Re: Stored Charge by Peivand Tehrani

Peivand,

I looked at your simulation example, and I think that you are referring to a
phenomena as the "glitch" which is unrelated to the "kickback effect", commonly
associated with the charge storage effects (discussed in BIRD34) of clamping
diodes, ESD structures, etc.

In my opinion the glitch you are observing is related to the parasitic
capacitances between Drain-Source, Gate-Source, and Gate-Drain. When the gate
voltage of the inverter begins to switch, there is a time period when none of
the output transistors are (fully) on. The changing voltage on the gate bleeds
through the parasitic capacitances to the output untill the transistor to be
turned on gets turned on. Since we are talking about an inverter, this causes a
glitch that goes the opposite direction of the intended edge. If you try to
reproduce the same effect with a "voltage follower" circuit, you will see that
the "glitch" will go in the same direction with the intended edge.

Arpad Muranyi
Intel Corporation
================================================================================

Author: owner-ibis@vhdl.vhdl.org at SMTPGATE
Date: 7/19/96 5:50 PM
Priority: Normal
TO: bob@icx.com at SMTPGATE
CC: ibis@vhdl.org at SMTPGATE
BCC: Arpad Muranyi at FMCCM28
Subject: Stored Charge
------------------------------- Message Contents -------------------------------
Hello IBIS fans,

   I was reviewing the stored charge BIRD 34.1 . I have observed the
same glitch effect even with ESD diodes removed. So I think this glitch
is not just created by the stored charge in the diodes. This glitch can
easily be observed with a simple CMOS invertor with a fast (100 psec)
ramp as the input of the invertor, I think this glitch is because of the
stored charge in the depletion region of upper and lower devices.

   I will send a simple SPICE file that I have been using to simulate this
effect. The SPICE version which I am using runs into convergence problems
if I remove Cd1 capacitor. This capacitor presents the die capacitor in
IBIS models. After the simulation the voltage at node 2 should be probed.

Best Regards,
Peivand Tehrani.

**************************SPICE file************************

Driver Device Transitions For Gate Transition
*************************************************************
VDD 3 0 5
*************************************************************
M1 2 1 0 0 QN L=1.5E-6 W=136.4E-6
M2 2 1 3 3 QP L=1.5E-6 W=341E-6
*************************************************************
.MODEL QN NMOS(LEVEL=1 VTO=1.0 TOX=250E-10 NSUB=1E16 UO=500 )
.MODEL QP PMOS(LEVEL=1 VTO=-1.0 TOX=250E-10 NSUB=1E16 UO=200)
*************************************************************
VIN1 1 0 PULSE(5 0 0 .01n 0 100E-9 1E-3)
*************************************************************
Cd1 2 0 4p
R11 2 0 50
*************************************************************
.tran .001n 1n
.END
Received on Tue Jul 23 10:50:46 1996