A Wideband Low-Power LC-DCO-Based Complex Dielectric Spectroscopy System in 0.18- $\mu \text{m}$ CMOS

Abstract

A low-power integrated LC-oscillator-based broadband dielectric spectroscopy (BDS) system is presented. The real relative permittivity ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ' is measured as a shift in the oscillator frequency using an on-chip frequency-to-digital converter. The imaginary relative permittivity ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> " increases the losses of the oscillator tank which mandates a higher dc biasing current to preserve the same oscillation amplitude. An amplitude-locked loop is used to fix the amplitude and linearize the relation between the oscillator bias current and ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> " . The proposed BDS system employs a sensing oscillator and a reference oscillator where correlated double sampling is used to mitigate the impact of flicker noise, temperature variations, and frequency drifts. A prototype is implemented in 0.18-μm CMOS process with a total chip area of 6.24 mm2 to operate in 1-6-GHz range using three dual bands LC oscillators. The total power consumption ranges from 10 to 24 mW depending on the operating frequency. The sensor measures complex permittivity within 2% accuracy for the real part ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ' and 5% for the imaginary part ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ". The achieved standard deviation in the air is 2.1 ppm for frequency reading and 110 ppm for current reading.