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• Publié par: Musor
• Nombre de lectures: 19
• Langue: English

Extrait

A R C H I V E 2 0 0 6
Tutorial
“Differential Impedance And Insertion Loss Applied
To Sockets”
Eric Bogatin
Chief Technical Officer
Synergetix
COPYRIGHT NOTICE
• The papers in this publication comprise the proceedings of the 2006 BiTS Workshop. They reflect the
authors’ opinions and are reproduced as presented , without change. Their inclusion in this publication
does not constitute an endorsement by the BiTS Workshop, the sponsors, BiTS Workshop LLC, or the
authors.
• There is NO copyright protection claimed by this publication or the authors. However, each presentation
is the work of the authors and their respective companies: as such, it is strongly suggested that any use
reflect proper acknowledgement to the appropriate source. Any questions regarding the use of any
materials presented should be directed to the author/s or their companies.
• The BiTS logo and ‘Burn-in & Test Socket Workshop’ are trademarks of BiTS Workshop LLC.9
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Tutorial 2
2006
Differential Impedance and Insertion Loss Applied to Sockets Slide - 1 Differential Impedance and Insertion Loss Applied to Sockets Slide - 2
Outline
Who cares?
Differential Impedance and Insertion What design features influence insertion loss?
Loss Applied to Sockets What is impedance
Dr. Eric Bogatin
What design features influence impedance?CTO, Synergetix
Kansas City, KS What is differential impedance
[e-mail]
What design features influence differential impedance
2006 Burn-in and Test Socket Workshop What is differential insertion loss?
March 12-15, 2005
“It is better to uncover a little than to cover a lot”
- Francis Low
© Eric Bogatin 2006 www.BeTheSignal.com © Eric Bogatin 2006
Differential Impedance and Insertion Loss Applied to Sockets Slide - 3 Differential Impedance and Insertion Loss Applied to Sockets Slide - 4
Electrical Performance of Sockets For More Information
in Perspective
Constraints:• Performance • Vendors
• Corporate CultureCompliance
• Compatibility: Industry, Legacy
Pitchwww.BeTheSignal.com
Cycle lifetime
Online Lectures
Time between cleaning Cost: Feature Articles
$$$, TCOO, Electrical
PCD&M Monthly Signal Integrity Schedule, Risk
– DC resistance
Column: “No Myths Allowed” – Hi Frequency
– Signal IntegrityMaster Class Workshops Partitioning:» Bandwidth
» Insertion loss • Pin electronicsResources » Return loss • Wiring/cabling» SPICE models
• Loadboards– Power integrityPublished by Prentice Hall, 2004
» Loop inductance • Sockets
© Eric Bogatin 2006 © Eric Bogatin 2006
Differential Impedance and Insertion Loss Applied to Sockets Slide - 5 Differential Impedance and Insertion Loss Applied to Sockets Slide - 6
rdThe Socket as a Component 3 Best Alternative
• Specify values of model (circuit or behavioral) parameters• Purpose of an interconnect: “to transport a signal
Z
0from one point to another with an acceptable level of TD
Ldistortion”
C
Insertion loss
Return loss
• Specifications based on assumptions of the rest of the systemons
• Specifications are a pre-arranged compromise- sometimes based on:
System level simulation balancing cost-performance-constraints- (really hard!)
A guess
Because it worked in the last design
Enough margin for designer to sleep at night
Assuming performance is freeSimulated with HyperLynxWhat’s important to know?
Incorrect assumptions
1. Will the system work? Information that was passed from engineer to engineer to engineer to engineer…(only
one of whom might have an idea of what they want)2. Is the socket “good enough?”
3. How do you know before you build it and test it?
© Eric Bogatin 2006 © Eric Bogatin 2006
1March 12 - 15, 20069
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Tutorial 2
2006
Differential Impedance and Insertion Loss Applied to Sockets Slide - 7 Differential Impedance and Insertion Loss Applied to Sockets Slide - 8
Is this acceptable?
Universally used metric to define
Sometimes the frequency domain “goodness” of a socket:
offers an easier path to the answer
-1 dB insertion loss bandwidth No new information in the frequency domain
The only reason we’d ever leave the time
domain to go to the frequency domain:
To get to the answer faster.
