Circuit-level simulators : Circuit-level simulators   are used to model the behaviour of a circuit at its lowest conceptual level. The circuit is described in terms of transistors, wires, capacitors and resistors and their respective interconnectivity. Circuit-level simulators manipulate extensive detail regarding the interaction of all the components in the circuit and also take into consideration subtleties such as wire resistance and geometric properties of the subcomponents.
The end goal circuit level simulation is to produce very detailed analog waveforms which accurately model the behaviour of the circuit's devices in the real world. Consequently, continuous simulation techniques are often used to implement circuit-level simulators.
Circuit-level simulations are typically performed in several stages. During the first stage, referred to as node-extraction, static analysis of the circuit description is performed. From this analysis, information regarding the circuit's devices, their respective attributes and their connectivity is obtained. This information is subsequently combined with modules known as device models that describe the behaviour of each device on a mathematical level. In order to model the circuit's behaviour, the simulator must then solve a system of differential linear equations which is derived from all the information supplied to it during the node-extraction phase.
Although this method generates very accurate results, the technique is very computationally intensive, resulting in poor simulation speed. As a result, circuit-level simulation is usually not feasible for large designs and is therefore commonly used to simulate only the most critical subregions of a given circuit.   _{Your Comment}