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:<math> i(t) = C \frac{dv}{dt} </math>

:<math> v(t) = L \frac{di}{dt} </math>

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== An Analog Differentiator Macromodel ==

:<math> \frac{ v_{out} }{ v_{in} } = - \frac{R_1}{1/sC_1} = -s \left( R_1C_1 \right) </math>

which represents a derivative operator in the Laplace s-domain.

An equivalent macromodel of the above circuit is given in the following figure. This is RF.Spice's "Analog Differentiator Block". In this model, the ideal Op Amp has been replaced with the linear controlled voltage source E2:

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== An Analog Integrator Macromodel ==

A practical voltage integrator circuit using an ideal Op Amp is shown in the opposite figure. The voltage transfer function of this circuit is given by:

which represents a integral operator in the Laplace s-domain. This circuit is very similar to the Op Amp differentiator except for the fact that the timing resistor and capacitor have switched places.

An equivalent macromodel of the above circuit is given in the following figure, which represents RF.Spice's "Analog Integrator Block". In this model, the ideal Op Amp has been replaced with the linear controlled voltage source E2:

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You can access all these blocks from the '''Parts Menu'''. Some of the waveform generator devices are categorized as "voltage source" devices in the Device Manager's point of view. A number of the virtual blocks are native XSPICE models. You can find their models as "process models" in the Device Manager. Many others are "subscircuit models". You can open up, view and even modify their Netlist codes. Some other blocks like the generalized analog and digital filters do not have editable Netlist codes.

Most of the virtual blocks can be used in both transient and AC analysis tests. Obviously, nonlinear operations must be performed in the time domain. For example, you can see the performance of voltage controlled oscillators (VCO) only in a transient test, and using them in conjunction with AC frequency sweep analysis is meaningless. The same is true for frequency conversion blocks such as frequency multipliers. In addition, certain blocks such frequency conversion blocks may require harmonic wave input signals and may not work properly with arbitrary waveforms.

When your circuit involves several interconnected virtual blocks, the SPICE simulation of your circuit is likely to encounter convergence problems. This is more frequent when you a transient analysis of such circuits. In those case, we recommend that you change the SPICE integration method. You can do this by opening the '''SPICE Simulation Options''' dialog from the Simulate Menu. There are two options available: trapezoidal or gear. The default option is "trap". Changing the integration method to "gear" can improve the convergence of the transient analysis.

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