The I/O buffer information specification, or IBIS, is a simulation ... voltage input. IBIS modelers use data from the designer’s SPICE stack simulations or bench data. For instance, Table 1 shows a ...

So, with zero input current, both Q1 and Q3 conduct Ibias, as does Q2 and Q4 and the circuit acts with a differential output. Figure 3 LTspice simulation of differential output in response to small ...