Amplifier linearization using magnetically coupled feedback

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 signal 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 the output load arrangement includes a balun connected to the primary winding and wherein the primary winding provides a first output current to the balun and the balun converts the first output current provided by the primary winding into a second output current;
• wherein the amplifier circuit is characterized by a current gain Ai of:
• A
• i
• =
• i
• o
• i
• s
• =
• A
• i
• ⁢
• ∞
• ⁢
• A
• ⁢
• β
• 1
• -
• A
• ⁢
• β
• where ts is the current provided to the amplifier input, to is the current provided to the output load arrangement, and Aβ is a loop gain defined by:
• A
• ⁢
• β
• =
• -
• g
• m
• ⁢
• R
• p
• ⁢
• k
• n
• where here gm is the transconductance of the amplifier, k is a coupling factor between the primary winding and the secondary winding, Rp is a resistance to ground at the amplifier input, where At∞ is the current gain with infinite loop gain and is expressed as:
• A
• i
• ⁢
• ∞
• =
• n
• k
• where n is a turn-ratio of the transformer, which can be expressed as:
• n
• =
• L
• 2
• L
• 1
• and where L1 is an inductance of the primary winding and L2 is an inductance of the secondary winding.

An amplifier circuit, comprising:

• an amplifier having an amplifier input and an amplifier output;
• a transformer configured to provide feedback from the amplifier output to the amplifier input over a magnetically coupled feedback loop, the transformer having a primary winding connected to the amplifier output and a secondary winding coupled to the amplifier input;
• wherein the transformer provides a current or voltage for driving a load included within an output load arrangement connected to the transformer and wherein a loop gain of the magnetically coupled feedback loop is 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 (Cg) 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 f0 is represented as:
• f
• 0
• =
• 1
• 2
• ⁢
• π
• ⁢
• L
• 2
• ⁢
• C
• g
• .