An apparatus includes an input transformer, an amplifier and an output transformer. The input transformer may be on a substrate and configured to convert an input signal into a differential input signal. The input signal may be a radio-frequency signal. The amplifier may be on the substrate and configured to generate a differential output signal in response to the differential input signal. The amplifier may be a balanced and distributed amplifier. The output transformer may be on the substrate and configured to convert the differential output signal into an output signal. Each of the input transformer and the output transformer may be a three line coupled balun transformer with a variable bandpass bandwidth.

A data modulation apparatus may comprise a S2D conversion part including a first amplifier operating based on a carrier wave signal and two transformers receiving an output signal of the first amplifier; a first switch part transferring status of input data to the first amplifier based on the input data; a differential amplification part receiving output signals of the S2D conversion part and amplifying the output signals of the S2D conversion part; a D2S conversion part receiving output signals of the differential amplification part and performing modulation on the output signals by converting the output signals to a single signal; and a second switch part transferring the output signals of the differential amplification part to the D2S conversion part based on the input data. Here, the first switch part and the second switch part may be alternately turned on and off.

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.

A compensation circuit of a power amplifier includes a varactor, a voltage sensor and a control circuit. The varactor is coupled to an input terminal of the power amplifier. The voltage sensor is arranged for detecting an amplitude of an input signal of the power amplifier to generate a detecting result. The control circuit is coupled to the varactor and the voltage sensor, and is arranged for controlling a bias voltage of the varactor to adjust a capacitance of the varactor according to the detecting result.

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.

A push-pull amplifier includes a pair of active devices driving the primary side of a double distributed active transformer (DDAT). The primary side of the DDAT includes a cascaded arrangement of primary windings of a first set of transformers with the active devices coupled ends of cascaded arrangement of primary windings. The secondary side of the DDAT includes a cascaded arrangement of secondary windings of a second set of transformers coupled to a load. Secondary windings of the first set of transformers drive inputs of respective active stages. Outputs of the active stages drive respective primary windings of the second set of transformers.

A compensation circuit of a power amplifier includes a varactor, a voltage sensor and a control circuit. The varactor is coupled to an input terminal of the power amplifier. The voltage sensor is arranged for detecting an amplitude of an input signal of the power amplifier to generate a detecting result. The control circuit is coupled to the varactor and the voltage sensor, and is arranged for controlling a bias voltage of the varactor to adjust a capacitance of the varactor according to the detecting result.

A power amplifier system includes a differential power amplifier and a bias circuit. The differential power amplifier is arranged for receiving a differential input pair to generate an output signal. The bias circuit is arranged for generating a bias voltage to bias the differential power amplifier, and the bias circuit comprises a source follower for receiving a reference voltage to generate the bias voltage.

A push-pull amplifier includes a pair of active devices driving the primary side of a double distributed active transformer (DDAT). The primary side of the DDAT includes a cascaded arrangement of primary windings of a first set of transformers with the active devices coupled ends of cascaded arrangement of primary windings. The secondary side of the DDAT includes a cascaded arrangement of secondary windings of a second set of transformers coupled to a load. Secondary windings of the first set of transformers drive inputs of respective active stages. Outputs of the active stages drive respective primary windings of the second set of transformers.