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

A low-power integrated <italic>LC</italic>-oscillator-based broadband dielectric spectroscopy (BDS) system is presented. The real relative permittivity <inline-formula> <tex-math notation="LaTeX">$\varepsilon _{r}^{\prime }$ </tex-math></inline-formula> is measured as a shift in the oscillator frequency using an on-chip frequency-to-digital converter. The imaginary relative permittivity <inline-formula> <tex-math notation="LaTeX">$\varepsilon _{r}^{\prime \prime }$ </tex-math></inline-formula> 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 <inline-formula> <tex-math notation="LaTeX">$\varepsilon _{r}^{\prime \prime }$ </tex-math></inline-formula>. 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-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS process with a total chip area of 6.24 mm² to operate in 1–6-GHz range using three dual bands <italic>LC</italic> 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 <inline-formula> <tex-math notation="LaTeX">$\varepsilon _{r}^{\prime }$ </tex-math></inline-formula> and 5% for the imaginary part <inline-formula> <tex-math notation="LaTeX">$\varepsilon _{r}^{\prime \prime }$ </tex-math></inline-formula>. The achieved standard deviation in the air is 2.1 ppm for frequency reading and 110 ppm for current reading.