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R — Resistor

The resistor is the most basic passive component, opposing the flow of current according to Ohm's law.

Syntax

R<name> <node+> <node-> <value> [TC=<tc1>[,<tc2>]] [M=<m>]
R<name> <node+> <node-> <model_name> [L=<length>] [W=<width>]
R<name> <node+> <node-> VALUE={<expression>}
Parameter Description
node+, node- Positive and negative terminal nodes
value Resistance in ohms
TC=tc1[,tc2] Temperature coefficients (linear, quadratic)
M=m Multiplier (parallel instances)
model_name Reference to a .MODEL definition
VALUE={expr} Behavioral expression

Examples

* Basic resistor
R1 IN OUT 1k

* With engineering notation
R2 A B 4.7MEG

* Temperature-dependent
R3 IN OUT 10k TC=0.001,0.0001

* Model-based with geometry
R4 IN OUT rmod L=10u W=2u

* Behavioral (expression-based)
R5 IN OUT VALUE={1k * (1 + V(CTRL))}

LTspice Resistor Compatibility

With CompatibilityOptions.LTspice, resistor instance parasitics are synthesized by the parser as helper components:

R1 IN OUT 1k Rser=0.5 Rpar=10Meg Cpar=0.2p

Rser=<value> adds a series resistor through an internal node. Rpar=<value> adds a resistor across the original resistor terminals, and Cpar=<value> adds a capacitor across the original resistor terminals. The core resistor model is not changed.

MNA View

A resistor is the simplest matrix stamp. The simulator converts resistance to conductance:

$$ g = \frac{1}{R} $$

For a resistor between nodes p and n, the current is:

$$ i = g(V(p)-V(n)) $$

That contributes only matrix coefficients:

Y[p,p] += g
Y[p,n] -= g
Y[n,p] -= g
Y[n,n] += g

No extra branch-current unknown is needed, and no integration history is owned by a resistor. In transient analysis, resistors still matter because they set RC and RL time constants and damping.

See How SpiceSharp Solves Circuits for the full matrix assembly algorithm.

Model Definition

.MODEL rmod R(RSH=100 NARROW=0.1u)

Temperature Dependence

With temperature coefficients:

$$ R(T) = R_0 \left[1 + TC_1(T - T_{\text{nom}}) + TC_2(T - T_{\text{nom}})^2\right] $$