Subject: RE: [IBIS-Users] Input ESD Structures
From: Lynne Green (lgreen@cadence.com)
Date: Tue Apr 23 2002 - 08:28:33 PDT
Hello, Tim,
The 3 most significant DC parameters in the diode model:
IS: "reverse leakage" current, adjusted to give correct forward current
at low bias voltage (V<0.4V in silicon). Ranges from around 1e-16
for signal diodes to >1e-9 for power diodes.
N: ideality factor, adjusted to give correct forward current at medium
bias (0.5V to 0.6V in silicon). Usually 1<N<2.
RS: series resistance, adjusted to give correct forward current at
high bias (V>0.7V in silicon). Typically 0.1 to 10 ohms.
You need at least 3 I-V points to get these parameters. More will
give a better least-squares fit.
Model needs to be accurate over actual operating conditions,
including reflections. This should cover from Vcc of reverse
voltage to about 1V of forward voltage. Maximum current should not
exceed 100 mA, even outside this region. SiQual has addressed
diode models in the reflector, with comparison to measurements.
Best regards,
Lynne
Dr. Lynne Green
PCB Systems Division
Cadence Design Systems, Inc.
-----Original Message-----
From: Timothy Coyle [mailto:Timothy.Coyle@nsc.com]
Sent: Monday, April 22, 2002 11:51 AM
To: ibis-users@eda.org
Subject: [IBIS-Users] Input ESD Structures
Hello,
When I get a SPICE netlist from the design team to do a spi2ibis translation, the ESD structures have ideal diodes (no resistance) which leads to kAmps in my
power and ground clamp curves. So I put a series resistor of 1-3 Ohms on the input of the ESD pad (and sometimes the ground node of the ESD pad) to try to limit
the current. While this approach works, my simulated data does not match up with data taken from the bench. The lab data at one point is 4.3mA and the simulated
data at the same point is 160uA for a ground clamp curve. Changing the resistor value doesn't give me the right current either. Does anyone have any
comments/suggestions on this approach?
Also, I'm wondering what type of affect on my input model the magnitudes of my power and ground clamp curves have. Does it matter to a simulator if the ground clamp
current is 4.3mA or 160uA? It seems the most important parameter for an input model is Ccomp. Has anyone done any work on this they would like to share?
Many thanks again to those who respond,
Tim
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