Circuits, methods and devices are disclosed, related to fast turn-on of radio-frequency (RF) amplifiers. In some embodiments, an RF amplifier circuit includes an amplification path implemented to amplify an RF signal, where the amplification path includes a switch and an amplifier. In some embodiments, each of the switch and the amplifier are configured to be ON or OFF to thereby enable or disable the amplification path, respectively. In some embodiments, the RF amplifier circuit includes a compensation circuit coupled to the amplifier, where the compensation circuit is configured to compensate for a slow transition of the amplifier between its ON and OFF states resulting from a signal applied to the switch.

A differential amplifier which does not have an effect of noise resistance deterioration, waveform distortion, and a lower bandwidth while having a wide input range is realized. The differential amplifier does not cause deterioration in a signal quality due to an increase in an input load, and it is not necessary to additionally provide a configuration for generating a reference voltage. The differential amplifier includes a differential amplification circuit and an output circuit for amplifying and outputting a differential output from the differential amplification circuit. The differential amplification circuit includes a first conductive type first differential pair which supplies output currents according to a positive phase input signal and a reverse phase input signal to the output circuit, a second conductive type second differential pair which supplies output currents according to a positive phase input signal and a reverse phase input signal to the output circuit, a detector which detects an operation state of a differential pair, and an alternative current supplying circuit which supplies an alternative current for the output current of the differential pair which has been turned off to the output circuit.

A Class-D amplifier includes a plurality of power rails, a quantizer, and a driver stage. The quantizer and the driver stage have a combined gain. For each power rail of the plurality of power rails, the Class-D amplifier senses a voltage value for the power rail and determines a ramp amplitude based on the sensed voltage value. The Class-D amplifier concurrently switches from the driver stage using a first power rail to a second power rail of the plurality of power rails and switches from the quantizer using the ramp amplitude associated with the first power rail to using the ramp amplitude associated with the second power rail so that the combined gain is constant.

A gate bias circuit for a plurality of GaAs amplifier stages is a transistor coupled to a temperature compensation current received from a CMOS control stage. A plurality of pHEMPT amplifier stages are coupled to the gate bias circuit and to a control voltage which switches the amplifier stage. A selectively controlled stage pass transistor enables a current mirror between the gate bias circuit and each stage amplifying transistor. The penultimate pHEMPT amplifier stage is coupled to a CMOS amplifier. A CMOS circuit provides both the temperature compensation current by a proportional to absolute temperature (PTAT) circuit and the control voltage enabling each pHEMPT transistor to receive its input signal in combination with the gate bias voltage.

Gain is suppressed. In a power amplification circuit, a first transistor has a first input terminal, a first output terminal, and a first ground terminal. A second transistor has a second input terminal, a second output terminal, and a second ground terminal. The second input terminal is connected to the first input terminal. The second output terminal is connected to the first output terminal. A first bias circuit is connected to the first input terminal. A second bias circuit is connected to the second input terminal. A first resistor is connected between the first ground terminal and the ground. A second resistor is connected between the second ground terminal and the ground. The second resistor has a resistance value greater than that of the first resistor.

Methods and apparatus for providing adaptive biasing to power amplifiers. Adaptive bias circuits are configured to provide sharp turn on and/or current clamping to improve the efficiency of a power amplifier over a wide input signal bandwidth. Sharp turn on may be achieved using a subtraction technique to subtract outputs from multiple detectors. Clamping may be achieved using MOSFET device characteristics to pull the device from the triode region into the saturation, subtraction techniques to subtract the outputs from multiple detectors, and/or by using circuit devices, such as diodes.

The present disclosure provides example power amplifier combiner apparatuses and power amplifier circuits. One example power amplifier combiner apparatus includes a signal processing unit and n power amplifier units. The signal processing unit is separately coupled to input terminals of the n power amplifier units. Output terminals of the n power amplifier units are separately coupled to a load. When an output power of the power amplifier combiner apparatus is less than a first threshold, the signal processing unit controls a first power amplifier unit to operate. When the output power is greater than or equal to an i.sup.th threshold and is less than an (i+1).sup.th threshold, the signal processing unit controls the first i+1 power amplifier units to operate. When the output power is not less than an (n−1).sup.th threshold, the signal processing unit controls the n power amplifier units to operate, where i=1, . . . , or n−2.

A direct current (DC)-DC converter that includes a first switching converter and a multi-stage filter is disclosed. The multi-stage filter includes at least a first inductance (L) capacitance (C) filter and a second LC filter coupled in series between the first switching converter and a DC-DC converter output. The first LC filter has a first LC time constant and the second LC filter has a second LC time constant, which is less than the first LC time constant. The first LC filter includes a first capacitive element having a first self-resonant frequency, which is about equal to a first notch frequency of the multi-stage filter.

A pulse shaping circuit is configured to shape a waveform of an edge of a signal applied to a switch of a power amplifier included in an on-off keying transmitter.

An amplifier may include control circuitry that may track a first input signal parameter and, in response, adjust a value of a second input parameter. Input parameter tracking and adjustment may facilitate control of output parameters for the amplifier. For example, an envelope-tracking amplifier may track input signal amplitude and adjust other input parameters in response. The adjustments may facilitate control of output parameters, such as gain or efficiency. The amplifier may further include calibration circuitry to determine adjustment responses to various tracked input parameters.