The present invention generally relates to a structure and method of audio amplifier by dynamic impedance adjustment, including a power amplifying unit, a loud-speaker, a current sensing unit and a subtraction unit. The power amplifying unit has a fixed closed loop gain, with an input side and an output side; the loud-speaker is electrically connected to the output side of the power amplifying unit; the current sensing unit senses the output current of the power amplifying unit, and the sensed output current is converted into a current control voltage signal; the subtraction unit inputs the audio voltage signal and the feedback current control voltage signal, and outputs the difference of the audio voltage signal minus the current control voltage signal, and inputs it to the input side of the power amplifying unit. The output sound quality of the loud-speaker is improved by dynamic impedance adjustment.

Apparatus and methods for a no-load-modulation power amplifier are described. No-load-modulation power amplifiers can comprise multiple amplifiers connected in parallel to amplify a signal that has been divided into parallel circuit branches. One of the amplifiers can operate as a main amplifier in a first amplification class and the remaining amplifiers can operate as peaking amplifiers in a second amplification class. The main amplifier can see essentially no modulation of its load between the power amplifier's fully-on and fully backed-off states. The power amplifiers can operate in symmetric and asymmetric modes. Improvements in bandwidth and drain efficiency over conventional Doherty amplifiers are obtained. Further improvements can be obtained by combining signals from the amplifiers with hybrid couplers.

An outphasing amplifier includes a first class-E power amplifier (16-1) having an output coupled to a first conductor (31-1) and an input receiving a first RF drive signal (S.sub.1(t)). A first reactive element (C.sub.A-1) is coupled between the first conductor and a second conductor (30-1). A second reactive element (L.sub.A-1) is coupled between the second conductor and a third conductor (32-1). A second class-E power amplifier (17-1) includes an output coupled to a fourth conductor (31-2) and an input coupled to a second RF drive signal (S.sub.2(t)), a third reactive element (C.sub.A-3) coupled between the second and fourth conductors. Outputs of the first and second power amplifiers are combined by the first, second and third reactive elements to produce an output current in a load (R). An efficiency enhancement circuit (L.sub.EEC-1) is coupled between the first and fourth conductors to improve power efficiency at back-off power levels. Power enhancement circuits (20-1,2) are coupled to the first and fourth conductors, respectively.

An embodiment of a radio-frequency (RF) device includes at least one transistor, a package, and a surface-mountable capacitor. The package contains the at least one transistor and includes at least one termination. The surface-mountable capacitor is coupled in a shunt configuration between the at least one transistor and a power supply terminal of the device to decouple the at least one transistor from a power supply.

Radio frequency (RF) amplification devices are disclosed that include Doherty amplification circuits and methods of operating the same. In one embodiment, a Doherty amplification circuit includes a main carrier RF amplifier, a peaking RF amplifier, and a periodic quadrature coupler. To provide Doherty amplification, the peaking RF amplifier is configured to be deactivated while an RF signal is below a threshold level and is configured to be activated while the RF signal is above the threshold level. The periodic quadrature coupler is configured to combine a first RF split signal from the main carrier RF amplifier and a second RF split signal from the peaking RF amplifier into the RF signal, such that the RF signal is output from an output port while the peaking RF amplifier is activated. The periodic quadrature coupler allows the Doherty amplification circuit to provide broadband amplification in various RF communication bands.

A power amplifier comprising an amplifying element for amplifying a signal input to the amplifier, a matching network for varying the reactance presented to the output of the amplifying element at the fundamental frequency of the input signal, the matching network being switchable between first and second operating configurations, wherein in the first operating configuration, a net inductive reactance is presented to the output at the fundamental frequency and in the second operating configuration, a net capacitive reactance is presented to the output at the fundamental frequency.

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.

A power amplifier system for amplifying an input having a carrier frequency having an amplitude. The system includes a plurality of n amplifiers coupled to an asymmetrical combiner formed of a passive network, each amplifier has an input and an output, the asymmetrical combiner has a plurality of inputs and an output, the output of each amplifier is coupled to an input of the asymmetrical combiner, an impedance viewed at the output of each of the n amplifiers is a function of the amplitude and phase at each of the other n−1 amplifiers. An amplitude/phase controller is coupled to the plurality of n amplifiers or the asymmetrical combiner to control the amplitude/phase at the asymmetrical combiner input. The amplitude/phase controller is configured to present an amplitude/phase at each input of the asymmetrical combiner to target an optimal impedance at the carrier frequency for each of the plurality of n amplifiers.

An embodiment of a Doherty amplifier module includes a substrate, an RF signal splitter, a carrier amplifier die, and a peaking amplifier die. The RF signal splitter divides an input RF signal into first and second input RF signals, and conveys the first and second input RF signals to first and second splitter output terminals. The carrier amplifier die includes one or more first power transistors configured to amplify, along a carrier signal path, the first input RF signal to produce an amplified first RF signal. The peaking amplifier die includes one or more second power transistors configured to amplify, along a peaking signal path, the second input RF signal to produce an amplified second RF signal. The carrier and peaking amplifier die are coupled to the substrate so that the RF signal paths through the carrier and peaking amplifier die extend in substantially different (e.g., orthogonal) directions.

An RF matrix switch has a first set of card slots at selected locations on the chassis and a second set of card slots at different selected locations on the chassis as well as input cards and output cards. The input cards, the output cards, the first set of card slots and the second set of card slots are all configured so that the input cards and the output cards fit into all of these slots. Reroute cards can be provided for any unused card slots. The RF matrix switch also may have an active power management system in which there is a power control switch connected to each amplifier that turns the amplifier off when the amplifier is not being used.