Development of a variable frequency impedance measuring system

In this paper, we present the design of a variable frequency AC impedance measuring system. We have implemented this into an on-board module as well as into CMOS circuitry using TSMC 0.35μm 2P4M Mixed Mode Process. The circuit consists of high output impedance “load-in-loop” Voltage-Controlled Current Source (VCCS), a high Common — Mode Rejection Ratio (CMRR) and high input impedance Instrumentation Amplifier (IA), voltage comparators, high pass filters, peak detectors, and XOR gate for phase detection. The onboard module is interfaced to a microcontroller (MCU) that is based on the Arduino platform. The MCU drives a Digital Direct Synthesis Sine Wave Generator (DDS-SWG) to generate the variable frequency input voltage that drives the VCCS.