	US 12,149,210 B2
	Amplifier linearization using magnetically coupled feedback
Ali Fard, Corona Del Mar, CA (US); and Mats Carlsson, Sundbyberg (SE)
Assigned to QuantalRF AG, (CH)
Filed by QuantalRF AG, Zurich (CH)
Filed on Sep. 27, 2021, as Appl. No. 17/486,339.
Claims priority of provisional application 63/084,497, filed on Sep. 28, 2020.
Prior Publication US 2022/0103132 A1, Mar. 31, 2022
Int. Cl. H03F 3/26 (2006.01); H01F 38/14 (2006.01); H03F 1/16 (2006.01); H03F 1/32 (2006.01); H03F 1/34 (2006.01); H03F 3/21 (2006.01); H03F 3/24 (2006.01)

CPC H03F 1/32 (2013.01) [H01F 38/14 (2013.01); H03F 1/3229 (2013.01); H03F 1/3247 (2013.01); H03F 1/347 (2013.01); H03F 3/21 (2013.01); H03F 3/24 (2013.01); H03F 2200/09 (2013.01); H03F 2200/451 (2013.01); H03F 2200/534 (2013.01); H03F 2200/541 (2013.01)]

24 Claims

1. An amplifier circuit, comprising:

an amplifier having an amplifier input and an amplifier output;

a transformer having a primary winding in series with the amplifier output and a secondary winding coupled to the amplifier input wherein 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, the transformer providing a current or voltage for driving a load included within an output load arrangement connected to the primary winding of the transformer;

wherein 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;

wherein an inductance (L₂) of the secondary winding is selected in conjunction with a parasitic capacitance (C_g) between the amplifier input and ground such that resonance of the amplifier circuit occurs at a resonant frequency (f₀) equivalent to a desired frequency of operation wherein f₀is represented as: