Steven Chiang of Trust-Tek Corporation addresses the challenges implementers face adhering to certain key requirements defined in the specifications, such as receiver stressed eye testing, while operating within contexts that do not warrant a literal interpretation of the methodology described in these specifications. He also offers best practices in test and focuses on contextual requirements and separating component-level testing/characterization needs from system-level ones.

1. Mohamed Hafed & Steven Chiang
Introspect Technology & Trust-Tek Corporation
Practical Experiences in MIPI D-PHYSM
and C-PHYSM Receiver Testing

2. © 2017 MIPI Alliance, Inc.
In Theory…
2
DUTTest Instrument

3. © 2017 MIPI Alliance, Inc.
In Real Life…
3
IP Bring-Up
• Test IP in isolation
• Theoretical case
(perhaps!)
Component Bring-Up
• Focus on entire chip
functionality including
interface
• Other effects start to
appear
Application Module
Bring-Up
• Where is the receiver?
• Where is the channel?
• What stimulus to use?
Test Requirements Through Product Lifecycle Stages

4. © 2017 MIPI Alliance, Inc.
Agenda
• Overview of receiver test
• Illustration of practical module implementations and
evaluation platforms
• Recommendations and best practices
4

5. © 2017 MIPI Alliance, Inc.
Physics of Signal Transmission
5
Transmitter
Large Signal
Small Noise
Channel (cable, connector, flex PCB, package)
Receiver
Small Signal
Large Noise

6. © 2017 MIPI Alliance, Inc.
Objective of Receiver Test
6
Generate a stressed signal as if it went
through a channel
- Model ISI
- Model DCD
- Model Jitter
Receiver
Small Signal
Large Noise

7. © 2017 MIPI Alliance, Inc.
MIPI D-PHYSM Receiver Specification
7
MIPI D-PHYSM
Generator
Data Rx
Clock Rx
Reference Channel
Reference Channel

8. © 2017 MIPI Alliance, Inc.
MIPI C-PHYSM Receiver Specification
8
MIPI C-PHYSM
Generator Data RxReference Channel

9. © 2017 MIPI Alliance, Inc.
The Linear Channel Model
9
Freq
|S21|
ΦS21
Freq
Freq
Grp Delay
S21

10. © 2017 MIPI Alliance, Inc.
The Linear Channel Model
10
Linear Channel
Timing Edges Largely Unaffected
in a Linear Channel

11. © 2017 MIPI Alliance, Inc.
The Linear Channel Model
11
Linear Channel
Timing Edges Largely Unaffected
in a Linear Channel
Results in almost non-realistic
jitter injection requirements

12. © 2017 MIPI Alliance, Inc.
Practical Evaluation Board… Nonlinear!
12
IC
Test Instrument
FlexFlex
Discontinuity
(Connector)
Discontinuity
(Connector)
Bend or ViaDiscontinuity
(Test Point)
Discontinuity
(Connector)
Discontinuity
(Connector)

13. © 2017 MIPI Alliance, Inc.
Linear Channel Versus Non-Linear Channel
13
Tx Eye Diagram
Linear Channel Eye Diagram (~0.3 UI Closure)

14. © 2017 MIPI Alliance, Inc.
Linear Channel Versus Non-Linear Channel
14
Tx Eye Diagram Non-Linear Channel Eye Diagram (~0.4 UI Closure)
Channel is 25% Shorter

15. © 2017 MIPI Alliance, Inc.
Practical Experiences: Skew
15
IC
Test Instrument
FlexFlex
Bend or Via

16. © 2017 MIPI Alliance, Inc.
Practical Experiences: Skew
16
Pos
Neg
Pos
Neg
Common Mode
Skew introduces common-mode noise (not good for receiver!)
Difficult to detect on differential scope eye diagram

17. © 2017 MIPI Alliance, Inc.
Practical Experiences: Reflections
17
IC
Test Instrument
FlexFlex
Discontinuity
(Connector)
Discontinuity
(Connector)

18. © 2017 MIPI Alliance, Inc.
Practical Experiences: Reflections
18
Worst-case example of a
channel non-linearity
Signal rise time is sharp,
but reflections can cause
bit flips

19. © 2017 MIPI Alliance, Inc.
Practical Experiences: Reflections
19
Stub Causing Complete Eye Closure Slowing Data Rate Reveals Stub Waveform

20. © 2017 MIPI Alliance, Inc.
Practical Experiences: Grounding
20
IC
Test Instrument
FlexFlex
Connector
Connector

21. © 2017 MIPI Alliance, Inc.
Practical Experiences: Grounding
21
HS eye diagram affected by CM and Diff effects
LP waveforms affected by crossing levels and reflections

22. © 2017 MIPI Alliance, Inc.
Practical Experiences: Inductance
22
IC
Test Instrument
FlexFlex
Discontinuity
(Test Point)

23. © 2017 MIPI Alliance, Inc.
Practical Experiences: Inductance
23
Often due to test points
Makes correlation with
specifications difficult

24. © 2017 MIPI Alliance, Inc.
Recommendations
24
Adopt a system-level approach to test if your evaluation board
looks like a system
Identify stress parameters suitable for characterizing your device
in its environment
Characterize receiver performance across system constraints as
well as through ideal “linear” channel