A multiple-stage amplifier includes a driver stage die and a final stage die. The driver stage die includes a first type of semiconductor substrate (e.g., a silicon substrate), a first transistor, and an integrated portion of an interstage impedance matching circuit. A control terminal of the first transistor is electrically coupled to an RF signal input terminal of the driver stage die, and the integrated portion of the interstage impedance matching circuit is electrically coupled between a current-carrying terminal of the first transistor and an RF signal output terminal of the driver stage die. The second die includes a III-V semiconductor substrate (e.g., a GaN substrate) and a second transistor. A connection, which is a non-integrated portion of the interstage impedance matching circuit, is electrically coupled between the RF signal output terminal of the driver stage die and an RF signal input terminal of the final stage die.

An RF amplifier is described including an input, an output, a parallel arrangement of a first branch and at least one further branch, each branch comprising a bipolar transistor in a degenerative emitter configuration having a base coupled to the input, a collector coupled to a common collector node, and an emitter degeneration impedance arranged between the emitter and a common rail. The common collector node is coupled to the output, the base of the first branch bipolar transistor is biased at a first bias voltage and the base of the at least one further branch bipolar transistor is biased at a bias voltage offset from the first bias voltage. In operation of the RF amplifier a IM3 distortion current output by the first branch bipolar transistor is in antiphase to a IM3 distortion current output by the at least one further branch bipolar transistor.

An RF amplifier is described including an input, an output, a parallel arrangement of a first branch and at least one further branch, each branch comprising a bipolar transistor in a degenerative emitter configuration having a base coupled to the input, a collector coupled to a common collector node, and an emitter degeneration impedance arranged between the emitter and a common rail. The common collector node is coupled to the output, the base of the first branch bipolar transistor is biased at a first bias voltage and the base of the at least one further branch bipolar transistor is biased at a bias voltage offset from the first bias voltage. In operation of the RF amplifier a IM3 distortion current output by the first branch bipolar transistor is in antiphase to a IM3 distortion current output by the at least one further branch bipolar transistor.

A circuit having an amplifier, comprising: a depletion mode transistor having a source electrode coupled to a reference potential; a drain electrode coupled to a potential more positive than the reference potential; and a gate electrode for coupling to an input signal. The circuit includes a bias circuit, comprising: a current source; and biasing circuitry coupled to the current source and between the potential more positive than the reference potential and a potential more negative than the reference potential. A control circuit is connected to the current source for controlling the amount of current produced by the current source to the biasing circuitry.

A circuit having an amplifier, comprising: a depletion mode transistor having a source electrode coupled to a reference potential; a drain electrode coupled to a potential more positive than the reference potential; and a gate electrode for coupling to an input signal. The circuit includes a bias circuit, comprising: a current source; and biasing circuitry coupled to the current source and between the potential more positive than the reference potential and a potential more negative than the reference potential. A control circuit is connected to the current source for controlling the amount of current produced by the current source to the biasing circuitry.

Systems, methods and apparatus for efficient power control and/or compensation with respect to a varying supply voltage of an RF amplifier for amplification of a constant envelope RF signal are described. A reduction in a size of a pass device of an LDO regulator is obtained by removing the pass device of the LDO regulator from a main current conduction path of the RF amplifier. Power control and/or compensation is provided by varying one or more gate voltages to cascoded transistors of a transistor stack of the RF amplifier according to a power control voltage. Various configurations for controlling the gate voltages are presented by way of a smaller size LDO regulator or by completely removing the LDO regulator. In a case where a supply voltage to the transistor stack varies, such as in a case of a battery, a compensation circuit is used to adjust the power control voltage in view of a variation of the supply voltage, and therefore null a corresponding drift/variation in output power of the RF amplifier.

Systems, methods and apparatus for efficient power control and/or compensation with respect to a varying supply voltage of an RF amplifier for amplification of a constant envelope RF signal are described. A reduction in a size of a pass device of an LDO regulator is obtained by removing the pass device of the LDO regulator from a main current conduction path of the RF amplifier. Power control and/or compensation is provided by varying one or more gate voltages to cascoded transistors of a transistor stack of the RF amplifier according to a power control voltage. Various configurations for controlling the gate voltages are presented by way of a smaller size LDO regulator or by completely removing the LDO regulator. In a case where a supply voltage to the transistor stack varies, such as in a case of a battery, a compensation circuit is used to adjust the power control voltage in view of a variation of the supply voltage, and therefore null a corresponding drift/variation in output power of the RF amplifier.

A semiconductor device includes a compound semiconductor layer, a gate electrode, and first and second insulating layers. The first insulating layer covers the gate electrode on the compound semiconductor layer and has a cavity that surrounds the gate electrode. The second insulating layer is provided on the first insulating layer and has an opening at a position corresponding to the cavity. A part of the second insulating layer, which is provided on the first insulating layer that covers the gate electrode, corresponding to the cavity is removed via the opening, so that the generation of parasitic capacitance due to the second insulating layer is suppressed.

A semiconductor device includes a compound semiconductor layer, a gate electrode, and first and second insulating layers. The first insulating layer covers the gate electrode on the compound semiconductor layer and has a cavity that surrounds the gate electrode. The second insulating layer is provided on the first insulating layer and has an opening at a position corresponding to the cavity. A part of the second insulating layer, which is provided on the first insulating layer that covers the gate electrode, corresponding to the cavity is removed via the opening, so that the generation of parasitic capacitance due to the second insulating layer is suppressed.

Certain aspects of the present disclosure provide methods and apparatus for amplifying signals with an amplification circuit. The amplification circuit generally includes a first transistor, an input path coupled between an input node of the amplification circuit and a control input of the first transistor, and a feedforward path coupled between the input node and a feedforward node. In certain aspects, the amplification circuit may also include a first resistive device coupled between the feedforward node and the control input of the first transistor, a biasing circuit coupled to the feedforward node, and a low-impedance path coupled to the feedforward node.