Differential Pins

Differential pins refer to the relationship between buffers. Differential pins are specified in the "Component Description" section of the IBIS standard. The following examples explain how differential pins can be simulated with the Star-Hspice implementation of IBIS.

Figure 19-12: Output buffers

You must use two separate buffers, each of which is specified by a separate card in the netlist. They are related only through their input, which is differential.

The only way the inverter can implement in this situation is by specifying two independent voltage sources that have opposite polarity.

Figure 19-13: Input buffers

Nodes out_of_in_1, out_of_in_2 must be specified but are not used. In the case of differential input buffers, the voltage will be probed between nd_in_1 and nd_in_2 and processed by a voltage dependent voltage source as described below.

V_diff is a differential voltage parameter from the IBIS file (default is 200 mV). Add definition of parameter V_diff , voltage controlled voltage source E_diff_out_of_in , and a resistor R_diff_out_of_in.

Example

.PARAM V_diff = 0.2

E_diff_out_of_in diff_out_of_in 0 PWL(1) nd_in_1 nd_in_2

+ '- V_diff' 0 '+ V_diff' 1 R_diff_out_of_in
+ diff_out_of_in 0 1x

Use the voltage across R_diff_out_of_in as the output of the differential input buffer.

If V(nd_in_1) - V(nd_in_2) < V_diff, V(diff_out_of_in) = 0

if V(nd_in_1) - V(nd_in_2) > V_diff, V(diff_out_of_in) = 1