Apparatus and methods for envelope tracking systems are disclosed herein. In certain implementations, an envelope tracking system for generating a power amplifier supply voltage for a power amplifier is provided. The envelope tracking system includes a DC-to-DC converter that generates a regulated voltage from a battery voltage and controls a voltage of the regulated voltage using a low frequency feedback signal. The envelope tracking system further includes an error amplifier that generates an output current using an envelope signal and a high frequency feedback signal. The low frequency feedback signal is based on a low frequency component of the power amplifier supply voltage and the high frequency feedback signal is based on a high frequency component of the power amplifier supply voltage. The error amplifier generates the power amplifier supply voltage by adjusting the magnitude of the regulated voltage using the output current.

A receiver includes a low noise amplifier (LNA) configured to amplify an input RF signal using a first current supplied by a first current source, and a voltage controlled oscillator (VCO) for applying an oscillation frequency to the amplified signal by generating an oscillation signal using the first current.

There is disclosed an envelope tracking modulated supply arranged to generate a modulated supply voltage in dependence on a reference signal, comprising a low frequency path for tracking low frequency variations in the reference signal and including a switched mode power supply, a correction path for tracking high frequency variations in the reference signal and including a linear amplifier, a feedback path from the output of the linear amplifier to the input of the linear amplifier, and a combiner for combining the output of the switched mode power supply and the output of the linear amplifier to generate a modulated supply voltage.

A PA power supply, which includes a first ET power supply, power supply control circuitry, a first PMOS switching element, and a second PMOS switching element, is disclosed. During a first operating mode, the power supply control circuitry selects an OFF state of the first PMOS switching element, selects an ON state of the second PMOS switching element, and adjusts a voltage of a first switch control signal to maintain the OFF state of the first PMOS switching element using a voltage at a source of the first PMOS switching element and a voltage at a drain of the first PMOS switching element; the PA power supply provides a first PA power supply signal; and the first ET power supply provides a first ET power supply signal, such that the first PA power supply signal is based on the first ET power supply signal.

There is disclosed an envelope tracking amplification stage comprising an input path and an envelope path and a delay stage in one of the input path and the envelope path, the delay of the delay stage being determined in dependence on the slope polarity of a signal representing the input and whether the signal in the input path leads or lags the signal in the envelope path.

In an embodiment an envelope modulator comprises a gain compensated lag-lead network or a gain compensated lead-lag network.

A predistortion processing apparatus: an auxiliary feedback module, configured to: extract a nonlinear distortion signal from an analog signal, and input an obtained feedback signal corresponding to the nonlinear distortion signal into an auxiliary model coefficient training module; the auxiliary model coefficient training module, configured to: train an auxiliary coefficient according to the feedback signal and a predistortion signal, and transmit a first auxiliary coefficient obtained through training to a predistortion processing module; a radio frequency signal feedback module, configured to extract a fundamental wave feedback signal; a predistortion model coefficient training module, configured to: train a predistortion coefficient according to the predistortion signal and the fundamental wave feedback signal, and transmit an obtained predistortion coefficient to the predistortion processing module; the predistortion processing module, configured to: perform predistortion processing on an input intermediate frequency signal by performing nonlinear modeling according to the first auxiliary coefficient and the predistortion coefficient.

An adaptive linearizer system includes an adaptive linearizer circuit that is configured to pre-distort an input signal based on one or more control signals to generate a pre-distorted signal, and a non-linear high-power amplifier (HPA) having non-linear characteristics that is coupled to the adaptive linearizer circuit. The nonlinear HPA amplifies the pre-distorted signal. The pre-distortion characteristics of the adaptive linearizer circuit provide for countering the non-linear characteristics of the non-linear HPA and compensating a non-linearity of the non-linear HPA.

Systems, methods and apparatus for efficient power control and/or compensation with respect to a varying supply voltage of an RF amplifier for amplification of a constant envelope RF signal are described. A reduction in a size of a pass device of an LDO regulator is obtained by removing the pass device of the LDO regulator from a main current conduction path of the RF amplifier. Power control and/or compensation is provided by varying one or more gate voltages to cascoded transistors of a transistor stack of the RF amplifier according to a power control voltage. Various configurations for controlling the gate voltages are presented by way of a smaller size LDO regulator or by completely removing the LDO regulator. In a case where a supply voltage to the transistor stack varies, such as in a case of a battery, a compensation circuit is used to adjust the power control voltage in view of a variation of the supply voltage, and therefore null a corresponding drift/variation in output power of the RF amplifier.

A multi-mode envelope tracking (ET) amplifier circuit is provided. The multi-mode ET amplifier circuit can operate in low-resource block (RB) mode and high-RB mode. The multi-mode ET amplifier circuit includes an ET amplifier(s) to amplify a radio frequency (RF) signal(s) to an amplified voltage, low-RB switcher circuitry to generate a direct current (DC) current, and high-RB switcher circuitry to generate an alternating current (AC) current. The amplified voltage, the DC current, and the AC current collectively cause the RF signal to be transmitted at a determined power. A control circuit(s) activates the high-RB switcher circuitry in the high-RB mode to provide the AC current, thus minimizing AC current sourced from the ET amplifier(s). As a result, it is possible to improve efficiency of the ET amplifier(s) and the multi-mode ET amplifier circuit in the high-RB mode and the low-RB mode.