A Broadband Sensor Interface IC for Miniaturized Dielectric Spectroscopy From MHz to GHz

Abstract

This paper describes a broadband sensor interface IC as part of a miniaturized measurement platform for MHz-to-GHz dielectric spectroscopy. Developed in 0.35 μm 2P/4M RF CMOS, the IC measures frequency-dependent S 21 magnitude and phase of a microfluidic 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 the RF excitation frequency to an intermediate frequency (IF) of 1 MHz using a low-noise amplifier (LNA) and active mixer, followed by down-converting the IF signal to dc using a coherent detector employing IF amplification stages with programmable gain, a passive mixer driven by in-phase (I) and quadrature-phase (Q) signals and an active-RC low-pass filter (LPF). The sensor interfaced with the IC is fully capable of differentiating among deionized (DI) water, phosphate buffered saline (PBS), ethanol and methanol in tests 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 dielectric probe kit interfaced with a VNA is also performed to verify proof-of-concept feasibility in conducting MHz-to-GHz dielectric spectroscopy with a miniaturized measurement platform using μL-sample volumes.