The Input/Output Buffer Information Specification (IBIS) is being developed by the IBIS Open Forum, which is affiliated with the Electronic Industries Alliance (EIA). IBIS specifies a standard form for presentation of information in ASCII format in special files. This information describes behavior of various I/O buffers that send electrical signals outside the silicon chip or receive such signals. The type of information includes output I-V curves for output buffers in LOW and HIGH states, V(t) curves describing the exact form of transitions from LOW to HIGH states and from HIGH to LOW states for a given load, values for die capacitance, electrical parameters of the packages, and so on. The IBIS standard only specifies the "form" of information and does not specify how the information should be processed or used by the simulator.
However, the IBIS standard contains a section devoted to recommendations on how information should be derived through the simulation or from the silicon measurement. In addition, the IBIS Open Forum has sponsored development of a parser for IBIS files--called the golden parser. The golden parser is freely available as an executable and should be used for verification of IBIS files. The golden parser is incorporated into Hspice. When the golden parser processes an IBIS file, it produces warnings and/or error messages which by default appear in the Hspice output.
Star-Hspice implements I/O buffers as a new element type, which we refer to as a buffer. The name of this element starts with the letter b. Using buffers is similar to using other Star-Hspice elements, such as transistors: give a name to the buffer, specify a list of nodes that are used to connect the buffer to the rest of the circuit, and specify parameters. Only parameters that specify a model for the buffer (file name and model name) are required.
Two significant differences from the use of other elements are: (1) number of external nodes is variable depending on the buffer type and can be from 4 to 8; and (2) nodes that are suppose to connect to power/ground rails must not be connected in the netlist because Star-Hspice does this connection by default.
This chapter is not intended to introduce the IBIS standard because it is a large document; familiarity with the standard is assumed. A significant amount of information is available on the internet and appropriate links to other sites are given in References.
Three types of analysis are supported for input/output buffers:
This chapter covers the following topics: