This implementation exhibits greatly reduced chargefeedthrough, and circuit behaviour is in accordance with a modification to the firstorder analysis that includes the effects of chargefeedthrough.
Importantly, no frequency locking and much reduced jitter is observed.
The main motivation being: to realize simple frontends for capacitive sensors and microsystems for integration in high-density sensing applications, for example, in arrays of sensors for highresolution ultrasound imaging.
In addition, there are many applications where a high accuracy in sensing is not essential; in such cases, a simple interface circuit can not only save the design time, but may also offer area and power advantages over the more complex circuits.
The first interface circuit is the realization of a current-mode approach that has the main advantage of being able to produce a fully-differential output also from a single-ended sensor by using just a fixed reference capacitor.
The circuit, prototyped in a commercial 0.8-µm CMOS process, was estimated capable of achieving an accuracy of around 0.2% relative to full-scale which may be sufficient in many applications.
In addition, parasitic induced jitter and frequency locking are identified as a second source of error.
The three interface circuits are implemented as an integrated circuit using the European Silicon Structures (ES2) ASIC CMOS process, with a modification to permit the inclusion of fullcustom designed, chargefeedthrough compensated switches.