An adjustable gain power amplifier, a gain adjustment method and a mobile terminal are disclosed. The adjustable gain power amplifier comprises an input matching circuit, a gain adjustment circuit, a biasing circuit, a main amplification circuit, and an output matching circuit; the input matching circuit is connected between an input end and the gain adjustment circuit; the gain adjustment circuit is connected between the input matching circuit and the input end of the main amplification circuit; the output end of the main amplification circuit is connected to the output matching circuit, a positive power source end thereof is connected to a power supply source, a negative power source end thereof is connected to the biasing circuit; the biasing circuit provides different biasing voltages for the main amplification circuit; and the gain adjustment circuit and the biasing circuit are respectively connected to a gain adjustment control voltage (Vctrl).

A limiter circuit is integrated into an RF power amplifier. The limiter circuit automatically starts adding attenuation at the input of the RF power amplifier after a predetermined input power level threshold is exceeded, thereby extending the safe input drive level to protect the amplifier. In a preferred embodiment of the invention, the limiter circuit is implemented using a pseudomorphic high electron mobility transistor (PHEMT) device or a metal semiconductor field effect transistor (MESFET) device. Diode connected transistors or Schottky diodes may also be used in the limiter circuit.

Certain aspects of the present disclosure generally relate to an amplification circuit. The amplification circuit generally includes: a first amplification path comprising a first amplification transistor and coupled between an input node of the amplification circuit and an output node of the amplification circuit; and a second amplification path comprising a second amplification transistor and coupled between the input node and the output node, wherein the second amplification path further includes an attenuator coupled between the input node of the amplification circuit and a control input of the second amplification transistor.

A high frequency circuit includes a signal input terminal and a signal output terminal; a first amplifier, a second amplifier, a third amplifier, and a fourth amplifier; and a first phase shift circuit. An input terminal of the fourth amplifier is connected to the signal input terminal, an output terminal of the fourth amplifier is connected to an input terminal of the first amplifier and an input terminal of the second amplifier, an output terminal of the second amplifier is connected to an input terminal of the third amplifier, an output terminal of the third amplifier is connected to one end of the first phase shift circuit, and the other end of the first phase shift circuit is connected to an output terminal of the first amplifier.

This radiofrequency power limiter includes at least one transistor, a drain of the transistor being directly connected to a mesh connecting an input to an output of the limiter, a source of the transistor being connected to a common reference potential, and a gate of the transistor being connected to a common control potential. The transistor is not biased between its drain and its source during operation of the limiter.

Apparatus (301) for switchable attenuation of a differential input signal from a microphone includes positive and negative non-attenuating paths (406, 410) have n- and p-type MOSFETs (421, 422, 423, 424) in back-to-back configurations; positive and negative attenuating paths (405, 409) have n- and p-type MOSFETs (415, 416, 418, 419) in back-to-back configurations in combination with resistors; a gate driver (425) applies a drive signal of one polarity (QNEG) to gates of the n-type MOSFETs in the attenuating paths and the p-type MOSFETs in the non-attenuating paths, and a drive signal of opposite polarity (QPOS) to the gates of the p-type MOSFETs in the attenuating paths and the n-type MOSFETs in the non-attenuating paths; and the state of the MOSFETs depends on the drive signals at their gates, and thus the input signal may be routed via either the non-attenuating paths or the attenuating paths by controlling the drive signals.

A headphone driver, a sound processor that incorporates the headphone driver and a computing system that incorporates the headphone driver are provided. The headphone driver includes an amplifier having an input terminal and an output terminal, an R-2R ladder network provided with an input signal and connected to the input terminal of the amplifier, and a feedback resistor group connected to the input terminal and to the output terminal of the amplifier. The R-2R ladder network includes a plurality of resistor branches and a first attenuator that is connected between the plurality of resistor branches.

An energy-efficient consumer device audio power output stage with gain control provides improved battery life and reduced power dissipation without clipping the audio output signal. A control circuit controls a power supply that supplies the power supply rails to the power amplified output stage. The voltage of the power supply rails is controlled in conformity with an input audio signal level, which may be determined from a volume control setting of the device and/or from a signal level detector that determines the amplitude of the signal being amplified. The gain applied to the audio input signal is reduced for a predetermined time period when a higher output voltage of the power supply is selected, to avoid clipping the audio output signal.

A gain control circuit, having an attenuator including first to n-th (n>2) attenuator parts that attenuate an input signal respectively in accordance with first to n-th attenuation control signals to thereby generate an attenuated input signal, a signal amplifier configured to amplify the attenuated input signal, a detector circuit configured to conduct an envelope detection on the amplified attenuated input signal to thereby obtain an amplitude value, a comparator circuit configured to compare the amplitude value with a reference threshold value to thereby generate a comparison result signal, and an attenuator control circuit configured to generate the first to n-th attenuation control signals using the comparison result signal. The attenuation control signals indicate first to n-th attenuation amounts by which the first to n-th attenuator parts respectively attenuate the input signal, and first to n-th time periods during which the first to n-th attenuator parts respectively operate.

Power amplifier having analog pre-distortion by adaptive degenerative feedback. In some embodiments, a pre-distortion circuit for an amplifier can include a transistor having an input node for receiving an input signal, an output node for providing an output signal having a gain relative to the input signal, and a common node for coupling to a ground. The pre-distortion circuit can further include a degeneration circuit implemented between the common node and the ground, with the degeneration circuit being configured to introduce a feedback response that reduces the gain when the input signal has a power level at or below a selected level. The degeneration circuit can be further configured to be disabled or provide a reduced feedback response when the input signal has a power level that exceeds the selected level.