Apparatus and methods for power amplifiers isolated by differential ground are provided. In certain implementations, a mobile device includes a transceiver that generates a plurality of radio frequency input signals including a first radio frequency input signal and a second radio frequency input signal, and a plurality of differential power amplifiers including a first differential power amplifier that provides amplification to the first radio frequency input signal and a second differential power amplifier that provides amplification to the second radio frequency input signal. The first differential power amplifier and the second differential power amplifier each operate with differential ground so as to provide isolation between the first differential power amplifier and the second differential power amplifier.

A radio frequency integrated circuit includes an amplification circuit for outputting a radio frequency signal to an antenna, a balun including a first terminal, a second terminal, a third terminal, and a fourth terminal, and a variable capacitance circuit including a fifth terminal and a sixth terminal. The first terminal and the second terminal of the balun receive output signals of the amplification circuit. The third terminal and the fourth terminal of the balun are connected to the fifth terminal and the sixth terminal of the variable capacitance circuit, respectively, and the fifth terminal is connected to a radio frequency output terminal. The variable capacitance circuit includes a plurality of capacity cells that are connected in parallel between two output terminals.

Apparatus and methods for performing wireless communications are provided. In some embodiments, an apparatus includes a transformer including a first winding, a second winding, and a third winding. The apparatus also includes a first transmitter circuit coupled with the first winding, and a second circuit coupled with the second winding. The third winding is coupled with an antenna. The first transmitter circuit is configured to transmit a first signal to the antenna via magnetic coupling between the first winding and the third winding. The second circuit is configured to tolerate without damage a second signal from the first transmitter circuit, wherein the second signal is generated from the first signal via magnetic coupling between the first winding and the second winding. A turn ratio between the first winding and the second winding can be configured to limit a voltage of the second signal to be within a pre-determined threshold.

A power amplifier cell comprising a first power amplifier, a second power amplifier and a balun. The balun comprises a first inductor and a second inductor that define a first transformer; and a third inductor and a fourth inductor that define a second transformer. The following: (i) a parasitic capacitance of the first power amplifier; (ii) a leakage inductance of the first transformer; and (iii) a capacitive coupling between the first inductor and the second inductor, contribute to a first impedance matching circuit for the first power amplifier. Also, the following (iv) a parasitic capacitance of the second power amplifier; (v) a leakage inductance of the second transformer; and (vi) a capacitive coupling between the third inductor and the fourth inductor, contribute to a second impedance matching circuit for the second power amplifier.

An amplification system includes a differential output circuit that provides an amplified output to drive a load. A main amplifier is coupled to a terminal of the differential output circuit via a main path, corresponding to a transmission line. A peak amplifier is coupled to another terminal of the differential output circuit via a peak path, corresponding to a transmission line. In a single-ended mode while the peak amplifier is deactivated for amplification purposes, the peak path performs an impedance inversion to effectively ground the other terminal of the differential output circuit. In a differential mode, each of the peak amplifier and the main amplifier operates to conduct current to respective terminals of the differential output circuit and each of the main path and the peak path provides a predetermined output impedance to the differential output circuit.

Techniques for monitoring a distortion signal of a power amplifier circuit, where the output of a distortion monitoring circuit includes little or no fundamental signal and closely represents the actual distortion of the amplifier circuit of a wired communications system. The power amplifier circuit can generate a distortion feedback signal that does not affect the power amplifier's output power capability, e.g., no inherent loss in the fundamental output of the amplifier. That is, using a distortion monitor circuit, the power amplifier circuit can resolve a distortion feedback signal from the intended output signal of the output power amplifier circuit.

An amplifier system includes a main amplifier, a cross-over current detector and a controller. The main amplifier includes at least a first driving transistor and a second driving transistor serving as a differential pair, wherein the first driving transistor and the second driving transistor are arranged to receive a first input signal and a second input signal, respectively. The cross-over current detector is coupled to the main amplifier, and is arranged for detecting a cross-over current of the main amplifier, wherein the cross-over current of the main amplifier is an overlapped current from the differential pair. The controller is coupled to the main amplifier and the cross-over current detector, and is arranged for generating a control signal to control a gain of the main amplifier according to an output of the main amplifier and the cross-over current of the main amplifier.

A power amplifier device for a magnetic resonance device includes a circuit board with at least one power amplifier module, and at least one electronics structure including coupled conductor paths arranged on opposing sides of the circuit board. The power amplifier device also includes a cooling plate operable for cooling components on the circuit board that heat up during operation and abutting the circuit board on one side. The cooling plate has a depression that follows the course of the conductor path and faces the conductor path in the region of the conductor path of the electronics structure that is arranged on the side of the circuit board facing the cooling plate.

A complementary metal oxide silicon transceiver having an integrated power amplifier is provided. The complementary metal oxide silicon transceiver having the integrated power amplifier is capable of controlling an output power according to a communication environment to solve the following problem that with the increment of an output level of a power amplifier, performance is decreased when noises flow into other blocks of a transceiver with power and thus are inputted to the power amplifier.

A transmitter device which transmits a first transmit signal and a second transmit signal having different wireless communication standards. The transmitter device includes a power amplifier that amplifies the first transmit signal in a first transmission mode. A first impedance circuit provides the amplified first transmit signal to a radio frequency output port. A second impedance circuit is connected to the first impedance circuit and provides an additional impedance to the first impedance circuit in the first transmission mode. A first switch provides the second transmit signal to the first impedance circuit in a second transmission mode. A second switch connects the second impedance circuit and a ground in the first transmission mode, and floats the second impedance circuit in the second transmission mode