Subject: Re: [IBIS-Users] Validating IBIS Inputs
From: Robert Haller (rhaller@sisoft.com)
Date: Tue May 13 2003 - 12:12:28 PDT
Tim,
One way to verify IBIS input buffer clamps is by running a simulations
using a ideal voltage source driving through a low resistance and high
etch impedance. i.e. Voltage source of V=Vdd, Tr = 500ps,resistor of 10
ohms and a Tline of Zo=75 ohms/TD=4ns,and/or 1ns.
The clamps will turn on because the signal will overshoot at the end of
the line. By utilizing ideal circuit elements you have eliminated all
the other variables. You will also be able to validate the input
capacitance of your receiver.
The choice of 75 ohms impedance of the transmission line is not
critical. The impedance must be high enough to guarantee turning on the
clamps. The combination of the driver output impedance and the
transmission line forms a voltage divider, which defines the initial
amplitude as the wave leaves the driver. When the wave reaches the end
of the unterminated transmission line it doubles.
You can compare your IBIS simulations to Spice or bench or both.
For more information refer to "Constructing Accurate Behavioral Models
of I/O Buffers" ISBN 0-933-217-47-1 Designcon98 (HPSDC).
regards.
Bob
-- Robert J. Haller (rhaller@sisoft.com) Principal Consultant Signal Integrity Software Inc. 6 Clock Tower Place, Suite 250 Maynard, MA 01754 Phone: (978) 461-0449, ext 15Timothy Coyle wrote: > Hello, > I'm curious as to how other people validate an IBIS input buffer with a ground clamp and power clamp curve to the original > SPICE netlist. If I run a simulation of a driver and receiver with a transmission line, and then a driver with a transmission > line and a lumped capacitor load, I get almost the same result. (Assuming a properly made IBIS file) The power and ground clamp > curves only turn on below Reference Ground or above supply voltage. So if I have an input going into my input buffer that has overshoot > then should I see my powerclamp curve turn on? What types of tests do people do to validate that the clamps are behaving as expected? > (And feel free to inform me on what the expected behavior of the clamps should be) > > Thanks in advance, > > Tim > |------------------------------------------------------------------ >
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