An ECL transistor pair is connected in parallel with a third transistor. A complementary signal is applied to the transistor pair. A high level of a signal that is applied to the third transistor is effectively higher than a high level of the input to the pair of transistors; and a low level of the signal applied to the third transistor is effectively lower than the high level of the input to the pair of transistors. The low level input to the third transistor enables the ECL circuit to output the complementary input signal and assures high speed ECL operation. The high level of the input to the third transistor disables the ECL circuit from outputting the complementary input signal.