A circuit arrangement is provided which includes an array of stages for photon counting current to voltage conversion. Each stage includes a tunable operational transconductance amplifier and a feedback network forming a feedback loop of the operational transconductance amplifier. Each stage is configured to provide an output signal as a function of an input signal that is provided to the amplifier input of the operational transconductance amplifier, wherein the input signal comprises one or more current pulses and the output signal comprises one or more voltage pulses. With the tunable operational transconductance amplifier the transconductance of a stage can be tuned so that differences in peaking time and gain are avoided. Furthermore, an imaging device and a method for operating a circuit arrangement are provided.

An amplifier circuit with a high pass filter is constructed to include an operational amplifier (op amp) with a feedback loop in which a capacitor is in parallel with a field effect transistor (FET) configured as a gate tunneling resistor. To configure as a gate tunneling resistor, the source and drain of the FET are tied together, and large resistance is provided through the thin oxide layer between the gate and the source/drain. A bias voltage to the FET can be provided through a separate FET, also configured as a gate tunneling resistor. Additional gate tunneling FETs, also in parallel with the capacitor, can be switched into the circuit in order to provide different resistances, and thus different corner frequencies of the filter. Bias voltages may be supplied by one or more gate tunneling FETs. A fully differential op amp can have complementary feedback loops from its differential outputs, each feedback loop employing one or more gate tunneling FETs.