Wire load models

1.    Wire load models

Extraction data from already routed designs are used to build a lookup table known as the wire load model (WLM). WLM is based on the statistical estimates of R and C based on “Net Fan-out”.

For fanouts greater than those specified in a wire load table, a “slope factor” is specified for linear extrapolation.

wire_load (“5KGATES”) {

resistance : 0.000271 -------------> R per unit length

capacitance : 0.00017 -------------> C per unit length

slope : 29.4005 ---------------------> Used for linear extrapolation

fanout_length (1, 18.38) ----------> (fanout = 1, length = 18.38)

fanout_length (2, 47.78)

fanout_length (3, 77.18)

fanout_length (4, 106.58)

fanout_length (5, 135.98)

}

Eg:

Fanout = 7

Net length = 135.98 + 2 x 29.4005 (slope) = 194.78 ----------> length of net with fanout of 7
Resistance = 194.78 x 0.000271 = 0.05279 units
Capacitance = 194.78 x 0.00017 = 0.03311 units