Active termination circuit for low power, low cost BMIC communication link

Abstract

This thesis presents a design of a low cost and low power BMIC communication interface termination circuit. The circuit is designed to overcome the limitations of passive termination methods in terms of galvanic isolation and electromagnetic interference (EMI). In Chapter 2, the communication line termination methods are studied in terms of signal integrity and EMI susceptibility. In Chapter 3, an active termination methodology is proposed as a solution to overcome the limitations of passive termination methods. The proposed active termination circuit uses a Gm block with its driving source follower circuit to terminate the common-mode with a low impedance, while keeping the differential-mode termination impedance high. To enhance the output impedance of the Gm block in strong EMI termination situations, a source-side current sensing feedback loop is proposed as a area-efficient impedance boosting solution. The proposed active termination circuit was implemented in DB HiTek 0.18 um BCD process. The prototype circuit is designed to operate with 5 V supply voltage, and shows 1.4 mA bias current consumption. The measurement results show that the common-mode voltage is less than 3 V, and differential-mode signal transmission efficiency is more than 0.64 under 1 W and 0.5 W level of EMI, for each. The proposed active termination circuit provides a low cost and low power solution for BMIC communication interface circuits by overcoming the limitations of passive termination methods in terms of galvanic isolation and EMI susceptibility.