An on-chip transformer circuit is disclosed. The on-chip transformer circuit comprises a primary winding circuit comprising at least one turn of a primary conductive winding arranged as a first N-sided polygon in a first dielectric layer of a substrate; and a secondary winding circuit comprising at least one turn of a secondary conductive winding arranged as a second N-sided polygon in a second, different, dielectric layer of the substrate. In some embodiments, the primary winding circuit and the secondary winding circuit are arranged to overlap one another at predetermined locations along the primary conductive winding and the secondary conductive winding, wherein the predetermined locations comprise a number of locations less than all locations along the primary conductive winding and the secondary conductive winding.

Optimized impedance characteristics of a variable impedance device causes the apparatus to transmit wireless signals with minimal out-of-band transmission at an optimized efficiency of the power amplifier. The variation of impedance characteristics of an antenna cause a change in the coefficients of a mapping function. The relatively fast variations to the power supply voltage of a power amplifier are applied to the mapping function to generate control signals which vary the impedance characteristics of a variable impedance device. The output of the mapping function includes control signals that control optimized impedance characteristics of a variable impedance device as a function of the variation of the supply voltage to a power amplifier. The coefficients of the mapping function may be regularly determined based on a comparison of out-of-band power and in-band power transmitted by an antenna.

According to one embodiment, a high-frequency amplifier includes an active element and an output matching circuit. The active element is provided on a substrate. The active element is configured to amplify a signal having a frequency band. The active element includes a cell region. The output matching circuit is connected to the active element. The output matching circuit includes a wire, a transmission line and an output terminal. The wire includes an input end and an output end. The input end of the wire is connected to an output part of the cell region of the active element. The transmission line is provided on the substrate. The transmission line includes an input part and an output part. The input part of the transmission line is connected to the output end of the wire. The output terminal is provided on the substrate.

A communication device includes a power amplifier that generates power signals according to one or more operating bands of communication data, with the amplitude being driven and generated in output stages of the power amplifier. The final stage can include an output passive network that suppresses suppress an amplitude modulation-to-phase modulation (AM-PM) distortion. During a back-off power mode a bias of a capacitive unit of the output power network component can be adjusted to minimize an overall capacitance variation. A output passive network can further generate a flat-phase response between dual resonances of operation.

A Doherty amplifier is configured in such a manner that: the ratio Z.sub.3/Z.sub.2 of a characteristic impedance Z.sub.3 of a second transmission line to a characteristic impedance Z.sub.2 of a first transmission line is a power division ratio P.sub.2/P.sub.3 of a signal to be amplified between a carrier amplifier and a peak amplifier when both of the carrier amplifier and the peak amplifier are saturated; and a resistance value R.sub.iso of a resistor is a value obtained by multiplying, by a proportionality coefficient w which is equal to or greater than 0 but less than 1, the sum of the input impedance Z.sub.cin0 of the carrier amplifier when the carrier amplifier reaches saturation and the input impedance Z.sub.pin0 of the peak amplifier when the peak amplifier reaches saturation.

A Doherty amplifier according to the disclosure includes an input terminal, a first input transmission line connected to the input terminal via a branch portion, a second input transmission line connected to the input terminal via the branch portion, a carrier amplifier connected to the first input transmission line, a peak amplifier connected to the second input transmission line, a first output transmission line including one end connected to output of the carrier amplifier, a second output transmission line including one end connected to output of the peak amplifier, a synthesis line including one end connected to another end of the first output transmission line and another end of the second output transmission line and an output terminal connected to another end of the synthesis line, wherein the first output transmission line includes a wide portion which is wider than another portion of the first output transmission line.

An output matching circuit includes: a converter electrically connected to an output end of a power amplifier element to convert an impedance of the output end to an impedance higher than the impedance of the output end by magnetic coupling; and a first filter circuit electrically connected between the output end of the power amplifier element and the converter to make a short circuit in a frequency band different from a predetermined transmission frequency band.

A digital power amplifier comprising at least two individually activatable amplifiers connected to an output network comprising a first hybrid coupler. An output of a first amplifier is connected to a first input of the first hybrid coupler and an output of a second amplifier is connected to a second input of the first hybrid coupler such that activating an amplifier of the at least two amplifiers causes the amplifier to load modulate another activated amplifier of at least two amplifiers.

An amplifier is configured in such a way that a first capacitor resonates at the frequency of a second harmonic wave included in a signal outputted from an amplifying element, a circuit including a second transmission line, the first capacitor, and a second capacitor resonates at the frequency of a third harmonic wave included in the signal outputted from the amplifying element, and also matches the impedance for a fundamental wave together with an impedance matching circuit.

The disclosure relates to a pre-5.sup.th-Generation (5G) or 5G communication system to be provided for supporting higher data rates Beyond 4.sup.th-Generation (4G) communication system such as Long-Term Evolution (LTE). A Doherty power amplifier of a wireless communication system is provided. The Doherty power amplifier includes a first power amplifier, a second power amplifier, a first transmission line, a 4-port coupler, and a load impedance, and the 4-port coupler includes a first port, a second port, a third port, and a fourth port, the first power amplifier is coupled with the 4-port coupler through the first port, the second power amplifier is coupled with the 4-port coupler through the fourth port, the load impedance is coupled with the 4-port coupler through the third port, the first transmission line is disposed between the first power amplifier and the first port of the 4-port coupler, and the second port is an output end of the power amplifier.