An integrated charge amplifier for a smart tactile sensor

Abstract

A novel circuit for read-out of a sensor capacitance is presented. This circuit is generally referred to as a charge amplifier, and is implemented in a bipolar full-custom design for the accumulation of tactile data from a tactile imaging sensor. A capacitance is measured with two local feedback Miller capacitances in a trans-impedance amplifier, whereby the output signal is a direct measure of the deflecting capacitance. The performance of this circuit is estimated theoretically and measurements prove its capability to detect capacitance changes of 15–20 fF from a nominal capacitance of 1.25–2.5 pF. This new design features a reduced number of circuit components, provided that they are properly selected to minimize their inherent effect on the transfer and linearity of the amplifier. It is shown that the charge amplifier can be included in a capacitive pressure imaging array with high spatial resolution. An additional circuit element to select the tactile data from a prototype pressure-sensitive touch array is reported as a preliminary experiment for the construction of a fully-integrated intelligent capacitive tactile sensor.