A working state adjustment method is applied to a terminal. A power amplifier (PA) is arranged on the terminal. The method includes: determining a target channel bandwidth in which the terminal works; determining a target working state in which the PA works among optional working states according to the target channel bandwidth, in which the optional working states correspond to at least two types of working modes respectively; and adjusting the PA to work in the target working state.

Power amplifiers with adaptive bias for envelope tracking applications are provided herein. In certain embodiments, an envelope tracking system includes a power amplifier that amplifies a radio frequency (RF) signal and that receives power from a power amplifier supply voltage, and an envelope tracker that generates the power amplifier supply voltage based on an envelope of the RF signal. The power amplifier includes a field-effect transistor (FET) for amplifying the RF signal, and a current mirror including an input that receives a reference current and an output connected to the power amplifier supply voltage. An internal voltage of the current mirror is used to bias the gate of the FET to compensate the FET for changes in the power amplifier supply voltage arising from envelope tracking.

An amplifier comprises: an input stage, a pulse width modulation stage, and a switched output stage. During operation, the input stage receives an input signal (such as an audio signal). The input stage adjusts the input signal based on feedback from the switched output stage of the amplifier. According to one configuration, the feedback from the switched output stage is a voltage across a flying capacitor disposed in the switched output stage. The pulse width modulation stage uses the adjusted input signal or signals to produce respective pulse width modulation signals that are subsequently used to drive (control) switches in the switched output stage. The switches in the switched output stage generate an output voltage to drive a load based on states of the pulse width modulation signals. Adjustments applied to the input signal based on the feedback maintains the magnitude of the flying capacitor voltage at a desired setpoint.

An amplifier circuit includes an amplifier and an output transistor. The amplifier is coupled to an output node of the output transistor for providing an output voltage to a load device. The amplifier circuit also includes a slew-rate control circuit coupled to a gate node of the output transistor and configured to control voltage rise of the gate node of the output transistor during power-up to reduce output voltage overshoot.

A rectifier stage includes a differential input transistor pair coupled between a reference voltage node and an intermediate node, and a load circuit coupled between the intermediate node and a supply voltage node. The differential input transistor pair receives a radio-frequency amplitude modulated signal. A rectified signal indicative of an envelope of the radio-frequency amplitude modulated signal is produced at the intermediate node. An amplifier stage coupled to the intermediate node produces an amplified rectified signal at an output node that is indicative of the envelope of the radio-frequency amplitude modulated signal. The rectifier stage includes a resistive element coupled between the intermediate node and the supply voltage node in parallel to the load circuit.

Methods, systems, and devices for operating an amplifier with a controllable pull-down capability are described. A memory device may include a memory array and a power circuit that generates an internal signal for components in the memory array. The power circuit may include an amplifier and a power transistor that is coupled with the amplifier. A pull-down capability of the amplifier may be controllable using an external signal that is based on a difference between a reference signal and the internal signal. The power circuit may also include a comparator that is coupled with the amplifier and configured to compare the reference signal and the internal signal. Components of the comparator may be integrated with components of the amplifier, may share a bias circuit, and may use nodes within the amplifier to control the comparator. A signal output by the comparator may control the pull-down capability of the amplifier.

A system and method which includes receiving an input signal and providing, by an amplifier circuit, an output signal in response to the input signal, the output signal having an envelope. An envelope detection signal corresponding to the envelope of the output signal is generated. A bias current provided to an amplifier circuit is adjusted based upon the envelope detection signal. The amplifier circuit includes an amplifier and a transformer, the transformer being configured to establish a magnetically coupled feedback loop from an output of the amplifier to an input of the amplifier.

Disclosed is an operational amplifier based on a metal-oxide TFT. The operational amplifier includes an auxiliary amplifier and a bootstrap gain-increasing amplifier. The auxiliary amplifier adopts a two-stage positive feedback structure, including a fifth transistor, a seventh transistor, an eleventh transistor, a first amplifying unit, and a second amplifying unit. A gate of the fifth transistor serves as an input end of the operational amplifier. The bootstrap gain-increasing amplifier includes two second circuits in mutual symmetry. Each of the second circuits includes a first transistor, a second transistor, and a current source unit with a bootstrap structure.

A circuit is provided. In some examples, the circuit includes a first transistor having a gate and a drain coupled together and a current source coupled to the drain of the first transistor. A second transistor has a drain coupled to a source of the first transistor. A third transistor has a gate coupled to the gate of the first transistor. A fourth transistor has a drain coupled to a source of the third transistor and a gate of the fourth transistor is coupled to a gate of the second transistor. In some examples, the third transistor is configured to limit a first current between the third transistor and the fourth transistor based on an output voltage.

In one embodiment, a dual-mode power amplifier that can operate in different modes includes: a first pair of metal oxide semiconductor field effect transistors (MOSFETs) to receive and pass a constant envelope signal; a second pair of MOSFETs to receive and pass a variable envelope signal, where first terminals of the first pair of MOSFETs are coupled to first terminals of the second pair of MOSFETs, and second terminals of the first pair of MOSFETs are coupled to. second terminals of the second pair of MOSFETs; and a shared MOSFET stack coupled to the first pair of MOSFETs and the second pair of MOSFETs.