A device may include a voltage-to-current converter circuit having an operational transconductance amplifier (OTA), the voltage-to-current converter circuit for generating a bias current that is proportional to a reference voltage at a reference voltage input port of the OTA, and a bias current feedback path for providing the bias current to a bias current input port of the OTA. The device may further include a startup current generator circuit coupled to the bias current input port of the OTA, the startup current generator circuit controllable to provide a startup current to the bias current input port during a startup of the device and to be deactivated after the startup of the device.

An operational amplifier and a differential amplifying circuit thereof. The differential amplifying circuit receives a differential input signal and outputs a differential output signal. The differential amplifying circuit includes an output port that has a first terminal and a second terminal, the differential output signal being outputted via the first and second terminals; a first transistor pair receiving the differential input signal via two first ends and coupling to the first and second terminals respectively via two second ends; a second transistor pair receiving the differential input signal via two first ends and coupling to the first and second terminals respectively via two second ends; and a third transistor pair receiving a control signal via two first ends and coupling to the first and second terminals respectively via two second ends. The control signal controls the third transistor pair to switch on or off and/or controls the current flowing therethrough.

A circuit includes a differential input pair stage including bipolar transistors and configured to receive an RF input signal; a cascode stage coupled between the differential input pair stage and an output node, the cascode stage including bipolar transistors; and a current source including a first bipolar transistor coupled to a first output of the differential input pair stage and a second bipolar transistor coupled to a second output of the differential input pair stage.

An operational amplifier and a differential amplifying circuit thereof. The differential amplifying circuit receives a differential input signal and outputs a differential output signal. The differential amplifying circuit includes an output port that has a first terminal and a second terminal, the differential output signal being outputted via the first and second terminals; a first transistor pair receiving the differential input signal via two first ends and coupling to the first and second terminals respectively via two second ends; a second transistor pair receiving the differential input signal via two first ends and coupling to the first and second terminals respectively via two second ends; and a third transistor pair receiving a control signal via two first ends and coupling to the first and second terminals respectively via two second ends. The control signal controls the third transistor pair to switch on or off and/or controls the current flowing therethrough.

A circuit includes a differential input pair stage including bipolar transistors and configured to receive an RF input signal; a cascode stage coupled between the differential input pair stage and an output node, the cascode stage including bipolar transistors; and a current source including a first bipolar transistor coupled to a first output of the differential input pair stage and a second bipolar transistor coupled to a second output of the differential input pair stage.