Compensation of non-idealities in log-domain filters implemented using E cells with NPN transistors

The performance of log-domain circuits is quite degraded due to effects of BJT transistor non-idealities. These include the parasitic emitter and base resistances, and finite beta. A systematic procedure for compensating the effects caused by the above imperfections is presented in this paper. For this purpose, the behavior of the basic nonlinear transconductor building blocks, which are implemented using only NPN bipolar transistors, was studied. The validity of the presented procedure was evaluated through simulation results in case of a lowpass filter.