A two-stage amplifier of a type of the current re-use configuration is disclosed. The amplifier includes first to third transistors, where the first transistor constitute the first stage, while, the latter two transistors constitute the second stance. The first to third transistors are connected in series between a power supply and ground such that a bias current supplied to the third transistor flows in the second and first transistors. The first transistor in the source thereof is grounded in the DC mode. The second transistor is grounded in the AC mode but floated in the DC mode. The third transistor that outputs an amplified signal is connected in parallel in the AC mode but in series in the DC mode with respect to the second transistor.

An excessive voltage rise of load voltage, caused by an impedance mismatching on a transmission path, is prevented, and high-frequency power is regenerated. A parallel impedance is connected to the transmission path during the voltage rise, thereby regenerating voltage caused by a standing wave and preventing excessive load voltage, together with enhancing energy usage efficiency. Establishing the parallel impedance for the load impedance, on the transmission path between the high-frequency amplifier circuit of the high-frequency power supply device and the high-frequency load, reduces impedance at the connecting position to prevent generation of excessive voltage on the transmission path, and high-frequency power is regenerated from the transmission path by the parallel impedance.

Apparatus and methods for an inverted Doherty amplifier operating at gigahertz frequencies are described. RF fractional bandwidth and signal bandwidth may be increased over a conventional Doherty amplifier configuration when impedance-matching components and an impedance inverter in an output network of the inverted Doherty amplifier are designed based on characteristics of the main and peaking amplifier and asymmetry factor of the amplifier.

Provided is a high-frequency amplifier capable of making a circuit substrate small and reducing a cost. A high-frequency amplifier is provided with a first substrate including a matching unit, and a second substrate including a transistor and a first impedance converter connected to each other, in which the matching unit of the first substrate and the first impedance converter are connected to each other via a first connection. Furthermore, the high-frequency amplifier is further provided with a third substrate including a matching unit, in which the second substrate may further include a second impedance converter connected to the transistor, and the second impedance converter and the matching unit of the third substrate may be connected to each other via a second connection.

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.

A circuit including an amplifier having an input and an output; and a feedback path comprising a transmission line electrically coupled or electrically connected to the output and the input. A low noise amplifier including the circuit wherein the feedback path cancels noise generated in the low noise amplifier.

A harmonic processing circuit includes: a feeder line configured to feed power to an amplifying device; and a harmonic processing unit connected to the feeder line, and configured to perform harmonic processing to a harmonic of a signal outputted from the amplifying device. The feeder line is connected to a fundamental wave matching circuit that is connected to the amplifying device and performs matching with respect to a fundamental wave of the signal.

A balun is disclosed and includes a dielectric substrate defining a first surface and a second surface. The balun includes a first output port including a first output ground portion and first output power portion; a second output port including a second output ground portion and a second output power portion; and an input port including an input ground portion and input power portion. The first output ground portion, the second output ground portion, and the input ground portion are coupled at a ground junction portion. The first output power portion, the second output power portion, and the input power portion are coupled at a power junction portion. The first output power portion, the second output power portion, and the input power portion are positioned on the first surface. The first output ground portion, the second output ground portion, and the input ground portion are positioned on the second surface.

Example embodiments relate to push-pull class E amplifiers. One example push-pull class E amplifier includes an input configured for receiving a signal to be amplified. The push-pull class E amplifier also includes an output configured for outputting the signal after amplification. Additionally, the push-pull class E amplifier includes a printed circuit board having a first dielectric layer and a second dielectric layer. Further, the push-pull class E amplifier includes a first amplifying unit and a second amplifying unit. Yet further, the push-pull class E amplifier includes a balun, a capacitive unit, a first line segment, a second line segment, a third line segment, and a fourth line segment. The first line segment and the second line segment are arranged on the first dielectric layer. A combined length of the third line segment and the fourth line segment corresponds to a quarter wavelength of an operational frequency of the amplifier.

Systems and methods for a tunable impedance are provided. A tunable impedance includes a transistor assembly having two terminals and a control input. The transistor assembly includes one or more transistors electrically connected between the two terminals to provide a first impedance between the two terminals, based upon a control signal. One or more replica transistors react to the control signal in a similar fashion as the transistor assembly, to provide a replica impedance based upon the control signal. A control circuit is configured to generate the control signal based upon a voltage across the replica transistor(s) and/or a current through the replica transistor(s).