Transimpedance amplifier circuit

A transimpedance amplifier circuit comprising:

• an amplifier circuit configured to convert an input current signal into a voltage signal with a gain being varied in accordance with a control signal;
• and
• a gain control circuit configured to generate the control signal in accordance with an amplitude of the voltage signal, the gain control circuit including:
• a detection circuit configured to generate an amplitude detection signal in accordance with the amplitude of the voltage signal,
• a setting circuit configured to generate an amplitude reference signal in accordance with a reference voltage,
• a differential voltage generation circuit configured to generate a differential voltage signal in accordance with a voltage difference between the amplitude detection signal and the amplitude reference signal, the differential voltage signal being offset from the voltage difference based on an amplitude setting signal,
• an operational transconductance amplifier (OTA) configured to generate a differential current signal in accordance with the differential voltage signal, and
• a variable capacitor circuit connected to an output of the OTA, the variable capacitor circuit having a variable capacitance being varied in accordance with the amplitude setting signal, and being configured to be charged and discharged by the differential current signal and output a charging voltage,
• wherein the control signal is generated in accordance with the charging voltage,
• wherein the differential voltage generation circuit includes a current source, a first transistor, a second transistor, a first resistor, and a second resistor,
• wherein the current source is connected to both a source of the first transistor and a source of the second transistor,
• wherein the amplitude detection signal is input to a gate of the first transistor and the amplitude reference signal is input to a gate of the second transistor,
• wherein the first resistor is connected between a drain of the first transistor and a grounding line, and the second resistor is connected between a drain of the second transistor and the grounding line,
• wherein the differential voltage signal is output from the drain of the first transistor and the drain of the second transistor,
• wherein the gain control circuit further includes a current generator configured to generate an offset current in accordance with a value indicated by the amplitude setting signal,
• wherein the differential voltage generation circuit further includes a third resistor connected between the first transistor and the grounding line, and
• wherein the offset current is input to a node between the first resistor and third resistor.