A detailed study on the non-quasi-state (NQS) effects in advanced high-speed bipolar circuits is presented. An NQS Gummel-Poon-compatible lumped circuit model, which accounts for carrier propagation delays across various quasi-neutral regions in bipolar devices, is implemented in the ASTAP circuit simulator. The effects are then evaluated and compared with those for the conventional Gummel-Poon model for the emitter-coupled logic (ECL) circuit, the non-threshold-logic (NTL) circuit, and various advanced circuits utilizing active-pull-down schemes. For the ECL circuit, the effect decreases with reduced power level and increased loading. For the NTL circuit, due to its front-end configuration, the effect is more significant than that for the ECL circuit but tends to increase with reduced power level. As the passive resistors (and the associated parasitic RC effect) are decoupled from the delay path and the circuit delay is made more intimately related to the intrinsic speed of the devices in various advanced active-pull-down circuits, the delay degradation due to NQS effect becomes more significant.
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