Fully-differential log-domain integrator with orthogonal common-mode and differential-mode responses

In this paper, an all NPN fully-differential log-domain integrator is proposed. The common-mode response of the proposed integrator, unlike those of the previously reported ones, is linear and independent on differential signal. This makes the proposed integrator less susceptible to the variations of the common-mode signal than its predecessors. Simulation results of both differential-mode and common-mode responses are given.