Improvement in linearity is achieved at low costs in a power amplifier module employing an envelope tracking system. The power amplifier module includes a first power amplifier circuit that amplifies a radio frequency signal and that outputs a first amplified signal, a second power amplifier circuit that amplifies the first amplified signal on the basis of a source voltage varying depending on amplitude of the radio frequency signal and that outputs a second amplified signal, and a matching circuit that includes first and second capacitors connected in series between the first and second power amplifier circuit and an inductor connected between a node between the first and second capacitors and a ground and that decreases a gain of the first power amplifier circuit as the source voltage of the second power amplifier circuit increases.

A radio frequency (RF) receiver that includes a low noise amplifier (LNA), a tunable resonant circuit, and a processor for performing calibration of the RF receiver. The processor is configured to sweep the tunable resonant circuit through a dynamic range of resonant frequency settings while estimating noise signal output power at the LNA at each setting. The processor is also configured to set the tunable resonant circuit to the setting that produces the greatest noise signal power output at the LNA.

A radio frequency (RF) receiver that includes a low noise amplifier (LNA), a tunable resonant circuit, and a processor for performing calibration of the RF receiver. The processor is configured to sweep the tunable resonant circuit through a dynamic range of resonant frequency settings while estimating noise signal output power at the LNA at each setting. The processor is also configured to set the tunable resonant circuit to the setting that produces the greatest noise signal power output at the LNA.

Aspects of this disclosure relate to efficient power amplifiers, such as class-F power amplifiers. A power amplifier transistor can provide an amplified RF signal. A termination can be coupled to an output of the power amplifier transistor and configured to provide a short circuit at a second harmonic. In some instances, the termination circuit can provide an open circuit at a third harmonic. A resonant circuit can be coupled to the output terminal of the power amplifier transistor and configured to provide an open circuit at the third harmonic. In certain embodiments, an input termination circuit coupled to an input terminal of the power amplifier transistor can provide a short circuit at the second harmonic. The power amplifiers of this disclosure can be implemented, for example, in envelope tracking applications.

An embodiment of an amplifier has a bandwidth defined by low and upper cutoff frequencies. The amplifier includes an input impedance matching circuit and a transistor. The transistor has a gate, a first current conducting terminal coupled to an output of the amplifier, and a second current conducting terminal coupled to a reference node. The input impedance matching circuit has a filter input coupled to an input of the amplifier, a filter output coupled to the gate of the transistor, and a multiple pole filter coupled between the filter input and the filter output. A first pole of the filter is positioned at a first frequency within the bandwidth, and a second pole of the filter is positioned at a second frequency outside the bandwidth. The input impedance matching circuit is configured to filter the input RF signal to produce a filtered RF signal at the filter output.

A parallel resonant circuit with excellent distortion and saturation characteristics is provided at low power consumption. A first power-supply voltage is applied to the parallel resonant circuit. In the parallel resonant circuit, a variable resistor includes one or more parallel-connected branches. Each of the branches includes a series circuit of a resistor and a MOS switch. A second power supply supplies power of control signals applied to respective gates of the MOS switches, and supplies back gate voltages to the MOS switches. A power-supply voltage of the second power supply is higher than the first power-supply voltage.

A parallel resonant circuit with excellent distortion and saturation characteristics is provided at low power consumption. A first power-supply voltage is applied to the parallel resonant circuit. In the parallel resonant circuit, a variable resistor includes one or more parallel-connected branches. Each of the branches includes a series circuit of a resistor and a MOS switch. A second power supply supplies power of control signals applied to respective gates of the MOS switches, and supplies back gate voltages to the MOS switches. A power-supply voltage of the second power supply is higher than the first power-supply voltage.

A notch filter including an inductor-capacitor tuning circuit is disclosed. The inductor-capacitor tuning circuit may determine a frequency response of the notch filter in accordance with an associated resonant frequency. In some exemplary embodiments, the inductor-capacitor circuit may include a differential inductor divided at a symmetry point and a variable capacitor coupled to the differential inductor at the symmetry point.

A bias circuit for applying bias current to a low quiescent current amplifier includes first and second transistors and a transistor pair circuit. The first transistor is connected to a supply bias voltage source and an auxiliary bias voltage source, and is controlled by a bias voltage output from the auxiliary bias voltage source, the first transistor acting as a current source. The second transistor is connected to the supply bias voltage source and an output of the first transistor, and is controlled by the output of the first transistor to selectively buffer supply bias current from the supply bias voltage source provided to the low quiescent current amplifier via a bias resistor. The transistor pair circuit includes third and fourth transistors connected in series, one of the third and fourth transistors is also connected in parallel with a dividing resistor, the transistor pair circuit acting as a voltage source.

Compression control of cascode power amplifiers. A power amplifier module can include a power amplifier including a cascode transistor pair. The cascode transistor pair can include a first transistor and a second transistor. The power amplifier module can include a current comparator configured to compare a first base current of the first transistor and a second base current of the second transistor to generate a comparison signal. The power amplifier module can include a saturation controller configured to maintain the power amplifier out of saturation based on the comparison signal.