eldo_user

Figure 17-5. 3_state Buffer Model Building Blocks
IBIS Models Support in Eldo
Buffers
3_state_ECL buffer differs mainly from 3_state buffer in that the a_pdref is internally
connected to the a_puref; that is, pull-up and pull-down share the same power reference. 3_state
and 3_state_ECL buffers also differ in the conventions related to [Pulldown], [Temperature
Range], [Pin Mapping] keywords and the measuring conditions of the switching characteristics.
Buffers with Open Drain, Sink, or Source
The open drain and open sink are buffers that do not include a pull-up network; that is, the
output can sink current only. Earlier IBIS versions used the term “open drain”, however, this
may be confusing for NMOS and PMOS networks, and so the term “open sink” is now used to
describe a buffer that can sink current only. The “open drain” terminology is retained for
backward compatibility.
The open source buffer is a buffer that does not include a pull-down network; that is, the output
can source current only.
Pseudo-Differential Buffers
The [Diff Pin] keyword in the IBIS file is used to create a pseudo-differential buffer from two
already existing single-ended buffers.
A pseudo-differential input buffer consists of two single-ended input buffers as shown in
Figure 17-6. The digital outputs of these two single-ended buffers are tied together and labeled
by d_receive. One single-ended buffer’s input is taken to be the non-inverting input
Eldo® User's Manual, 15.3 739