A Broadband Sensor Interface IC for Miniaturized Dielectric Spectroscopy From MHz to GHz Mehran Bakhshiani, Student Member , IEEE , Michael A. Suster , Member , IEEE,a n d

Abstract

This paper describes a broadband sensor interface IC as part of a miniaturized measurement platform for MHz-t o-GHz dielectric spectroscopy. Developed in 0.35 µm 2P/4M RF CMOS, the IC measures frequ ency-dependent S 21 magnitude and phase of am i c r ofluidic dielectric sensor fabricated in a thick gold-on-glass microfabrication process and loaded with a material-under-test (MUT). The IC architecture implements a broadband frequency response analysis (bFRA) method by first down -converting the sensor response signal from th e RF excitation frequency to an intermediate frequency (IF) o f 1 MHz using a low-noise ampli fier (LNA) and active mixer, followed by down-converting the IF signal to dc using a coherent detector employing IF ampli fication stages with programmable gain, a passi ve mixer driven by in-phase (I) and quadrature-phase (Q) signals anda na c t i v e - R Cl o w - p a s sfilter (LPF). The sensor interfaced wit h the IC is fully capable of differ- entiating among deionized (DI) water, phosphate buffered saline (PBS), ethanol and methanol in tes ts conducted at four different excitation frequencies of 50 MHz, 500 MHz, 1 GHz and 3 GHz. Further, dielectric readings of ethanol from the sensor interfaced with the IC at five excitation frequencies in the range of 50 MHz to 2 GHz are in excellent agreement (error <1%) with those from using a vector network analyzer (VNA) as the sensor readout. A bulk-solution reference measurement by an Agilent 85070E dielec- tric probe kit in