Quartus® Prime Pro Edition User Guide: PCB Design Tools

ID 683768
Date 4/01/2024
Document Table of Contents

1.4.2. Elements of an IBIS Model

An IBIS model file (.ibs) is a text file that describes the behavior of an I/O buffer across minimum, typical, and maximum temperature and voltage ranges with a specified test load.

The tables and values specified in the IBIS file describe five basic elements of the I/O buffer.

The following elements correspond to each numbered block.

  1. Pulldown—A voltage-current table describes the current when the buffer is driven low based on a pull-down voltage range of –VCC to 2 VCC.
  2. Pullup—A voltage-current table describes the current when the buffer is driven high based on a pull-up voltage range of –VCC to VCC.
  3. Ground and Power Clamps—Voltage-current tables describe the current when clamping diodes for electrostatic discharge (ESD) are present. The ground clamp voltage range is –VCC to VCC, and the power clamp voltage range is –VCC to ground.
  4. Ramp and Rising/Falling Waveform—A voltage-time (dv/dt) ratio describes the rise and fall time of the buffer during a logic transition. Optional rising and falling waveform tables can be added to more accurately describe the characteristics of the rising and falling transitions.
  5. Total Output Capacitance and Package RLC—The total output capacitance includes the parasitic capacitances of the output pad, clamp diodes (if present), and input transistors. The package RLC is device package-specific and defines the resistance, inductance, and capacitance of the bond wire and pin of the I/O.
Figure 2. Five Basic Elements of an I/O Buffer in IBIS Models