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).

A variable gain amplifier (VGA) is provided. The VGA includes at least one amplifier circuit, at least one current-steering circuit and at least one bias voltage circuit. Each current-steering circuit is coupled to its corresponding amplifier circuit. Each bias voltage circuit is coupled to its corresponding current-steering circuit to provide a positive bias voltage to each current-steering circuit.

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.

A plurality of transmission lines (3b,3c) are connected to a transistor (1) and have different characteristic impedances. A plurality of open stubs (4a,4b) are connected to the plurality of transmission lines (3b,3c) respectively. A length of each open stub (4a,4b) is shorter than a length of each transmission line (3b,3c).

A radio frequency power amplifier and a device are disclosed. A first microstrip line and a second microstrip line are coupled, one end of the second microstrip line is an open stub and another end of the second microstrip line is grounded; and the first microstrip line having a first width is connected to a first transmission line having a second width which is wider than the first width. Therefore, some harmonic bands suppression can be implemented independently. Furthermore, the harmonic termination is independent and may not impact one or more fundamental components during matching a network. In addition, it may not take up more space and is sufficiently compact. Furthermore, sufficient wide harmonic response bandwidth can be provided.

An multistage amplifier includes first to third FETs, a drain of the second FET is connected to a gate of the third FET in an AC manner, a source thereof is grounded in a DC manner, a drain of the first FET is connected to a gate of the second FET in an AC manner, a source thereof is grounded in a DC manner, a gate thereof receives a high frequency signal, a drain of the third FET receives a bias current and outputs an amplified signal, a source thereof is grounded in an AC manner, the drains of the first and second FETs are connected to the source of the third FET in a DC manner via a transmission line having an electrical length of /4 when a wavelength of the high frequency signal is , and a size of third FET is greater than other FETs.

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 gain adjustment unit constituted by a distribution switch having a control terminal is provided in an input unit of an amplifier circuit. One end of a coupler is connected to an output line of the amplifier circuit, another end of the coupler is connected to an anode of a diode, and a monitor terminal is connected via a low-pass filter to a cathode of the diode. The anode of the diode is unbiased.

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.

A stub whose end is connected to an end of a transmission line, and a coupled line disposed in parallel with each of the transmission line and the stub, and electromagnetically coupled to each of the transmission line and the stub are included, and the stub and the coupled line operate as a first resonator for resonating with an odd order harmonic included in the amplified signal, and the transmission line, the stub, and the coupled line operate as a second resonator for resonating with an even order harmonic included in the amplified signal.