© Eric Bogatin 2006 © Eric Bogatin 2006
Differential Impedance and Insertion Loss Applied to Sockets Slide - 9 Differential Impedance and Insertion Loss Applied to Sockets Slide - 10
Transmitted Signals in the
Two World Views
Frequency Domain
Time domain view
What are signals in the frequency domain?
only sine waves
incident
transmitted
Frequency domain view reflected
amplitude amplitude
amplitudeincident phase phase
phase
transmitted
Everything you ever wanted to know about the performance of a socket is
contained in the reflected and transmitted signalsUp to the highest sine wave frequency that is significant
© Eric Bogatin 2006 © Eric Bogatin 2006
Differential Impedance and Insertion Loss Applied to Sockets Slide - 11 Differential Impedance and Insertion Loss Applied to Sockets Slide - 12
Terminology Most Important Caveat
Source Termination incident impedance impedance
= 50 Ohms = 50 Ohms
transmitted
incident
transmitted
Vtransmitted
What’s important: at each frequency • The source impedance and the load impedance when defining V S21 is always 50 Ohms.incident
• Also called: • Insertion loss has significance if the end use environment is 50
Insertion loss Ohms
S21
Transfer function S21 isS21 is dommi inated by how the i immpedance of the socket
matches the impedance of the test environment!
There is a magnitude and a phase at each frequency
© Eric Bogatin 2006 © Eric Bogatin 2006
2March 12 - 15, 20069
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Tutorial 2
2006
Differential Impedance and Insertion Loss Applied to Sockets Slide - 13 Differential Impedance and Insertion Loss Applied to Sockets Slide - 14
The Value of “-1 dB Insertion Loss
Good and Bad Insertion Loss
Bandwidth” as a Metric
1.0 • Relative comparison
0.9 good
0.8 • First pass screening
0.7
0.6 • Rough, rule of thumb for usable operating frequency0.5
0.4 Is this good? Is it good enough?
0.3 • Should not be used to sign off on a design
1.0
0.2 bad 0.9 too approximate
0.1 0.8
0.0
0.7 too much margin? Too little?
022 4 6 8 10 12 14 16 180
0.6
Too many assumptions0.5freq, GHz
0.4
0.3 • Multiple approximations:
Simulated with Agilent ADS 0.2
Bandwidth of the signal
0.1
0.0 Is the system a 50 Ohm system?
022 4 6 8 10 12 14 16 180
Total system budget
freq, GHz• Is there a difference between Allocation to the socket
good
-1 dB = 90% transmitted signal amplitude • A better approach (and much more expensive):good enough
-2 dB = 80% tritted signal amplitude Model and simulatebetter ?
-3 dB = 70% transmitted signal amplitude
© Eric Bogatin 2006 © Eric Bogatin 2006
Differential Impedance and Insertion Loss Applied to Sockets Slide - 15 Differential Impedance and Insertion Loss Applied to Sockets Slide - 16
The Simplest Model of a
What Affects Insertion Loss of a Socket?
Transmission Line
Microstrip1. Matched Impedance
2. Controlled impedance A "-1" order model:
Any two conductors with length3. Discontinuities of load board
4. Length
5. Dielectric loss
6. Conductor loss Length
7. DC contact resistance
Lead frame of an IC Package
© Eric Bogatin 2006 © Eric Bogatin 2006
Differential Impedance and Insertion Loss Applied to Sockets Slide - 17 Differential Impedance and Insertion Loss Applied to Sockets Slide - 18
Labeling the Conductors The Signal
Vsignal
V
Signal path
Signal path
V Vin
Return path
GROUND GROUND
Return path
© Eric Bogatin 2006 © Eric Bogatin 2006
3March 12 - 15, 2006
Insertion Loss (magnitude)
Insertion Loss (magnitude)Tutorial 2
2006
Differential Impedance and Insertion Loss Applied to Sockets Slide - 19 Differential Impedance and Insertion Loss Applied to Sockets Slide - 20
How fast does a signal move down
Instantaneous Impedance
a line?
v
Vsignal
V
signal
Signal pathε
return
Return path
in air: v = 186,000 miles per sec v = 12 inches/nsec
• Signal sees an “instantaneous impedance” each step along the pathinches inches12 12n sec n sec inches • Instantaneous impedance depends on the geometry of signal and return pathv = = = 6 n sec • A controlled impedance when instantaneous impedance is constant24
• One impedance that characterizes the interconnect:
• Characteristic impedance
© Eric Bogatin 2006 © Eric Bogatin 2006
Differential Impedance and Insertion Loss Applied to Sockets Slide - 21 Differential Impedance and Insertion Loss Applied to Sockets Slide - 22
Characteristic Impedance and Most Important Features of
Characteristic Impedance Capacitance per Length
capacitance per length • Characteristic impedance is not about the signal path