Linearization of BJTs with Logarithmic Predistortion

This paper proposes a novel linearization technique for bipolar junction transistors (BJT) and their derivatives, e.g., heterojunction BJTs. Since the non-linearity of BJTs is exponential by nature, analog predistortion caused by a logarithmic amplifier should linearize the response completely, in theory. This paper reports that, in practice, cascading a logarithmic amplifier in front of a simple one-transistor BJT amplifier boosted its output third-order inter-modulation intercept point (OIP3) by 10 dB. The proposed linearization scheme is extremely simple and it is inherently broadbanded. To the best of our knowledge, this idea has not been reported previously.