A broadband biosensor interface IC for miniaturized dielectric spectroscopy from MHz to GHz

Abstract

This paper describes a broadband biosensor interface IC as part of a miniaturized measurement platform currently under development for MHz-to-GHz dielectric spectroscopy (DS). Developed in 0.35μm 2P/4M RF CMOS, the IC measures the frequency-dependent S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> magnitude and phase of a microfabricated microfluidic dielectric sensor, when the sensor is loaded with a solution-under-test (SUT). The IC architecture implements a modified frequency response analysis (FRA) method by first down-converting the biosensor response signal from the RF excitation frequency to an intermediate frequency (IF) of 1MHz using an 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 lowpass filter (LPF). Dielectric readings of ethanol from the biosensor interfaced with the IC at five excitation frequencies in the range of 50MHz to 2GHz are in excellent agreement (error <; 1%) with those from using a vector network analyzer (VNA) as the sensor readout. A reference measurement by an Agilent 85070E dielectric probe kit is also included to show proof-of-concept feasibility in miniaturization.