Showing papers on "NQS published in 1991"

A charge conserving non-quasi-state (NQS) MOSFET model for SPICE transient analysis

Abstract: An analytic charge-conserving non-quasi-static (NQS) model is derived for long-channel MOSFETs and has been implemented in SPICE3. The model is based on approximate solutions to the transient current continuity equation, an analytic equations are derived for node charges using the charge-sheet formulation. The NQS effects in several test circuits, which include a pass transistor, a CMOS inverter chain, and a differential sample-hold circuit, are stimulated. Excellent agreements have been observed among this work, PISCES (2-D device simulation), the 1-D numerical simulation, the multiple lump model, and CODECS (a mixed device and circuit simulation). However, large differences have been observed between this work and conventional quasi-static (QS) models. The model computation time of this work implemented in SPICE3 is about 2-3 times larger than those of QS models (BSIM, Level-2 Meyer) in SPICE3. >

MOS output circuit

Abstract: An output circuit for a memory device has four MOS transistors. A first MOS transistor and a second MOS transistor comprise an output stage of the output circuit, and a control circuit controls the voltages of the gates of the first and the second MOS transistors. A third MOS transistor has its source connected to the gate of the second MOS transistor, and a fourth MOS transistor has its source connected to the gate of the first MOS transistor. When the data which are supplied to the control circuit are changed, the third or the fourth MOS transistor assists the level shift of the gate of the second and the first MOS transistor at the beginning of the level shift. By continuing the level shift, the third or the fourth MOS transistor is turned off. As a result, the source-gate voltage of the third or the fourth MOS transistor becomes lower than its threshold voltage, so that the switching noise or ground noise is reduced.

The modeling and measurement of lateral bipolar junction transistors

Abstract: A physically based, large-signal model for the lateral p-n-p transistor is developed and compared with DC and transient measurements. The analytical equations for the lateral and vertical parts of the lateral p-n-p are derived. The analytical geometrical factor for the lateral p-n-p transistor is developed to derive a charge-based large-signal model. The partitioned-charge method is used to account for the non-quasi-static effects since the lateral p-n-p transistor has a wide base width. The simulation shows good agreement with the measurement, indicating that the PC method is sufficient for modeling the lateral p-n-p transistor without resorting to complex equations for NQS (non-quasi-static) effects. This simple model can reduce the simulation time quite a lot and help the circuit designer in estimating the effect of the parasitic lateral p-n-p for complex integrated circuit design. >

A non-quasi-static collector model for HBTs

Abstract: A large-signal non-quasi-static (NQS) model of a bipolar transistor collector current generator is discussed. It is generally valid for one-dimensional space charge region transport with moving boundaries. Such a model is necessary for self-consistency near the transit time of the region when the quasi-static approximation fails. The model has been applied to an idealized collector region and results are presented. The large signal modulation of the collector depletion region leads to significant harmonic generation for optimized heterojunction bipolar transistors (HBTs) where the majority of the transit time is in the collector. Fundamental current gain is also seen for some load terminations. >

Simulation and assessment of non-quasi-static current crowding in scaled bipolar circuits

Abstract: A novel method of accounting for non-quasi-static (NQS) effects in a seminumerical bipolar junction transistor (BJT) circuit model, based on the use of the previous time-step solution in the current time-step analysis, is used to simulate and assess transient current crowding is scaled bipolar circuits. The model, supported by numerical device simulations, reveals significant NQS delay, even in circuits comprising submicron BJTs. It is noted that the novel modeling/implementation involving the use of the previous time-step solution to update the model for the current time-step analysis could be a viable means of accounting for general NQS behavior in semi-numerical transient device/circuit simulation. For example, the transient-field (dE/dt) dependence of hot-electron drift velocity in scaled BJTs, which portends a NQS aspect of the velocity overshoot, can be accounted for via the methodology described. >