Re: [SI-LIST] : SCSI-LVDS Models

jjcahill@us.ibm.com
Tue, 29 Jun 1999 08:34:53 -0500

Many differential receivers have circuits with high gain or even positive
feedback, each of which can cause convergence problems for simulators. Review
the circuit to determine if it has those characteristics. If I encounter a
circuit that the simulator has trouble determining a DC state for I start the
signal sources and power supply voltages at 0 to make the DC state solution
trivial and then slowly ramp the sources and supplies to the intended starting
point, letting it settle there and then doing the interesting portion of the
simulation. Simulator transient solution algorithms seem to be better at
handling dynamic behavior in the circuit than the dc algorithms. Specifying the
initial conditions for crucial nodes and elements in the circuit is another way
to aid the DC algorithm, but you must get the correct 'crucial' nodes or you
will have continuing convergence problems.

Joe

CEC Analysis and I/O Design
Phone: 507.253.0762 Fax: 507.253.4966
jjcahill@us.ibm.com

"Chan, Michael " <Michael.Chan@COMPAQ.com> on 06/28/99 02:18:28 PM

Please respond to si-list@silab.eng.sun.com

To: "'si-list@silab.eng.sun.com'" <si-list@silab.eng.sun.com>
cc: (bcc: Joe Cahill/Rochester/IBM)
Subject: [SI-LIST] : SCSI-LVDS Models

Hi SI Guru:
We are trying to do some Hspice simulations on SCSI bus to
investigate signal quality. One problem that we encountered is the
convergence
problem of Hspice. We are still not sucessful in bringing the spice
simulation to converge after we have tried different convergence aids as
suggested in
the Hspice manual. We plan to replace most of the receiver models with
passive lumped models ( i.e. one resistor and one capacitor for CMOS input
buffer ) and see whether this will help. Can anyone suggest what an
equivalent model will be for a LVDS input receiver will be? Any suggestion
will be appreciated.

Regards,
Michael Chan
Compaq Computer Corp.
Michael.Chan@compaq.com

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