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# E. Voltage Dependent Voltage Source

Symbol Names: E, E2

There are three types of voltage-dependent voltage-source circuit elements.

Syntax: Exxx n+ n- nc+ nc- <gain>

This circuit element asserts an output voltage between the nodes n+ and n- that depends on the input voltage between nodes nc+ and nc-. This is a linearly dependent source specified solely by a constant gain.

Syntax: Exxx n+ n- nc+ nc- table=(<value pair>, <value pair>, ...)

A look-up table is used to specify the transfer function. The table is a list of pairs of numbers. The second value of the pair is the output voltage when the control voltage is equal to the first value of that pair. The output is linearly interpolated when the control voltage is between specified points. If the control voltage is beyond the range of the look-up table, the output voltage is extrapolated as a constant voltage of the last point of the look-up table.

Syntax: Exxx n+ n- nc+ nc- Laplace=<func(s)>
+ [window=<time>] [nfft=<number>] [mtol=<number>]

The transfer function of this circuit element is specified by its Laplace transform. The Laplace transform must be a function of s. The frequency response at frequency f is found by substituting s with sqrt(-1)*2*pi*f. The time domain behavior is found from the impulse response found from the Fourier transform of the frequency domain response. LTspice must guess an appropriate frequency range and resolution. The response must drop at high frequencies or an error is reported. It is recommended that LTspice first be allowed to make a guess at this and then check the accuracy by reducing reltol or explicitly setting nfft and the window. The reciprocal of the value of the window is the frequency resolution. The value of nfft times this resolution is the highest frequency considered. The Boolean XOR operator, "^" is understood to mean exponentiation "**" when used in a Laplace expression.

Syntax: Exxx n+ n- value={<expression>}
This is an alternative syntax of the behavioral source, arbitrary behavioral voltage source, B.

Syntax: Exxx n+ n- POLY(<N>) <(node1+,node1-) (node2+,node2-)+ ... (nodeN+,nodeN-)> <c0 c1 c2 c3 c4 ...>

This is an archaic means of arbitrary behavioral modeling with a polynomial. It is useful for running legacy opamp models.

Note: It is better to use a G source shunted with a resistance to approximate an E source than to use an E source. A voltage controlled current source shunted with a resistance will compute faster and cause fewer convergence problems than a voltage controlled voltage source. Also, the resultant nonzero output impedance is more representative of a practical circuit.