Open-loop Spectrum Analyzer Integrated Circuit for Nanoresonator Sensing

A nanoresonator can be applied as a biochemical sensor based on the change in the mass of the nanoresonator, and the mass change can be interpreted in the frequency domain. In this paper, we present an open-loop spectrum analyzer integrated circuit (IC) for a nanoresonator. The circuit determines the frequency characteristics of a nanoresonator, such as quality factor (Q-factor) and resonant frequency, and detects minute resistance changes of the nanoresonator that result in changes in Q-factor or resonant frequency. The proposed nanoresonator driver circuit is implemented using an open-loop system, and to characterize the open-loop frequency response of the nanoresonator, the IC includes a voltage-controlled oscillator, a transimpedance amplifier, and a 16-bit delta-sigma analog-to-digital converter. To compensate for the parasitic components that cause the distortions of the phase and magnitude response, a shunt-capacitance cancelling amplifier is used to cancel the effect of the shunt-parasitic capacitance of the nanoresonator. The simulated target nanoresonator is modeled using the Butterworth-Van Dyke equivalent circuit model with a resonant frequency of 10 MHz. The proposed nanoresonator driver circuit is fabricated using a standard 0.18 mu m complementary metal oxide semiconductor process with an active area of 2.346 mm(2). The simulated resistive sensitivity of the IC is 5.1 mV/k Omega.