Wireless circuitry can include a processor that generates a reference baseband signal, an upconversion circuit that upconverts the baseband signals to radio-frequency signals, an amplifier that amplifies the radio-frequency signals, and an antenna. The amplifier can be adjusted based on an estimated value computed using error vector magnitude (EVM) estimation circuitry. The EVM estimation circuitry may include a first filter configured to receive the reference signal, a second filter configured to receive a measured signal coupled from the output of the amplifier, a first signal extraction circuit coupled to an output of the first filter, a second signal extraction circuit coupled to an output of the second filter, and a comparison circuit having a first input that receives signals from the first signal extraction circuit, a second input that receives signals from the second signal extraction circuit, and an output on which the estimated value is provided.

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 controls a voltage level of the power amplifier supply voltage based on an envelope of the RF signal. The power amplifier includes a current mirror having an input that receives a reference current, an output electrically connected to the power amplifier supply voltage, and a node that outputs a gate bias voltage. The power amplifier further includes a field-effect transistor that amplifies the radio frequency signal and a first depletion-mode transistor having a gate connected to the node of the current mirror and a source connected to a gate of the field-effect transistor.

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.

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.

A signal envelope detector is provided. The signal envelope detector includes an input node configured to receive an input signal. Further, the signal envelope detector includes a capacitive voltage divider coupled to the input node and configured to generate an attenuated input signal by voltage division of the input signal. The signal envelope detector additionally includes a source follower transistor coupled between a first node configured to receive a first voltage supply signal and a second node configured to receive a second voltage supply signal. A gate terminal of the source follower transistor is coupled to the capacitive voltage divider and configured to receive the attenuated input signal. The signal envelope detector includes a rectifier circuit configured to receive and rectify an output signal of the source follower transistor. In addition, the signal envelope detector includes a low-pass filter coupled to the rectifier circuit and configured to generate an envelope signal indicative of a rectified envelope of the input signal by low-pass filtering of an output signal of the rectifier circuit.

A voltage dividing capacitor circuit includes first capacitor through third capacitor dividers and first through fourth load capacitors. The first capacitor divider includes a first flying capacitor and a plurality of first switches connected in series between a first voltage node and a ground node, and is connected to a second voltage node. The second capacitor divider is connected to the first voltage node, the second voltage node, and a first intermediate voltage node. The third capacitor divider is connected to the second voltage node, the ground voltage node, and a second intermediate voltage node. The first through fourth load capacitors are connected in series between the first voltage node and the ground node. The second capacitor divider includes a second flying capacitor and a plurality of second switches connected in series between the first voltage node and the second voltage node.

An envelope tracking system includes an envelope tracking digital baseband (ETDBB) circuit, a digital-to-analog converter circuit, and an envelope tracking supply modulator (ETSM) circuit. The ETDBB circuit performs envelope detection upon a transmit (TX) baseband signal to generate an envelope detection result, and generates a digital envelope input according to the envelope detection result. The digital-to-analog converter circuit converts the digital envelope input into a supply envelope signal. The ETSM circuit generates a modulated supply voltage according to the supply envelope signal, and outputs the modulated supply voltage to a power amplifier. At least one of the ETDBB circuit and the ETSM circuit dynamically adjusts gain compression (GC) of the PA in response to a number of active resource blocks (RBs) in a channel bandwidth.

An envelope stacking power amplifier system reduces current for a given output power level without sacrificing the ability to support large voltage swings at saturation and therefore increases efficiency at the maximum linear operating power and all power levels below that. The system includes a stack/unstack controller including circuitry configured to switch the RF power amplifier system between a stacked mode in which first and second RF amplifiers are coupled in a stacked configuration and an unstacked mode in which the first and second RF amplifiers are coupled in an unstacked configuration in response to one or more mode-control signals, the stacked configuration providing reduced current compared to the unstacked configuration.

Apparatus and methods for envelope tracking systems are provided. In certain configurations, an envelope tracking system includes a digital filter that generates a filtered envelope signal based on a digital envelope signal representing an envelope of a radio frequency signal, a buck converter controllable by the filtered envelope signal and including an output electrically connected to a power amplifier supply voltage, a digital-to-analog converter module including an output electrically connected to the output of the buck converter and that provides an output current, and a digital shaping and delay circuit configured to generate a shaped envelope signal based on shaping the filtered envelope signal. The shaped envelope signal controls a magnitude of the output current, and the digital shaping and delay circuit controls a delay of the shaped envelope signal to align the output of the digital-to-analog converter module and the output of the buck converter.

The present invention breaks up the frequency bands which can be filtered by a simple low-loss band-pass or low pass filter. The second harmonic frequency is reduced by use of a non-linear clipper element which controls the driving waveform symmetry and can reduce the harmonics by as much as 5-15 db which makes the filter much simpler and allows the amplifier to remain wide-band. The output waveform from the amplifier is symmetrical or nearly symmetrical.