An amplifier including a first cascode circuit including a first transistor and a second transistor whose source or emitter is coupled to a drain or a collector of the first transistor, a second cascode circuit being a differential pair with the first cascode circuit, the second cascode circuit including a third transistor whose source or emitter is coupled to a source or an emitter of the first transistor and a fourth transistor whose source or emitter is coupled to a drain or collector of the third transistor, a first feedback path that couples between an output terminal of the third transistor and an input terminal of the first transistor, the first feedback path including a first capacitative element, and a second feedback path that couples between an output terminal of the first transistor and an input terminal of the third transistor, the second feedback path including a second capacitative element.

An amplifier including a first cascode circuit including a first transistor and a second transistor whose source or emitter is coupled to a drain or a collector of the first transistor, a second cascode circuit being a differential pair with the first cascode circuit, the second cascode circuit including a third transistor whose source or emitter is coupled to a source or an emitter of the first transistor and a fourth transistor whose source or emitter is coupled to a drain or collector of the third transistor, a first feedback path that couples between an output terminal of the third transistor and an input terminal of the first transistor, the first feedback path including a first capacitative element, and a second feedback path that couples between an output terminal of the first transistor and an input terminal of the third transistor, the second feedback path including a second capacitative element.

A semiconductor device comprises a substrate and a high-electron-mobility transistor (HEMT). The substrate is formed with a recess. At least a portion of the HEMT is disposed in the recess. A method for manufacturing the semiconductor device is also disclosed. A radio frequency (RF) front-end module that employs the semiconductor device is also disclosed

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.

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.

A power amplification circuit includes: a first amplifier that is input with a first signal and outputs a second signal; a bias circuit that supplies a bias current or voltage to the first amplifier; and a control voltage generating circuit that generates a control voltage in accordance with the first signal. The bias circuit includes a first transistor that outputs the bias current or voltage, a second transistor provided between the emitter or source of the first transistor and ground, and a third transistor that is supplied with the control voltage and that supplies a first current or voltage to the second transistor. The value of the first current or voltage when the signal level is a first level is larger than the value of the first current or voltage when the signal level is a second level. The first level is higher than the second level.

A power amplification circuit includes: a first amplifier that is input with a first signal and outputs a second signal; a bias circuit that supplies a bias current or voltage to the first amplifier; and a control voltage generating circuit that generates a control voltage in accordance with the first signal. The bias circuit includes a first transistor that outputs the bias current or voltage, a second transistor provided between the emitter or source of the first transistor and ground, and a third transistor that is supplied with the control voltage and that supplies a first current or voltage to the second transistor. The value of the first current or voltage when the signal level is a first level is larger than the value of the first current or voltage when the signal level is a second level. The first level is higher than the second level.

A transceiver or RF front end employing a transformer with a low loss transmit/receive (T/R) switch circuit in the ground path. In various embodiments, differential outputs of a power amplifier are coupled to the first winding of the transformer, while the input of a low noise amplifier is coupled to the second side of the transformer via a matching inductor. The T/R switch circuit, which may be a thin oxide CMOS transistor, is coupled between the second side of the transformer and ground. In operation, the T/R switch circuit may be enabled during transmit mode operations of the power amplifier, such that a low impedance path to ground is provided at the input of the low noise amplifier, thereby protecting it from high voltage swings generated by the power amplifier.

A transceiver or RF front end employing a transformer with a low loss transmit/receive (T/R) switch circuit in the ground path. In various embodiments, differential outputs of a power amplifier are coupled to the first winding of the transformer, while the input of a low noise amplifier is coupled to the second side of the transformer via a matching inductor. The T/R switch circuit, which may be a thin oxide CMOS transistor, is coupled between the second side of the transformer and ground. In operation, the T/R switch circuit may be enabled during transmit mode operations of the power amplifier, such that a low impedance path to ground is provided at the input of the low noise amplifier, thereby protecting it from high voltage swings generated by the power amplifier.

Packaged RF transistor amplifiers are provided that include a flat no-lead overmold package that includes a die pad, a plurality of terminal pads and an overmold encapsulation that at least partially covers the die pad and the terminal pads and an RF transistor amplifier die mounted on the die pad and at least partially covered by the overmold encapsulation. These packaged RF transistor amplifiers may have an output power density of at least 3.0 W/mm.sup.2.