A bio-impedance measurement circuit with a high speed automatic driving current signal (carrier) cancellation technique is proposed. In the previous work, the carrier cancellation method was presented, and in this paper an automatic version is proposed. Automatic processing time is important in electrical impedance tomography applications for fast image generation rate, because the measurement time increases in proportion to the number of electrode combinations. The designed circuit was implemented using CMOS 180-nm process technology. The processing time of the newly proposed automatic carrier cancellation technique was measured to be 7ms, which is about 1000 times better than the previous one.