm {M\Omega }$and$1 \,\mathrm {G\Omega }$. For the lowest ac transimpedance, a bandwidth of$10 \,\mathrm {MHz}$is achieved. The TIA provides a minimum input-referred current noise density of$1.6\,\mathrm {fA}/\mathrm {\sqrt {Hz}}$. The implemented MEPR has been optimized regarding its high-frequency noise by minimizing its parasitic capacitances. The MEPR shows an inherent shot noise suppression such that its noise stays close to the theoretical thermal noise limit and significantly below the theoretical shot noise limit, even for large dc currents. By using a sub-VSS supply for the MEPR, the asymmetry in its output characteristic is greatly reduced, leading to a linear signal swing of$1.5\,\mathrm {V_{pp}}$with a THD below$1 \mathrm {\%}$on a$1.8-\mathrm {V}$supply. Thanks to this high linearity, large bandwidth, and high dc current dynamic range, the proposed TIA can be used in a wide variety of applications from high-sensitivity, low-bandwidth lock-in detection to transient current sensing with sub-microsecond timing resolutions.