ABSTRACT
This chapter explores how to design custom instrumentation to improve the signal-to-noise ratio of capacitance and impedance measurements. It focuses on a sensing scheme based on a transimpedance amplifier and a lock-in amplifier for the advantages of this approach in terms of sensitivity and flexibility. Transimpedance amplifiers, in which the signal current made available by the Device under Test (DUT) is converted into a voltage for further processing, are an excellent choice to perform impedance or capacitance spectroscopy. The conductive strips and the bonding pads required to electrically connect the DUT are capacitively coupled with the silicon substrate giving spurious impedance in parallel with the DUT. The dual-channel LIA simultaneously acquires the DUT signal and the reference signal that in this case is the stimulus signal. Very high-resolution measurements in the range of a few ppm require a special care for the reduction of slow gain fluctuations of the analog and analog/digital components.
