An amplifier circuit includes a primary differential amplifier circuit connected to receive a differential input and provide a primary differential output with a first non-linearity. A secondary differential amplifier circuit is connected to receive the differential input. The secondary differential amplifier circuit is configured to generate a secondary differential output with a second non-linearity. The secondary differential output and the primary differential output are coupled together with opposing polarities such that the second non-linearity cancels out at least the first non-linearity.

A power amplifier circuit includes a first amplifier transistor, a first nonlinear element, and a current control circuit. The first amplifier transistor has a base or a gate into which a first signal is input, a collector or a drain from which a signal resulting from amplification of the first signal is output, and an emitter or a source that is grounded. The first nonlinear element is connected between the collector or the drain of the first amplifier transistor and the base or the gate of the first amplifier transistor. The current control circuit is connected between the ground and the base or the gate of the first amplifier transistor and controls current flowing through the first nonlinear element.

For example, a semiconductor device includes one or more first subcontacts electrically conducted to a substrate. At least one of the one or more first subcontacts is formed in an element arrangement region, and has a lower impedance than the substrate. Preferably, at least one of the one or more first subcontacts is adjacent to a circuit element formed in the element arrangement region. Preferably, on the substrate, which is of a first conductivity type, an epilayer of a second conductivity type is formed, and the one or more first subcontacts include a first line having a lower impedance than the substrate, and a semiconductor region of the first conductivity type penetrating through the epilayer to electrically conduct the first line and the substrate to each other.

A power amplifier circuit includes a first transistor having an emitter electrically connected to a common potential, a base to which a first high-frequency signal is input, and a collector from which a third high-frequency signal is output; a second transistor having an emitter electrically connected to the common potential, a base to which a second high-frequency signal is input, and a collector from which a fourth high-frequency signal is output; a first capacitance circuit electrically connected between the collector of the second transistor and the base of the first transistor; and a second capacitance circuit electrically connected between the collector of the first transistor and the base of the second transistor.

Low-noise optical differential receivers are described. Such differential receivers may include a differential amplifier having first and second inputs and first and second outputs, and four photodetectors. A first and a second of such photodetectors are coupled to the first input of the differential amplifier, and a third and a fourth of such photodetectors are coupled to the second input of the differential amplifier. The anode of the first photodetector and the cathode of the second photodetector are coupled to the first input of the differential amplifier. The cathode of the third photodetector and the anode of the fourth photodetector are coupled to the second input of the differential amplifier. The optical receiver may involve two stages of signal subtraction, which may significantly increase noise immunity.

A distributed amplifier includes: a transmission line having an input end that an input signal is input to; a transmission line having an output end that an output signal is output from; an input termination resistor connected to an end terminal of the transmission line; a plurality of unit cells arranged along the transmission lines, and having input terminals connected to the transmission line and output terminals connected to the transmission line; and a variable current source having one end connected to the end terminal of the transmission line and another end connected to a power supply voltage, and capable of adjusting a current amount between the transmission line and the power supply voltage.

Power supplies for electronic devices (e.g. medical imaging devices) are disclosed herein. In one embodiment, a switched mode power supply is minimized in size and weight while maintaining efficiency and an artifact-free image using power supply design techniques tailored to increasing the power conversion frequency to be above the desired receive band of an ultrasound imaging system. In another embodiment, a switched mode power supply is minimized in size and weight while maintaining efficiency and an artifact-free image using power supply design techniques tailored to increasing the power conversion frequency to be just below the desired receive band of an ultrasound imaging system causing the third harmonic and possibly the second harmonic to fall just above the desired receive band.

A circuit includes a main amplifier having a first input and a first output. A main bias circuit is coupled to the main amplifier, and the main bias circuit configured to operate the main amplifier in a first frequency band. A feedforward cancellation amplifier has a second input and a second output, in which the second input is coupled to the first input, and the second output is coupled to the first output. A filter is coupled between the first input and the second input. A feedforward bias circuit is coupled to the feedforward cancellation amplifier. The feedforward bias circuit is configured to operate the feedforward cancellation amplifier in a second frequency band within and narrower than the first frequency band.

An amplifier includes a first differential input pair of transistors having a first input terminal, a second input terminal, a first output terminal, and a second output terminal. A second differential input pair of transistors has a third input terminal, a fourth input terminal, a third output terminal, and a fourth output terminal. The first input terminal is coupled to the third input terminal, the second input terminal is coupled to the fourth input terminal, the first output terminal is coupled to the third output terminal, and the second output terminal is coupled to the fourth output terminal. A cross-over circuit has a control input coupled to the second fourth input terminals. The cross-over circuit is configured to vary an amount of bias current through the second differential input pair of transistors based on a magnitude of a voltage on the second and fourth input terminals.

An operational amplifier 1 comprises transistors Q1 and Q2 forming an input stage, and input resistors R1 and R2 which form a filter together with parasitic capacitors C1 and C2 accompanying the transistors Q1 and Q2. Resistance values R of the resistors R1 and R2 may be set to R=1/(2π.Math.fc.Math.C), where C is the capacitance value of each of the parasitic capacitors C1 and C2, and fc is the target cutoff frequency of the filter. The operational amplifier 1 may also include a power supply resistor R0 which forms a filter together with a parasitic capacitor C0 accompanying a power supply line.