Abstract: An amplifier circuit (300, 400, 500) employs negative feedback and a method (600) for providing such feedback to reduce distortion and/or an output impedance of the amplifier circuit, without adversely impacting the overall stability of the amplifier circuit. The amplifier circuit includes a forward path and a feedback path. The forward path includes at least one amplifier (301, 305) arranged in series with an output lowpass filter (307). The amplifier receives a feedback-compensated input signal and amplifies the input signal to produce an amplified signal. The feedback path includes a lowpass filter (311), a highpass filter (313), and a summing arrangement (315) that selectively include and exclude the output lowpass filter from the feedback loop. The feedback lowpass filter is operably coupled to an output of the output lowpass filter and attenuates high frequency components of the amplifier circuit's output signal to produce a lowpass-filtered feedback signal.

Abstract: A circuit (200) includes a four-terminal voltage controlled voltage source (VCVS, 201) coupled to a three-terminal amplifying device (203), whereby when an input signal is applied to a negative input terminal (205) of the VCVS (201), the circuit (200) operates in a manner substantially complementary to the amplifying device (203). Such a circuit (200) may be considered a “virtual” three-terminal amplifying device and may be beneficially coupled in a complementary manner with another three-terminal amplifying device that is substantially identical to the three-terminal amplifying device (203) included in the circuit (200) to form a composite amplifier circuit (e.g., 407) that achieves intended performance over varying operating conditions.