Analytical expressions for maximum operating frequencies of emitter-coupled logic and source-coupled FET logic toggle flip-flops

This paper proposes an analytical expression for the maximum operating frequency of an emitter-coupled-logic master-slave toggle flip-flop (ECL MS TFF) based on an impulse response method. The analytical expression was in good agreement with not only SPICE simulations, but also experimental values. The analytical expression also indicated that state-of-the-art InP-based heterojunction bipolar transistors have potential to achieve over 100-GHz operation in ECL MS TFFs. Also, the proposed method was applied to the maximum operating frequency of a source-coupled FET logic (SCFL) MS TFF.