From: Bo ([email protected])
Date: Mon Feb 19 2001 - 18:20:04 PST
Hi Everybody, BO 2 0 2001-02-20T02:00:00Z 2001-02-20T02:00:00Z 2 702 4004 Yahoo 33 8 4917 9.2720 0 6 pt 6 pt 0
Hi Everybody,
I am interested in finding a way to easily estimate thequality of a package and its internal decoupling scheme with a decent level ofaccuracy.��
What I could probably do for a start is to look at the viasfor each power supply in the package and determine the total inductance forseveral paths inside of the package.�What I mean by "path" is the total inductance that will beseen due to vias for a vias connecting a package ball to the internal packageplane designated for power supply A or path of vias connecting one side ofinternal decap to the power supply plane inside the package.� I would probably disregard the inductance ofthe package planes since they are typically not as inductive as the vias.� So fine given that I can accuratelycalculate via inductances through the package I could probably create a simpleSpice circuit that will recreate package inductances plus decouplingcapacitors.�� Now what typically happensduring normal operation of a circuit is that current flows through powersupplies.� While circuit switches thesudden demand/change for/of the current will cause a voltage drop accross thepackage inductance (any!
one ever heard of "ground bounce"? :-) ).� So my questions are:� How to determine quality of the packagegiven this simple model?� Whatultimately person desires(me being one of them) is to determine if this packagewill be able to give less than X,Y,Z amounts of noise on the power supplies� A, B, C given that the chip containsgazillion transistors in its core and xxx number of HSTL I/O's, nnn number ofTTL I/O's, rrr number of LVDS I/O's, and PCI bus that is gg bits wide runningat frequency of www MHz.� Or what if Iincrease number of LVDS I/O's by 2 will the package still work?
The one option is to put a full chip model of the die thatcontains all these transistors, add a package model and run it.� Few billion years later you might getresult. If it ever converges of course.�Other way is to somehow scale all the values in the circuit and try itthat way.�� I have tried this andscaling is rather tricky.� It will giveyou better estimate as you make your model larger and larger.� But this will come at the cost of the speed.Yet another way is to use this simple package model, stick a current sourcesbetween power supply connection at the die and ground connection at the die andstart pumping current.� Hmmmm.� Is this right approach?� I have feeling that I am missingsomething.� And also I am not sure whatwould be correct values for current spikes in terms of switching rate as wellas amplitude.� They, current amplitudeand switching rate, will depend on the type of the I/O buffers and core of thechip, that is what I know.� But cansomeone suggest typical values?!
� Or howto find these values?� If I have morethan one power supply in the circuit should you also connect a current sourceto other poewr supplies the same way and then simulate?.� But if I want to find out which supplycauses most of the problems shouldn't be better to simulate only one powersupply drawing current while others remain "silent"?� And if they are "silent" what shouldbe connected to the die end of the power supply?� Any suggestions?
A simple diagram of a package
D
I
E
������������������������������ ���������������������internal decap
������ power supplydie��������������� -------||--------�������� ground on the die
---------------||||-----------------------||||--------------|||||--------------------|||||--
��������������������|��������������������������������|�������������������� |���������������������������� |
��������������������|��������������������������������|�������������������� |���������������������������� |
�P����������������� |������ Power Plane��� |�������������������� |�������������� ��������������|
A����������������� |---------|--------------|��������������������|����������������������������|�
C������������������������������� |���������������������������������������� |���������������������������� |
K������������������������������� |���������������������������������������� |� Ground Plane�� |
A������������������������������ |���������������������������������������� |----|-----------------|
G������������������������������� |���������������������������������������������� |
E��������� ����������������������|����������������������������������������������|�����������������������������������������
��������������������������������� |���������������������������������������������� |
��������������������������������� |���������������������������������������������� |
-------------------------||||---------------------------------||||----------------�������������������
������ power supplyon the pcb���������������� ground on thepcb
P
C
B
Any suggestions will be greatly appreciated.
Thank you for your time,
Regards,
Bo
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