An ultrasound probe buffer is provided. The ultrasound probe buffer may include a high impedance amplifier having a common-source core stage with series-series local feedback. The high impedance amplifier may include a first MOSFET and a second MOSFET, wherein a source terminal of the first MOSFET is coupled to a source terminal of the second MOSFET.

A low noise amplifier (LNA) system for amplifying a plurality of carriers includes a first amplifier circuit that generates a first radio-frequency (RF) output signal by amplifying a first input RF signal corresponding to a first frequency band, the first amplifier circuit having a first input impedance, and a second amplifier circuit that generates a second RF output signal by amplifying the first input RF signal when the system is in a first multi-output mode, a second input impedance of the second amplifier having a first impedance value when the system is in the first multi-output mode. The LNA system further includes a first impedance controller that maintains the second input impedance of the second amplifier circuit at a second impedance value when the apparatus is in a mode other than the first multi-output mode. The second impedance value is substantially the same as the first impedance value.

An integrated circuit comprises a first amplifier circuit with a push-pull amplifier configured to be calibrated to a low second order distortion. The integrated circuit further comprises a second amplifier circuit with at least one push-pull amplifier, wherein a size ratio between sizes of the transistors is adjustable by adjusting the size of at least one transistor device. The size ratio can be consecutively adjusted to a plurality of values, and for each value, a first output signal of a push-pull amplifier with an applied test signal and a second output signal of a push-pull amplifier without applied test signal, are determined. The size ratio for which a difference between the push-pull amplifier output signals is closest to zero is determined, and the push-pull amplifier of the first amplifier circuit is calibrated in dependence of the determined size ratio.

A radio frequency (RF) power transistor circuit includes a power transistor and a decoupling circuit. The power transistor has a control electrode coupled to an input terminal for receiving an RF input signal, a first current electrode for providing an RF output signal at an output terminal, and a second current electrode coupled to a voltage reference. The decoupling circuit includes a first inductive element, a first resistor, and a first capacitor coupled together in series between the first current electrode of the power transistor and the voltage reference. The decoupling circuit is for dampening a resonance at a frequency lower than an RF frequency.

Various implementations include systems for amplifying input signals. In particular implementations, a system includes a common mode voltage controller configured to receive an input signal and output a pair of adjusted signals; a modulator that generates a pair of pulse width modulation (PWM) signals in response to the adjusted signals; and a self-boosting push pull amplifier configured to receive the PWM signals and generate an amplified output, wherein the self-boosting push pull amplifier is configured to generate a differential mode voltage representative of an amplified version of the input signal, wherein the adjusted audio signals generated by the common mode voltage controller include a dynamically adjusted gain and duty cycle offset that causes the self-boosting push pull amplifier to operate with a reduced common mode voltage.

A differential amplifier circuit includes a first and second amplifiers that output a differential signal in a radio-frequency band, a first inductor having a first end connected to an output end of the first amplifier, a second inductor having a first end connected to an output end of the second amplifier, a choke inductor connected to second ends of the first and second inductors, a first and second capacitors, and a switch that connects the second capacitor in parallel to the first capacitor or terminates a parallel connection of the first and second capacitors. A resonant circuit formed by connecting the first or second inductor in series with the first capacitor has a different resonant frequency from a resonant circuit formed by connecting the first or second inductor in series with the parallel-connected first and second capacitors. These resonant frequencies correspond to second harmonic frequencies of the differential signal.

A filterless high-efficiency class D power amplifier (HEPA) exploits the phase relationships of even and odd harmonics at transistor drains of a push-pull topology to eliminate output filtering, enabling an ultra-high-efficiency, low harmonic signal. The filterless HEPA relieves the amplifier of a requirement for a power consuming filter by implementing a high-quality operational harmonic block on an output stage without output buffering. The operational harmonic block senses the voltage source radio frequency to the amplifier prior to waveform squaring and employs a harmonic canceling balun to block even harmonics (in-phase) but pass odd harmonics (180° out of phase). The sensed ideal voltage source shunts the odd-harmonic currents to ground, leaving only the fundamental current on its primary to pass to the load.

A semiconductor integrated circuit includes an input terminal, an output terminal, and a multi-stage connection unit including multiple MOS transistors connected in multiple stages between the input terminal and the output terminal. The MOS transistors include an input stage transistor connected to the input terminal and an output stage transistor connected to the output terminal. A thickness of a gate dielectric of the output stage transistor is equal to a thickness of a gate dielectric of the input stage transistor, and a gate length of the output stage transistor is longer than a gate length of the input stage transistor.

In some examples, a hybrid Chireix-Doherty amplifier comprises a first and second input network, a main amplifier coupled to a first output of the first input network, an auxiliary amplifier coupled to a second output of the second input network, and a combiner network. The combiner network is coupled to a first output of the main amplifier and an output of the auxiliary amplifier. The combiner network includes an output node for coupling to a load, e.g., an antenna of a base station for a radio network. The main amplifier is implemented as an inverse class-F amplifier.

A radio frequency (RF) power transistor circuit includes a power transistor and a decoupling circuit. The power transistor has a control electrode coupled to an input terminal for receiving an RF input signal, a first current electrode for providing an RF output signal at an output terminal, and a second current electrode coupled to a voltage reference. The decoupling circuit includes a first inductive element, a first resistor, and a first capacitor coupled together in series between the first current electrode of the power transistor and the voltage reference. The decoupling circuit is for dampening a resonance at a frequency lower than an RF frequency.