System and method for adjusting amplifier bias current based on input signal envelope tracking

A method, comprising:

• receiving an input signal having an envelope;
• generating an envelope detection signal corresponding to the envelope of the input signal;
• adjusting a bias current provided to an amplifier circuit based upon the envelope detection signal, the amplifier circuit including an amplifier and a transformer, the transformer being configured to establish a magnetically coupled feedback loop from an output of the amplifier to an input of the amplifier wherein the transformer has a primary winding in series with the output of the amplifier and a secondary winding coupled to the input of the amplifier 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 the magnetically coupled feedback loop;
• providing, by the amplifier circuit, an output signal in response to the input signal;
• providing, by the secondary winding, the output signal to a load arrangement including a balun;
• wherein an inductance (L2) of the secondary winding is selected in conjunction with a parasitic capacitance (Cg) between the input of the amplifier circuit and ground such that resonance occurs at a resonant frequency (f0) equivalent to a desired frequency of operation.

A system, comprising:

• an envelope detector configured to generate an envelope detection signal corresponding to an envelope of an input signal;
• and
• an amplifier circuit coupled to the envelope detector and configured to provide an output signal in response to the input signal, the amplifier circuit including an amplifier and a transformer coupled to a load arrangement, the transformer being connected to an output of the amplifier and being configured to establish a magnetically coupled feedback loop from an output of the amplifier to an input of the amplifier wherein the transformer has a primary winding in series with the output of the amplifier and a secondary winding coupled to the input of the amplifier 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 the magnetically coupled feedback loop and wherein a loop gain of the magnetically coupled feedback loop is substantially independent of an impedance of a load included within the load arrangement and is defined at least in part by a coupling factor and turn-ratio of the transformer;
• wherein a bias current, and not a supply voltage, provided to the amplifier circuit is adjusted based upon the envelope detection signal.

A system, comprising:

• an envelope detector configured to generate an envelope detection signal corresponding to an envelope of an input signal;
• an amplifier circuit coupled to the envelope detector and configured to provide an output signal in response to the input signal, the amplifier circuit including an amplifier and a transformer, the transformer being configured to establish a magnetically coupled feedback loop from an output of the amplifier to an input of the amplifier wherein the transformer has a primary winding in series with the output of the amplifier and a secondary winding coupled to the input of the amplifier 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 the magnetically coupled feedback loop,
• a load arrangement coupled to the primary winding;
• and
• wherein a bias current provided to the amplifier circuit is adjusted based upon the envelope detection signal and wherein an inductance (L2) of the secondary winding is selected in conjunction with a parasitic capacitance (Cg) between the input of the amplifier and ground such that resonance occurs at a resonant frequency (f0) equivalent to a desired frequency of operation.