An all-electronic, I/Q-mixer-based interferometric technique to reduce measurement noise in the characterization of extreme impedances is presented. The proposed technique employs a standard vector network analyzer, an arbitrary waveform generator and an I/Q-mixer chain to generate a very stable cancellation signal. This hardware implementation enables frequency scalability, due to the large commercial availability of the mentioned components, and high stability, speed and repeatability, due to the fully electronic approach. The proposed technique is embedded in a scanning microwave microscopy (SMM) setup to demonstrate a more than 50% noise reduction in the measurement of dielectric materials.

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Abstract-A compact sensing pixel for the determination of the localized complex permittivity at microwave frequencies is proposed. Implemented in 40-nm CMOS, the architecture comprises a square patch, interfaced to the material-under-test (MUT) sample, that provides permittivity-dependent admittance. The patch admittance is read out by embedding the patch in a double-balanced, RF-driven Wheatstone bridge. The bridge is cascaded by a linear, low-IF switching downconversion mixer, and is driven by a square wave that allows simultaneous characterization of multiple harmonics, thus increasing measurement speed and extending the frequency range of operation. In order to allow complex permittivity measurement, a calibration procedure has been developed for the sensor. Measurement results of liquids show good agreement with theoretical values and the measured relative permittivity resolution is better than 0.3 over a 0.1-10 GHz range. The proposed implementation features a measurement speed of 1 ms and occupies an active area of 0.15×0.3 mm 2 , allowing for future compact arrays of multiple sensors that facilitate 2-D dielectric imaging based on permittivity contrast.