A cascade comprising multiple filters according to an embodiment comprises a filter, which includes a splitter configured to split an analog radio-frequency input signal into at least a first signal and a second signal, a first signal path configured to generate, based on the first signal, a time-delayed signal delayed by a predetermined delay time in the time domain, a second signal path configured to generate, based on the second signal, a phase-shifted signal shifted by a controllable predetermined phase shift in the phase domain, and a coupler configured to generate an output signal based on the time-delayed signal and the phase-shifted signal. Using an embodiment may improve a trade-off between frequency-related flexibility and frequency agility of a receiver infrastructure.

A feed forward echo cancellation device includes a first impedance circuit, a second impedance circuit, and an echo cancellation current generator circuit. The first impedance circuit is configured to output a first current to a node in response to a transmission current. The second impedance circuit is configured to output a second current to a node in response to the transmission current. The echo cancellation current generator circuit is configured to drain an echo cancellation current from the node. The node is connected to an input terminal of a programmable gain amplifier circuit via a gain control circuit, and the gain control circuit is configured to set a gain of the programmable gain amplifier circuit.

One or more aspects of the techniques and models described herein provide for bidirectional recurrent neural network (BiRNN)-based digital pre-distortion techniques for radio frequency (RF) power amplifiers (PAs). As an example, a digital pre-distorter (DPD) system may implement residual learning and long short-term memory (LSTM) projection layer features to reduce computational complexity and memory requirements. Implementing the described unconventional techniques of applying residual learning in RNN (e.g., in BiLSTM), using LSTM projection to develop a DPD structure, or both, may provide several advantages over preexisting techniques. For instance, the complexity in training and pre-distortion may be reduced and significantly less memory may be required to store the DPD neural network coefficients (e.g., while achieving similar or better linearization performance compared to other LSTM models). Further, faster training convergence speed may be achieved (e.g., compared to other LSTM models).

The present power amplifier linearizing module linearizes operation of a power amplifier and operates in parametrizing mode and operation mode. A processing module executes a feed-forward transfer functions set, which includes at least: a transfer function P and a summing function. The transfer function P derives a change signal ΔV.sub.a relative to the control signal component received and the summing function summing the incremental change signal ΔV.sub.a to an input signal to generate an adjusted input signal. A transfer function G uses the adjusted input signal to generate an RF signal representative of the amplifying of the adjusted input signal based on the control signal component. The processing module determines a linearizing control signal component based on the generated RF signal representative.

A radio frequency circuit includes a power amplifier configured to selectively amplify one of a first radio frequency signal and a second radio frequency signal that have different bandwidths, and when the first radio frequency signal is input to the power amplifier, a first bias signal is applied to the power amplifier, and when the second radio frequency signal is input to the power amplifier, a second bias signal different from the first bias signal is applied to the power amplifier.

Methods, systems, and devices for wireless communication are described. A communication device, such as a user equipment (UE) may receive a set of demodulation reference signal (DMRS) samples including a first subset of DMRS samples associated with a first power level and a second subset of DMRS samples associated with a second power level. The UE may perform a digital post distortion operation based on the first subset of DMRS samples associated with the first power level and the second subset of DMRS samples associated with the second power level. The UE may receive the wireless communication based on performing the digital post distortion operation.

An integrated circuit operable to measure an impedance presented to a transmitter path of the integrated circuit and a method thereof are provided. The integrated circuit includes a directional coupler that has an input port, a through port, a coupled port, and an isolation port. The integrated circuit also includes a power amplifier coupled to the input port of the directional coupler, a power detector configured to measure output levels from the coupled port and the isolation port of the directional coupler, a reference signal generator coupled to the isolation port of the directional coupler, and a vector modulator configured to adjust a phase of a signal generated from the power amplifier.

Envelope tracking systems for power amplifiers are provided herein. In certain embodiments, an envelope tracker is provided for a power amplifier that amplifies an RF signal. The envelope tracker includes a multi-level switching circuit having an output that provides an output current that changes in relation to an envelope signal indicating an envelope of the RF signal when the envelope tracker is operating in an envelope tracking mode. The multi-level switching circuit includes a multi-level supply (MLS) modulator that receives multiple regulated voltages of different voltage levels, and an MLS control circuit that controls the selection of the MLS modulator over time based on the envelope signal. When transitioning the MLS modulator from selection of one regulated voltage level to another regulated voltage level, the MLS control circuit provides a soft transition to gradually switch the regulated voltage levels.

Aspects of this disclosure relate to a multiplexer with a hybrid acoustic passive filter. The multiplexer includes a plurality of filters configured to filter respective radio frequency signals, a shared filter coupled between each of the plurality of filters and a common node, and a radio frequency filter coupled to the common node. At least a first filter of the plurality of filters includes acoustic resonators and a non-acoustic passive component. Related multiplexers, wireless communication devices, and methods are disclosed.

In some examples, a system includes a transceiver configured to transmit a first surveillance message at a first power level at or below a first maximum power level. The system also includes processing circuitry coupled to the transceiver, the processing circuitry configured to determine that a threshold condition exists. The processing circuitry is also configured to determine a second maximum power level in response to determining that the threshold condition exists, where the second maximum power level is lower than the first maximum power level. The transceiver is configured to transmit, in response to the processing circuitry determining that the threshold condition exists, a second surveillance message at a second power level, wherein the second power level is at or below the second maximum power level.