A radio frequency amplifier comprises a transistor, a transformer and a variable capacitor. The transistor has an input terminal, an output terminal and a control terminal. The transformer has a first coil conductor and a second coil conductor. The first coil conductor magnetically couples to the second coil conductor. The second coil conductor connects to the control terminal. The first coil conductor connects to the input terminal. The variable capacitor connects in parallel with the second coil conductor. The radio frequency amplifier is configured to be an input or output stage of an integrated circuit. An integrated circuit using the radio frequency amplifier is also introduced.

Front end systems and related devices, integrated circuits, modules, and methods are disclosed. One such front end system includes a low noise amplifier in a receive path and a multi-mode power amplifier circuit in a transmit path. The low noise amplifier includes a first inductor, an amplification circuit, and a second inductor magnetically coupled to the first inductor to provide negative feedback to linearize the low noise amplifier. The multi-mode power amplifier circuit includes a stacked output stage including a transistor stack of two or more transistors. The multi-mode power amplifier circuit also includes a bias circuit configured to control a bias of at least one transistor of the transistor stack based on a mode of the multi-mode power amplifier circuit. Other embodiments of front end systems are disclosed, along with related devices, integrated circuits, modules, methods, and components thereof.

A low noise amplifier includes an amplifier transistor having a source, a gate, and a drain. An input node is coupled to the gate. An output node is coupled to the drain. An inductor is coupled between the gate and the drain.

A radio frequency low noise amplifier circuit with a receive signal input, a receive signal output, and a voltage source include a low noise amplifier and a coupled inductor circuit with a primary inductive chain connected to the output of the low noise amplifier and to the voltage source. The coupled inductor circuit further includes a secondary inductive chain with a first inductor electromagnetically coupled to the primary inductive chain, and a second inductor in series with the first inductor and magnetically coupled to the primary inductive chain. The second inductor is connected to a feedback node of the low noise amplifier. There is an output matching network connected to the first inductor of the secondary inductive chain and to the receive signal output.

Design of ultra broadband transimpedance amplifiers (TIA) for optical fiber communications is disclosed. In one embodiment, a TIA comprises a g.sub.m-boosted dual-feedback common-base stage, a level shifter and an RC-degenerated common-emitter stage, and a first emitter-follower stage, wherein the first emitter follower stage is inductively degenerated. An output of the TIA is buffered using a second emitter-follower stage.

A method of operating an amplifier circuit having a transformer arranged so as to establish a magnetically coupled feedback loop between and output of an amplifier and an input of the amplifier. The method includes providing a DC bias current to the amplifier, and further includes increasing the DC bias current to improve a linearity of the amplifier circuit wherein a transfer gain of the amplifier circuit remains constant when the DC bias current is increased. A loop gain of the magnetically coupled feedback loop is set by selecting a coupling factor and turn-ratio of the transformer.

Aspects of this disclosure relate to an impedance transformation circuit for use in an amplifier, such as a low noise amplifier. The impedance transformation circuit includes a matching circuit including a first inductor. The impedance transformation circuit also includes a second inductor. The first and second inductors are magnetically coupled to each other to provide negative feedback to linearize the amplifier.

An amplifier for signal amplification, the amplifier comprising: a signal input arrangement; a signal output arrangement; a first transistor (Q.sub.1); a second transistor (Q.sub.2); and a third transistor (Q.sub.3), wherein: the first (Q.sub.1), second (Q.sub.2) and third (Q.sub.3) transistors are coupled to one another to form a transconductance cell, the transconductance cell is coupled to the signal input arrangement and the signal output arrangement, and the transconductance cell is operable to receive a first signal from the signal input arrangement, amplify the first signal and output an amplified first signal to the signal output arrangement. There is also disclosed a receiver incorporating the amplifier and methods of operating the amplifier.

Aspects of this disclosure relate to an impedance transformation circuit and overload protection for a low noise amplifier. A low noise amplifier can include a first inductor, an amplification circuit configured to amplify a radio frequency signal, and a second inductor magnetically coupled to the first inductor to provide negative feedback to linearize the low noise amplifier. A switch can be coupled to the amplification circuit of the low noise amplifier. An overload protection circuit can adjust an impedance of the switch based on a signal level associated with the radio frequency signal to provide overload protection for the low noise amplifier.

A power amplification circuit includes a first transistor, which includes a source coupled to a first power supply and receives an input signal at a gate of the first transistor, a capacitor, which includes a first terminal and a second terminal, the first terminal being coupled to a drain of the first transistor, and a transformer, which is coupled between the second terminal and the gate of the first transistor, transforms a first signal input from the second terminal, and outputs a second signal having a phase different from a phase of the first signal to the gate of the first transistor. The first transistor outputs an output signal from the drain of the first transistor.