Radio frequency (RF) amplifiers are used in a variety of conventional applications. As an example, RF amplifiers are frequently used in data communications in order to increase the range or signal quality of data signals communicated through a network. Ideally, a RF amplifier is linear such that its output signal varies proportionally to its input signal. However, in reality, the transfer function of all RF amplifiers contains some non-linear terms, and these introduce some harmonic or intermodulation distortion in the output signal. In a narrow-band communication system, second order distortion falls outside the frequency band of interest, and can be removed by filtering. However, filtering is inappropriate where the instantaneous bandwidth is greater than an octave such that the second order harmonics or intermodulation products fall in band.
One solution that has been used to reduce second order harmonic distortion in wideband systems involves the use of multiple amplifiers arranged in a parallel, balanced or anti-phase configuration such that asymmetrical distortion in each amplifier produces symmetrical distortion in the output signal, thereby cancelling the effects of second order harmonics. However, the use of a parallel path for amplifiers is not always possible or convenient, and techniques for reducing second order distortion in the output of an amplifier without requiring an additional amplifier in a parallel, anti-phase arrangement are generally desired.
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