An amplifier includes two input terminals to receive a differential, two-tone transmission signal; two output terminals; a coil having terminals connected with the input terminals respectively, and a center tap; a first transistor having the gate connected with one terminal of the coil, and the output terminal connected with one output terminal; a second transistor having the gate connected with the other terminal of the coil, and the output terminal connected with the other output terminal; a diode having a terminal connected with the center tap; and a bias circuit connected with the other terminal of the diode to output a gate voltage to turn on the first and second transistors. The diode adjusts the terminal voltage depending on a signal level of a double harmonic wave of the transmission signal supplied to the terminal of the diode from the center tap.

Embodiments of an RF amplifier include a transistor with a control terminal and first and second current carrying terminals, and a shunt circuit coupled between the first current carrying terminal and a ground reference node. The shunt circuit includes a first shunt inductance, a second shunt inductance, and a shunt capacitor coupled in series. The second shunt inductance and the shunt capacitor form a series resonant circuit in proximity to a center operating frequency of the amplifier, and an RF cold point node is present between the first and second shunt inductances. The RF amplifier also includes a video bandwidth circuit coupled between the RF cold point node and the ground reference node.

An amplifier operates to provide a high output impedance at an output through a push stage having a first transistor of a first transistor type and a pull stage having a second transistor of a second transistor type that is different from the first transistor type. The first transistor and the second transistor are coupled in a common-gate configuration. The first transistor and the second transistor are shorted together via a capacitor coupled to an input and share a common current path as a push-pull current-reusing common-gate low noise amplifier with a broadband input matching.

A mobile device can have a transceiver configured to generate a radio frequency signal and a power management system with envelope tracking. The device can also have a power amplifier system having a driver transistor coupled to a radio frequency signal input, a transformer balun having a main primary coil connected between the driver transistor and a voltage supply node of the power amplifier system, a secondary coil magnetically coupled to the main primary coil and an additional primary coil configured to generate a feedback signal related to a signal of the main primary coil. The power amplifier system can also have a push-pull amplifier with a first transistor having a base connected to a first end of the secondary coil and a second transistor having a base connected to a second end of the secondary coil. Accordingly, push-pull stage neutralization can deploy two transistors cross-connected to opposite ends of an output coil in a transformer balun.

A power amplifier system for amplifying a radio frequency signal can have a driver transistor coupled to a radio frequency signal input. The system can also have a transformer balun with a main primary coil connected between the driver transistor and a voltage supply node of the power amplifier system, a secondary coil magnetically coupled to the main primary coil, and an additional primary coil configured to generate a feedback signal related to a signal induced in the main primary coil. A neutralization diode can be configured to use the feedback signal to reduce a gain variation resulting from variations in a voltage supplied from the voltage supply node of the power amplifier system. The neutralization diode can be connected between the additional primary coil and the driver transistor. Through envelope tracking, voltage supplied through the voltage supply node can change in relation to an envelope of the radio frequency signal.

A LNA comprises an input, a transformer structure and a first transistor and a second transistor, each having with gate, source, and drain terminals. The transformer structure has a first winding pair, a second winding pair and a third winding pair. Each winding of the first winding pair connects to the input node and one source terminals of the transistors. The second winding pair is proximate the first winding pair. The second winding pair connects to a ground node and the transistor source terminals. The third winding pair is proximate the first winding pair and it connects to a bias signal source and a gate terminal of the transistors. An output connects to the transistor drain terminals. The winds of the first and second winding pairs are off set and rotated 180 degrees with respect to the other winding in the pair. The third winding performs a Gm boost function.