A Novel Method of Echo Suppression Using a Bilateral Optoisolator Circuit

In the telephone network, an echo is generated at the hybrid junction that connects four- to two-wire lines. A conventional echo suppressor or canceller is designed on the assumption that the echo is actually induced. On the contrary, in this novel method using a bilateral optoisolator circuit, the echo is suppressed at its origin. This bilateral optoisolator circuit has not only the property of bilateral transmission, but also the same property of suppression impedance fluctuation as is characteristic of a buffer amplifier. Experimental results show that the degradation of echo return loss can be kept within a few decibels even under the severe condition that the line impedance changes from zero to infinity.