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.

A power amplification module includes: an amplifier that amplifies an input signal and outputs an amplified signal; and a harmonic-termination circuit to which harmonics of the amplified signal are input and the impedance of which is controlled in accordance with the frequency of a harmonic. The power amplification module can operate in a first mode in which a power supply voltage changes in accordance with the average voltage value of the amplified signal over a prescribed time period or in a second mode in which the power supply voltage changes in accordance with the envelope of the input signal. The impedance of the harmonic-termination circuit is controlled such that at least one even-ordered harmonic is short-circuited when the power amplification module operates in the first mode and at least one odd-ordered harmonic of third order or higher is short-circuited when the power amplification module operates in the second mode.

A power amplifier including: a main power amplification device having an output; an auxiliary power amplification device having an output; a load modulation circuit operably connected to the output of the main power amplification device and the output of the auxiliary power amplification device; and a post-matching circuit operably connected to load modulation circuit. The load modulation circuit is arranged to enable fundamental frequency load modulation and to enable modulated harmonic terminations of at least the second and third harmonic frequencies. The modulated harmonic terminations may include drain terminations.

A low-noise amplifier is provided. The low-noise amplifier includes a first transistor configured to amplify an input signal; a second transistor which forms a cascade structure with the first transistor and configured to amplify an output signal of the first transistor; and a third transistor which forms a cascode structure together with the first transistor and configured to amplify the output signal of the first transistor, wherein a first signal including a sum of the output signal of the second transistor and the output signal of the third transistor is output to an output terminal.

A class D amplifier output stage including an input for receiving an input signal, an output for providing an output signal to a load, serially coupled upper and lower switching devices configured to provide an output signal to the output, a driver circuit configured to receive the input signal, and to derive therefrom first and second drive signals for driving the upper and lower switching devices alternately from a conducting state into a non-conducting state and vice versa, such that the conducting state periods of the upper switching device with respect to those of the lower switching device are mutually exclusive and separated by dead time intervals during which both upper and lower output transistors are non-conducting. To reduce distortion and more particularly, total harmonic distortion (THD), the amplifier output stage includes a substantially linear circuit configured to provide a bidirectional current sink for residual currents from the load occurring during at least part of each dead time interval.

A high frequency amplifier circuit includes a transistor including a drain, a gate, and a source, an inductance-capacitor (LC) tank connected to the drain, and a transformer connected to the gate and the source.

A super-efficient single-stage switching power amplifier is realized by not incorporating a rectification process in its power conversion loop while incorporating a bidirectional active clamping circuit to not only remove or maximally reduce otherwise occurring disruptive ringing and spikes but also convert the energy otherwise associated with the ringing and spikes to return energy that goes back to the DC power supply.

Embodiments of radio frequency (RF) front-end circuitry are disclosed where the RF front-end circuitry includes a tunable RF filter structure and a calibration circuit. The tunable RF filter structure includes (at least) a pair of weakly coupled resonators and defines a transfer function with a passband. The calibration circuit is configured to shape the passband so that the passband defines a center frequency. Additionally, the calibration circuit is configured to detect a phase difference at the target center frequency between the pair of weakly coupled resonators and adjust the phase difference of the pair of weakly coupled resonators at the target center frequency so as to reduce a frequency displacement between the center frequency of the passband and the target center frequency. In this manner, the calibration circuit calibrates the tunable RF filter structure to correct for errors in the center frequency of the passband due to component manufacturing variations.

Certain aspects of the present disclosure provide an amplifier for signal amplification. Certain aspects further describe methods and apparatus for applying overload protection for such amplifier. For example, one method generally includes detecting an overload condition of an amplifier based on a signal at a node of the amplifier, and controlling a parameter of an input signal of the amplifier such that the parameter of the input signal is maintained below a threshold based on the detection of the overload condition. The parameter of the input signal may include, for example, a voltage level or a duty cycle of the input signal.

Certain aspects of the present disclosure provide methods and apparatus for dynamically managing the dead time between turning on output power stage transistors in amplifiers, such as audio amplifiers. One example method of operating an amplifier generally includes generating a drive signal based on an input signal; amplifying the drive signal by alternatively driving a first transistor and a second transistor with a time between deactivating the first transistor and activating the second transistor; and adjusting the time based on a parameter of the input signal or the drive signal, during the amplifying. For example, the parameter may include an amplitude of the input signal, a duty cycle of the drive signal, or a duty cycle of a modulated signal (e.g., a pulse-width modulated signal) generated based on the input signal. The input signal may be a digital audio input signal.