A method for improving or eliminating second harmonic and higher even order distortion terms and balance of fundamental signals in push-pull amplifiers and other differential circuits is disclosed. A common-mode (CM) signal is generated as a sum of two complementary (out of phase) signals in a summation network. The CM signal contains even order distortion terms only, while the fundamental signal and odd order distortion terms are canceled, thus providing a correction signal that can be used to reduce even order distortion terms, by injecting the correction signal with proper phase and amplitude, into suitable circuit nodes. For feedback, the correction signal is injected at the input of the amplifiers, for feed-forward, it's injected at the output. The correction signal can be amplified to higher levels and injected into the circuit, without affecting gain of fundamental signals; and can result in significant even order distortion improvements, and improved balance of complementary fundamental signals.