Analog functional simulator for multilevel systems

Gate-level simulation of digital circuits using multi-valued Boolean algebras

“…However, because the various Boolean operations are supposed to model the behavior of physical gates, additional constraints must be taken into account: for instance, it seems reasonable to require that the output of an AND gate be equal to the lowest input level (i.e. the AND Boolean operation must behave like the min operator on the input signals [1]). Similarly, the OR operation should yield the max of the inputs.…”

“…The delay model implemented in this algorithm is taken from [1]: it calculates both a delay time for inputs to propagate to the output and a slope value for the output. To take into account the gain of a gate, the output slope s o is expressed as a gate-specific function f o () of the input slope s i and the capacitance at the gate's output, C o :…”

“…Extensive literature exists on this topic: for a detailed bibliography the interested reader is referred to [1,2] and to the references listed therein. A feature common to all published mixed-mode simulation algorithms is that they must trade-off speed versus accuracy, in particular when it comes to simulating the digital portion of a circuit.…”

“…However, the simulation is still performed at the device level using ordinary device models, so that the computational effort required is still substantially greater than gate-level logic simulation [2]. A different approach is given in [1], where a functional-level mixed-mode simulator is described. As in ELOGIC simulation, an arbitrary number of voltage levels between a logic zero and a logic one is available to represent signal values.…”

“…These logic levels provide more information about a waveform than the traditional states (0, 1, X, Z), so slopes of waveforms can be determined and accurate times can be calculated for threshold crossings. There are however a number of differences between the algorithm described here and the one proposed in [1]: one is that our implementation requires only ordinary Boolean algebra operations (except for computing delays). As a consequence of this fact, it is possible to determine the initial state of the circuit by solving a set of Boolean algebraic equations, so that a valid operating point for the circuit can be determined before a transient analysis begins, thus eliminating the need for an unknown state.…”