A CMOS Self-Contained Quadrature Signal Generator for SoC Impedance Spectroscopy

Abstract

This paper presents a low-power fully integrated quadrature signal generator for system-on-chip (SoC) impedance spectroscopy applications. It has been designed in a 0.18 μm-1.8 V CMOS technology as a self-contained oscillator, without the need for an external reference clock. The frequency can be digitally tuned from 10 to 345 kHz with 12-bit accuracy and a relative mean error below 1.7%, thus supporting a wide range of impedance sensing applications. The proposal is experimentally validated in two impedance spectrometry examples, achieving good magnitude and phase recovery results compared to the results obtained using a commercial LCR-meter. Besides the wide frequency tuning range, the proposed programmable oscillator features a total power consumption lower than 0.77 mW and an active area of 0.129 mm2, thus constituting a highly suitable choice as stimulation module for instrument-on-a-chip devices.

Current/Voltage Controlled Quadrature Sinusoidal Oscillators for Phase Sensitive Detection Using Commercially Available IC

“…Generally, the electrical signal generated from the sensors include the noises which come from many sources, for example, power systems, pre-amplifiers, thermal noises, etc. Phase sensitive detection is used to detect and measure a very low level electrical signal from the sensor [1][2][3]. The principle of the dual phase sensitive detection system is shown in Figure 1.…”

“…The quadrature sinusoidal oscillator generates the pure sinusoidal waves, v o1 (sine wave) and v o2 (cosine wave) with a 90 degree phase difference. The sine wave v o1 is fed to the impedance sensor Z S , which is connected to an auto-balancing bridge circuit consisting of an op-amp and a feedback resistor Z F [1]. The auto-balancing bridge circuit provides the output v z = A Z sin(ωt + θ z ), where A z and θ z are the amplitude and phase related to the resistance and reactance components of impedance sensor Z s .…”

“…The signal v z is sent to multiply with the sine wave v o1 and cosine wave v o2 . Then, the DC component is taken out by the lowpass filter (LPF) circuit, following v x and v y [1]:…”

“…Equations (1) and (2) show that v x and v y are the real and imaginary components of the impedance sensor [1].…”

“…Equations (1) and (2) show that vx and vy are the real and imaginary components of the impedance sensor [1]. The quadrature sinusoidal oscillator can be designed to achieve the electronic controllability for modern control systems.…”