A filter circuit comprises in a signal line a band filter (BF) allowing to let pass a useful frequency band and a notch filter (NF) circuited in series to the band filter for filtering out a stop band frequency. The notch filter comprises a series circuit of a number of parallel shunt elements (SE1 . . . SE6) wherein each shunt element is shifted infrequency against the other shunt elements that the frequencies thereof are distributed (f1 . . . F6) over a notch band. All shunt elements may be realized as a SAW one-port resonator (TR.sub.NF) including regions with different pitches.

A system may include a first IQ modulator configured to: based on an I and a Q, produce a zero to ninety degree variable phase shifted output signal that changes relative to an input envelope of an RF drive waveform of the RF drive. The system may include a first amplifier path configured to: output a first phase modulated signal. The system may include a second IQ modulator configured to: based on the I and the −Q, produce a zero to negative ninety degree variable phase shifted output signal that changes relative to the input envelope. The system may include a second amplifier path configured to: output a second phase modulated signal, wherein the second phase modulated signal is complementary to the first phase modulated signal. The system may include a vector generator configured to: generate the Q and the −Q for the first and second IQ modulators, respectively.

A maximum current detection circuit with multiple input current ports and a maximum current port generates, on the maximum current port, a maximum current corresponding to the largest input current on one of the input current ports. The maximum current detection circuit includes multiple current mirror circuits, each controlled by one of the input currents. Each of the current mirror circuits includes outputs, each coupled to a respective one of the input current ports and the maximum current port. The current mirror circuit controlled by the largest input current becomes the dominant source for the input currents on each of the input current ports and also drives the maximum current on the maximum current port. The input currents may be single-ended or differential signals. The input currents may be respectively delayed signals of a windowing circuit in an envelope tracking circuit controlling a power amplifier of a wireless device.

An integrated circuit includes an oscillator and a power amplifier. The oscillator includes a first node, a second node, and a network of one or more reactive components coupled between the first node and the second node. The power amplifier includes a first input coupled to the first output of the oscillator, a second input coupled to the second output of the oscillator, and an output. The power amplifier includes a coarse gain control circuit, a first amplifier stage, and a second amplifier stage.

A power amplification circuit can include an input impedance matching circuit associated with one or more frequency bands of a plurality of frequency bands. The power amplification circuit can include a transistor with respective input coupled to an output of the input impedance matching circuit. The power amplification circuit can include a plurality of output impedance matching circuits. Each output impedance matching circuit can be associated with a respective frequency band of the plurality of frequency bands. The power amplification circuit can include a single pole multi-throw (SPMT) switch having an input terminal connected to an output of the transistor and a plurality of output terminals. Each output terminal of the SPMT switch can be connected to a corresponding output impedance matching circuit of the plurality of output impedance matching circuits.

A transmitter for a communication system comprises a digital pre-distortion (DPD) circuit and adaptation circuitry. The DPD circuit is configured to generate a digital intermediate signal by compensating an input signal for distortions resulting from an amplifier. The amplifier is configured to output an output signal based on the digital intermediate signal. The DPD circuit includes one or more an infinite impulse response (IIR) filters configured to implement a first transfer function based on a first parameter, and a second transfer function based on the first parameter and a time constant. The DPD circuit is configured to generate an adjustment signal based on the first transfer function and the second transfer function. The adaptation circuitry is configured to update the first parameter based on the adjustment signal, the input signal, and the output signal.

Systems and methods for a tunable impedance are provided. A tunable impedance includes a transistor assembly having two terminals and a control input. The transistor assembly includes one or more transistors electrically connected between the two terminals to provide a first impedance between the two terminals, based upon a control signal. One or more replica transistors react to the control signal in a similar fashion as the transistor assembly, to provide a replica impedance based upon the control signal. A control circuit is configured to generate the control signal based upon a voltage across the replica transistor(s) and/or a current through the replica transistor(s).

Embodiments of RF amplifiers and packaged RF amplifier devices each include an amplification path with a transistor die, and an output-side impedance matching circuit having a T-match circuit topology. The output-side impedance matching circuit includes a first inductive element (e.g., first wirebonds) connected between the transistor output terminal and a quasi RF cold point node, a second inductive element (e.g., second wirebonds) connected between the quasi RF cold point node and an output of the amplification path, and a first capacitance connected between the quasi RF cold point node and a ground reference node. The RF amplifiers and devices also include a baseband termination circuit connected to the quasi RF cold point node, which includes an envelope resistor, an envelope inductor, and an envelope capacitor coupled in series between the quasi RF cold point node and the ground reference node.

A multi-band power amplifier module includes at least one transmission input terminal, at least one power amplifier circuit that receives a first transmission signal and a second transmission signal through the at least one transmission input terminal, a first filter circuit that allows the first transmission signal to pass therethrough, a second filter circuit that allows the second transmission signal to pass therethrough, at least one transmission output terminal through which the first and second transmission signals output from the first and second filter circuits are output, a transmission output switch that outputs each of the first and second transmission signals output from the at least one power amplifier circuit to the first filter circuit or the second filter circuit, and a first tuning circuit that adjusts impedance matching between the at least one power amplifier circuit and the at least one transmission output terminal.

Envelope tracking power amplifiers with advanced gain shaping are provided. In certain implementations, a power amplifier system includes a power amplifier that amplifies a radio frequency (RF) signal and an envelope tracker that controls a voltage level of a supply voltage of the power amplifier based on an envelope of the RF signal. The power amplifier system further includes a gain shaping circuit that generates a gain shaping current that changes with the voltage level of the supply voltage from the envelope tracker. For example, the gain shaping circuit can include an analog look-up table (LUT) mapping a particular voltage level of the supply voltage to a particular current level of gain shaping current. Additionally, the gain shaping circuit biases the power amplifier based on the gain shaping current.