High-Speed Noise and Grounding
More Black Magic
Dr. Howard Johnson
This two-day class focuses on mixed-signal applications involving high-speed digital electronics used in conjunction with sensitive analog circuits such as radio receivers, GPS devices and cell phones. This course addresses the critical issues of noise and grounding that are seen in many advanced signal processing applications today, including avionics, telemetry and guidance systems.
The motivation for this course is described in the somewhat tongue-in-cheek article: Digital Engineers Don't Believe in EMC.
|Mixed-signal isolation||Isolated ground layout|
|Ground bounce (SSO)||Cuts in ground plane|
|Power filtering for PLL's||System test|
|Flex circuit cross-hatch||Coaxial shielding|
|Asynchronous clock regions||Electrostatic discharge|
Chapter 1: Principles of Mixed Signal Isolation
- Common-impedance coupling
- Measuring capacitance
- Measuring inductance
- Frequencies That Matter for Digital Signals
- Ways to Reduce Crosstalk
Chapter 2: Ground Bounce (SSO)
- In the presence of fast-changing magnetic fields you can only measure voltages between nearby points
- Example: measure the "inductance of a via"
- Confront the distributed nature of inductance
- BGA package crosstalk (SSO coupling) varies with pin separation, package height, and signal rise/fall time
Film: BGA Ground Ball Placement
- This 40 min. film presents the theory of SSO crosstalk in BGA packages with examples, giant scale models, and measured lab results.
Chapter 3: PCB Layer Stack
- The Path of Returning Signal Current
- Example: Low-Level Audio-Frequency Crosstalk
- Common-mode Chokes, Short Ground Connections, and Differential Probes
- Magnetic Fields Wrap Around the Back Side of Your PCB
- Stacking Connectors
- When to Segment the VCC Plane
- Moat and Drawbridge Construction
- Does the Moat Work at RF?
Chapter 4: System-Level Grounding
- Picture Frame Analysis
- Three Big Ideas For Isolation (i.e., Reducing the Impact of Stray Current)
- Capacitance Between Boards
- Coaxial Connections
- Crosshatched Ground: How Patterning Affects Imedance and Crosstalk
Chapter 5: Clock-Related Noise Issues
- Unexpected Synchronization Difficulties
- Do Terminations Reduce Emissions?
- Common and Differential Modes
- Clock Jitter - Causes and Solutions
- Examples Jitter Measurements
Chapter 6: Connectors
- Board-to-board Connector Electrical Noise Performance
- Importance of Connector Grounding
- Example: Film Showing Measurment of Connector Performance
Chapter 7: System Test
- Compliance Testing: An Interview with JP Miller, distinguished technologist at Hewlett Packard.
- Debugging: Tips from David Agans
- Special Signals: Measuring Extremely Low Distortion
- Special Signals: Dealing with Large Amplitudes
- Personnel Issues
- Practical System-Design Advice (Wrap-up)
Who has participated in this workshop?
Originally developed for the clients in the military/avionics space, this workshop has been presented by Dr. Johnson for thousands of engineers in both public and private forums worldwide. Past participants represent a wide variety of organizations, including:
|Who Has Participated|
|Cisco Systems||L-3 Comm.||Rohde & Schwarz|
|Dell Computer||Lockheed Martin||Samsung|
|Ericsson||Mentor Graphics||Sandia National Labs|
|Harris Corp.||Motorola||Texas Instruments|
|Hewlett-Packard||NASA||US Naval Warfare Systems|