Multi-level envelope trackers with an analog interface are provided herein. In certain embodiments, an envelope tracking system for generating a power amplifier supply voltage for a power amplifier is provided. The envelope tracking system includes a multi-level supply (MLS) DC-to-DC converter that outputs multiple regulated voltages, and an MLS modulator that controls selection of the regulated voltages over time based on an analog envelope signal corresponding to an envelope of the RF signal amplified by the power amplifier.

An automatic gain control system for a receiver, including: an automatic gain control loop (40) adapted to be coupled to both a first transimpedance amplifier (12) coupled to a first analog-to-digital converter (14) forming a first tributary and a second transimpedance amplifier (12) coupled to a second analog-to-digital converter (14) forming a second tributary; and an offset gain control voltage to gain balance a transimpedance amplifier gain of the first tributary and a transimpedance amplifier gain of the second tributary. The automatic gain control loop can be analog. Also, the automatic gain control loop can be implemented in hardware or firmware.

An efficient baseband predistortion linearization method for reducing the spectral regrowth and compensating memory effects in wideband communication systems using effective multiplexing modulation technique such as wideband code division multiple access and orthogonal frequency division multiplexing is disclosed. The present invention is based on the method of piecewise pre-equalized lookup table based predistortion, which is a cascade of a lookup table predistortion and piecewise pre-equalizers.

The present disclosure is a novel utility of a software defined radio (SDR) based Distributed Antenna System (DAS) that is field reconfigurable and support multi-modulation schemes (modulation-independent), multi-carriers, multi-frequency bands and multi-channels. The present invention enables a high degree of flexibility to manage, control, enhance, facilitate the usage and performance of a distributed wireless network such as Flexible Simulcast, automatic traffic load-balancing, network and radio resource optimization, network calibration, autonomous/assisted commissioning, carrier pooling, automatic frequency selection, frequency carrier placement, traffic monitoring, traffic tagging, pilot beacon, etc. As a result, a DAS in accordance with the present invention can increase the efficiency and traffic capacity of the operators' wireless network.

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.

Embodiments disclosed herein relate to improving a power output of a transmitter of an electronic device. To do so, the transmitter may include signal selection circuitry to adjust a sign selection signal to accurately transition between polarities of a quadrature (e.g., I or Q) component signal stored in or for which an indication is stored in a storage cell of a radio frequency digital-to-analog converter. The sign selection signal may generate a separate adjusted sign selection signal for each polarity of each quadrature component signal such that a transition of the selection signal between a first value and a second value (e.g., logic high and low) occurs when the respective quadrature (e.g., +/− and I/Q) component signal is a logic low. In this way, the signal selection circuitry reduces an error pulse in the output of the transmitter.

A system for time aligning widely frequency spaced signals includes a digital predistortion (DPD) processor and a power amplifier coupled to the DPD processor and operable to provide a transmit signal at a power amplifier output. The system also includes a feedback loop coupled to the power amplifier output. The feedback loop comprises an adaptive fractional delay filter, a delay estimator coupled to the adaptive fractional delay filter, and a DPD coefficient estimator coupled to the delay estimator.

Apparatus and methods for bias switching of power amplifiers are provided herein. In certain configurations, a power amplifier system includes a power amplifier that provides amplification to a radio frequency (RF) signal, a power management circuit that controls a voltage level of a supply voltage of the power amplifier, and a bias control circuit that biases the power amplifier. The power management circuit is operable in multiple supply control modes, such as an average power tracking (APT) mode and an envelope tracking (ET) mode. The bias control circuit is configured to switch a bias of the power amplifier based on the supply control mode of the power management circuit.

A radio frequency transmitter includes N transmit channels, where each transmit channel includes one nonlinear module, a primary correction circuit, coupled to each of N nonlinear modules that correspond to the N transmit channels, and configured to provide a primary correction signal for the N nonlinear modules, and N secondary correction circuits, where the N secondary correction circuits are coupled to the N nonlinear modules respectively, and each secondary correction circuit is configured to provide a secondary correction signal for a nonlinear module coupled to the secondary correction circuit.

Apparatus and methods for power amplifier bias modulation for multi-level supply envelope tracking are provided herein. In certain embodiments, an envelope tracking system includes a power amplifier that amplifies a radio frequency signal, a multi-level supply envelope tracker that generates a power amplifier supply voltage of the power amplifier based on an envelope signal indicating an envelope of the radio frequency signal, and a bias modulation circuit that modulates a bias of the power amplifier based on a voltage level of the power amplifier supply voltage.