An analysis of low-frequency second-order distortion in bipolar transistors applied to an amplifier

A distortion theory for bipolar transistors is applied to reduce low-frequency second-order distortion M/SUB 2/ in an amplifier. An equation for M/SUB 2/ is developed in terms of the physical parameters of the transistor. It is found that M/SUB 2/ depends critically on generator resistance that can be optimized for the transistor studied. The theory and this finding are then applied to the distortion producing Darlington pair in an amplifier, and an optimal value of base resistance for the second transistor is predicted and verified to improve M/SUB 2/ by 30 dB at 5 MHz for the pair. The corresponding improvement in the amplifier is 17 dB (from -50 to -70 dB) at 5 MHz and is accompanied by a small, acceptable degradation in M/SUB 3/ of 3 dB at high frequencies.