Low noise amplifiers (LNAs) with low noise figure are provided. In certain embodiments, an LNA includes a single-ended LNA stage including an input for receiving a single-ended input signal from an antenna and an output for providing a single-ended amplified signal, a balun for converting the single-ended amplified signal to a differential signal, and a variable gain differential amplification stage for amplifying the differential signal from the balun. Implementing the LNA in this manner provides low noise figure, high gain, flexibility in controlling gain, and less sensitivity to ground/supply impedance.

Low noise amplifiers (LNAs) with low noise figure are provided. In certain embodiments, an LNA includes a single-ended LNA stage including an input for receiving a single-ended input signal from an antenna and an output for providing a single-ended amplified signal, a balun for converting the single-ended amplified signal to a differential signal, and a variable gain differential amplification stage for amplifying the differential signal from the balun. Implementing the LNA in this manner provides low noise figure, high gain, flexibility in controlling gain, and less sensitivity to ground/supply impedance.

A power amplifier circuit includes lower-stage and upper-stage differential amplifying pairs, a combiner, first and second inductors, and first and second capacitors. First and second signals are input into the lower-stage differential amplifying pair. The upper-stage differential amplifying pair outputs first and second amplified signals. The combiner combines the first and second amplified signals. The lower-stage differential amplifying pair includes first and second transistors. A supply voltage is supplied to the collectors of the first and second transistors. The first and second signals are supplied to the bases of the first and second transistors. The upper-stage differential amplifying pair includes third and fourth transistors. A supply voltage is supplied to the collectors of the third and fourth transistors. The emitters of the third and fourth transistors are grounded via the first and second inductors and are connected to the first and second transistors via the first and second capacitors.

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.

An amplifier circuit includes an amplifier having an amplifier input and an amplifier output. The amplifier circuit includes a transformer having a primary winding in series with the amplifier output and a secondary winding coupled to the amplifier input. The primary winding and the secondary winding are arranged such that a portion of a magnetic field generated by the primary winding couples to the secondary winding through a magnetically coupled feedback loop, thereby providing feedback from the amplifier output to the amplifier input. An output load arrangement is connected to the primary winding wherein the output arrangement includes a balun. The amplifier circuit may be implemented as an integrated circuit and where the primary and secondary windings are integrated in different metal layers of the integrated circuit or are otherwise arranged to effect a desired degree of magnetic coupling and feedback from the amplifier output to the amplifier input.

An amplifier circuit includes an amplifier having an amplifier input and an amplifier output. A transformer disposed to provide a signal for driving a load includes a primary winding in series with the amplifier output. A secondary winding of the transformer is coupled to the amplifier input where the primary winding and the secondary winding are arranged such that a portion of a magnetic field generated by the primary winding couples to the secondary winding so as to establish a magnetically coupled feedback loop from the amplifier output to the amplifier input. A loop gain of the magnetically coupled feedback loop is substantially independent of an impedance of the load and is defined at least in part by a coupling factor and turn-ratio of the transformer. The load may be included within an output load arrangement including a balun.

A stacked amplifier circuit includes an input stage having first and second input ports respectively defined by inputs of first and second transistors. A transformer arrangement includes first and second primary windings and first and second secondary windings. The first secondary winding is connected to an output of the first input transistor and the second secondary winding is connected to an output of the second input transistor. Portions of the magnetic fields generated by the primary windings couple to their respective secondary windings. An output stage is AC coupled to the first and second secondary windings and has an output connected to the first and second primary windings. The input stage and the output stage are arranged in a stacked configuration such that a bias current of the output stage is reused as bias current for the input stage.

An amplifier circuit including a first amplifier having a first amplifier input and a first amplifier output and a transformer including a first transformer component having a first primary winding in series with the first amplifier output and a first secondary winding coupled to the first amplifier input. The first primary winding and the first secondary winding are arranged such that a portion of a first magnetic field generated by the first primary winding couples to the first secondary winding through a first magnetically coupled feedback loop. The transformer further includes a second transformer component having a second primary winding in series with an output of a second amplifier and a second secondary winding coupled to an input of the second amplifier input. A portion of a second magnetic field generated by the second primary winding couples to the second secondary winding through a second magnetically coupled feedback loop.

An amplifier includes a first coil coupled to at least one input node. The amplifier further includes second and third coils. A first terminal of the second coil is coupled to a source terminal of a first transistor, while a second terminal of the second coil is coupled to a source terminal of a second transistor. A third coil includes first and second terminals coupled to gate terminals of the first and second transistors, respectively. Responsive to receiving an input signal, the first coil electromagnetically conveys the signal to the second and third coils.

Techniques for monitoring a distortion signal of a power amplifier circuit, where the output of a distortion monitoring circuit includes little or no fundamental signal and closely represents the actual distortion of the amplifier circuit of a wired communications system. The power amplifier circuit can generate a distortion feedback signal that does not affect the power amplifier's output power capability, e.g., no inherent loss in the fundamental output of the amplifier. That is, using a distortion monitor circuit, the power amplifier circuit can resolve a distortion feedback signal from the intended output signal of the output power amplifier circuit.