A charge amplifier includes an operational amplifier having first and second voltage dividers across its output connected to a capacitor and a resistor, respectively, in an R-C network returned to one input for magnifying the apparent value of the impedance of the capacitor and of the resistance of the resistor. Its output is also connected to an integrating network including another operational amplifier having its output supplied to a third voltage divider supplying signal to another input of the first operational amplifier. A pair of differentially coupled piezoelectric charge sources supply signal to the amplifier through filters and the second voltage divider has a portion shunted by a parallel connection of back-to-back diodes and another resistor for effectively attenuating response to low frequency signals.

A highpass feedback loop for A.C. coupled amplifier circuits is disclosed, by means of which pulse undershoot recovery is accelerated. The feedback loop includes an operational amplifier which goes into limiting above a selected amplitude threshold so that for pulses exceeding the threshold the amplifier frequency response is unaffected.

A method to increase the bandwidth of a transimpedance amplifier using capactive feedback. The resultant amplifier maintains wide bandwidth, high linearity, low noise, and low input impedance independent of component variations. These characteristics greatly facilitate the economical measurement of small currents such as those arising from photodiodes and biological preparations.

An infra-red receiver front-end includes a trans-impedance amplifier connected to receive an input current and provided with frequency selective transadmittance feedback between its output and input, the transadmittance feedback having a DC path to ground for low frequency noise components in the input current, caused by background illumination.

An image sensor driving circuit of the matrix driving type includes a plurality of sensor elements for converting light image information into an electrical image signal, an operational amplifier circuit section for amplifying the electrical image signal and a logic circuit section for controlling the operation of the amplifier circuit section. In one embodiment, the amplifier circuit section includes a single stage operational amplifier having a pair of series-connected feed-back resistors and a trimmer capacitor connected between the interconnection between the feed-back resistors and ground, which allows to eliminate the differential signal component arising from the parasitic capacitance of the sensor element. In another embodiment, the operational amplifier is provided with an input offset compensation circuit which supplies a compensation voltage opposite in polarity to the input offset voltage of the operational amplifier, thereby preventing crosstalk from occurring. In a further embodiment, the image sensor includes an analog circuit section having an operational amplifier circuit and a logic circuit section which are mounted on separate substrates.