A radio-frequency circuit includes a power amplifying circuit configured to amplify a first radio-frequency signal having a first channel bandwidth and a second radio-frequency signal having a second channel bandwidth greater than the first channel bandwidth. The power amplifying circuit is configured to amplify the first radio-frequency signal in an amplifying mode according to an average power tracking method, and to amplify the second radio-frequency signal in an amplifying mode according to an envelope tracking method.

An example apparatus includes: a compensation circuit including: a current compensation output, a first transistor with a first current terminal and a first control terminal, the first current terminal coupled to the current compensation output, and a resistor ladder with a tap terminal coupled to the first control terminal, a current mirror circuit having a mirror input and a mirror output, the mirror input coupled to the current compensation output, and a rectification circuit having an input coupled to the mirror output.

Envelope tracking systems for power amplifiers are provided herein. In certain embodiments, an envelope tracker supplies power to a power amplifier that amplifies an RF signal. The envelope tracker includes a multi-level switching circuit that generates an output current based on an envelope signal indicating an envelope of the RF signal. The envelope tracker further includes a combiner that combines a DC voltage with the output current of the multi-level switching circuit to generate a power amplifier supply voltage for the power amplifier. Accordingly, the output current of the multi-level switching circuit and a DC voltage are combined to generate the power amplifier supply voltage. Implementing the envelope tracking system in this manner can provide enhanced efficiency and/or higher bandwidth relative to an envelope tracking system in which a multi-level switching circuit directly outputs a power amplifier supply voltage.

This application relates to Class D amplifier circuits. A modulator controls a Class D output stage based on a modulator input signal (Dm) to generate an output signal (Vout) which is representative of an input signal (Din). An error block, which may comprise an ADC, generates an error signal (ε) from the output signal and the input signal. In various embodiments the extent to which the error signal (ε) contributes to the modulator input signal (Dm) is variable based on an indication of the amplitude of the input signal (Din). The error signal may be received at a first input of a signal selector block. The input signal may be received at a second input of the signal selector block. The signal selector block may be operable in first and second modes of operation, wherein in the first mode the modulator input signal is based at least in part on the error signal; and in the second mode the modulator input signal is based on the digital input signal and is independent of the error signal. The error signal can be used to reduce distortion at high signal levels but is not used at low signal levels and so the noise floor at low signal levels does not depend on the component of the error block.

An envelope tracking system has an envelope tracker that is configured to generate a power amplifier supply voltage that changes is relation to an envelope of a radio frequency signal, and a power amplifier comprises at least a first amplification stage having an input terminal receiving a radio frequency (RF) signal to be amplified. The power amplifier has a first coupling unit, and a second coupling unit inductively coupled with the first coupling unit, the second coupling unit provides radio frequency-coupled feedback to the input terminal of the first amplification stage through a radio frequency-coupled feedback path.

A mobile device can have a transceiver configured to generate a radio frequency signal and a power management system with envelope tracking. The device can also have a power amplifier system having a driver transistor coupled to a radio frequency signal input, a transformer balun having a main primary coil connected between the driver transistor and a voltage supply node of the power amplifier system, a secondary coil magnetically coupled to the main primary coil and an additional primary coil configured to generate a feedback signal related to a signal of the main primary coil. The power amplifier system can also have a push-pull amplifier with a first transistor having a base connected to a first end of the secondary coil and a second transistor having a base connected to a second end of the secondary coil. Accordingly, push-pull stage neutralization can deploy two transistors cross-connected to opposite ends of an output coil in a transformer balun.

A Doherty amplifier system is disclosed. The Doherty amplifier system includes a carrier amplifier having a carrier input and a carrier output, and a peaking amplifier having a peaking input coupled to the carrier input and a peaking output coupled to the carrier output. Analog pre-distortion circuitry is configured to linearize the carrier amplifier and linearize the peaking amplifier by compensating for base-to-collector capacitance loading of the carrier amplifier and the peaking amplifier during operation.

Multi-level envelope tracking systems are provided. In certain embodiments, an envelope tracking system includes a first power amplifier that amplifies a first radio frequency (RF) signal and receives power from a first power amplifier supply voltage, a second power amplifier that amplifies a second RF signal and receives power from a second power amplifier supply voltage, and an envelope tracker including a first modulator that controls the first power amplifier supply voltage based on a plurality of regulated voltages and a first envelope signal corresponding to an envelope of the first RF signal, a second modulator that controls the second power amplifier supply voltage based on the regulated voltages and a second envelope signal corresponding to an envelope of the second RF signal, and a switching point adaptation circuit that controls a voltage level of at least one of the regulated voltages based on a radio frequency power level.

Envelope tracking systems with modeling for power amplifier supply voltage filtering are provided herein. In certain embodiments, an envelope tracking system includes a supply voltage filter, a power amplifier that receives a power amplifier supply voltage through the supply voltage filter, and an envelope tracker that generates the power amplifier supply voltage. The power amplifier provides amplification to a radio frequency (RF) signal that is generated based on digital signal data, and the envelope tracker generates the power amplifier supply voltage based on an envelope signal corresponding to an envelope of the RF signal. The envelope tracking system further includes digital modeling circuitry that models the supply voltage filter and operates to digitally compensate the digital signal data for effects of the supply voltage filter, such as distortion.

Bias circuits and methods for silicon-based amplifier architectures that are tolerant of supply and bias voltage variations, bias current variations, and transistor stack height, and compensate for poor output resistance characteristics. Embodiments include power amplifiers and low-noise amplifiers that utilize a cascode reference circuit to bias the final stages of a cascode amplifier under the control of a closed loop bias control circuit. The closed loop bias control circuit ensures that the current in the cascode reference circuit is approximately equal to a selected multiple of a known current value by adjusting the gate bias voltage to the final stage of the cascode amplifier. The final current through the cascode amplifier is a multiple of the current in the cascode reference circuit, based on a device scaling factor representing the relative sizes of the transistor devices in the cascode amplifier and in the cascode reference circuit.