AN 958: Board Design Guidelines

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ID 683073
Date 6/26/2023
Public
Document Table of Contents
Document Table of Contents x
1. Power Distribution Network 2. Gigahertz Channel Design Considerations 3. PCB and Stack-Up Design Considerations 4. Device Pin-Map, Checklists, and Connection Guidelines 5. General Board Design Considerations/Guidelines 6. Memory Interfacing Guidelines 7. Power Dissipation and Thermal Management 8. Tools, Models, and Libraries 9. Reference Designs and Development Kits 10. Document Revision History for AN 958: Board Design Guidelines
1. Power Distribution Network x
1.1. Target Impedance Decoupling Method 1.2. Voltage Regulator Selection 1.3. PDN Design Tool 1.4. Plane Capacitance 1.5. Minimization Parasitic Inductances 1.6. Additional Resources
1.1. Target Impedance Decoupling Method x
1.1.1. FDTIM Decoupling Concepts 1.1.2. Select Decoupling CAPS to Meet ZTARGET
1.1.1. FDTIM Decoupling Concepts x
1.1.1.1. Determining the ZTARGET 1.1.1.2. Determining the fTARGET
1.5. Minimization Parasitic Inductances x
1.5.1. VRM 1.5.2. Decaps 1.5.3. Mounting Inductance 1.5.4. Spreading Inductance 1.5.5. Inter-Plane Capacitance 1.5.6. Conclusion
2. Gigahertz Channel Design Considerations x
2.1. Material Selection and Loss 2.2. Routing Guidelines for Gigabit Channel Designs 2.3. Minimizing Adverse Effects of Material Glass Fiber Weaves 2.4. Plane Cut-outs Below Surface Mount Pads 2.5. Transmitter Pre-Emphasis and Receiver Equalization 2.6. Additional Resources
2.2. Routing Guidelines for Gigabit Channel Designs x
2.2.1. Via Optimization Techniques
2.2.1. Via Optimization Techniques x
2.2.1.1. General Routing Guidelines
3. PCB and Stack-Up Design Considerations x
3.1. Material Selection and Loss 3.2. Board Thickness and Vias 3.3. PCB Recommended Layout Footprint Land Pattern
4. Device Pin-Map, Checklists, and Connection Guidelines x
4.1. High Speed Board Design Advisor 4.2. Complete Pin Connection Table by Device 4.3. Pin Connection Guidelines By Device 4.4. Design for Debug with JTAG Pins 4.5. Hot Socketing, POR and Power Sequencing Support 4.6. Implementing OCT 4.7. Unused I/O Pins Guidelines 4.8. Device Breakout Guidelines 4.9. Additional Resources
5. General Board Design Considerations/Guidelines x
5.1. Board Design Process Overview 5.2. Design Security Features in FPGAs 5.3. EMI 5.4. Discrete Component Selection for High-Speed Design 5.5. S-Parameters 5.6. Smith Chart 5.7. AC Versus DC Coupling 5.8. Additional Resources
5.1. Board Design Process Overview x
5.1.1. Material Selection and Loss 5.1.2. Cross Talk Minimization 5.1.3. Power Filtering/Distribution 5.1.4. Unused I/O Pins 5.1.5. Signal Trace Routing 5.1.6. Ground Bounce 5.1.7. Understanding Transmission Lines 5.1.8. Impedance Calculation 5.1.9. Coplanar Wave Guides 5.1.10. Simultaneous Switching Noise Guidelines
5.1.3. Power Filtering/Distribution x
5.1.3.1. Filtering Noise 5.1.3.2. Distributing Power
5.1.5. Signal Trace Routing x
5.1.5.1. Single Ended Trace Routing 5.1.5.2. Differential Trace Routing 5.1.5.3. Skew Minimization 5.1.5.4. Termination Schemes 5.1.5.5. Termination Design Example 5.1.5.6. Discontinuities Related to a Transmission Path
5.1.5.4. Termination Schemes x
5.1.5.4.1. Simple Parallel Termination 5.1.5.4.2. Thevenin Parallel Termination 5.1.5.4.3. Active Parallel Termination 5.1.5.4.4. Series-RC Parallel Termination 5.1.5.4.5. Series Termination 5.1.5.4.6. Differential Pair Termination 5.1.5.4.7. On-Chip Termination
5.1.5.5. Termination Design Example x
5.1.5.5.1. Determine the Delay 5.1.5.5.2. Determine the Bandwidth 5.1.5.5.3. Using Series Termination 5.1.5.5.4. Using Parallel Termination
5.1.5.6. Discontinuities Related to a Transmission Path x
5.1.5.6.1. Inductive Discontinuity 5.1.5.6.2. Capacitive Discontinuity 5.1.5.6.3. Via Discontinuity 5.1.5.6.4. Right-Angle Bends Related to a Transmission Path
5.1.6. Ground Bounce x
5.1.6.1. Design Guidelines 5.1.6.2. Analyzing Ground Bounce 5.1.6.3. Switching Outputs 5.1.6.4. Quiet Outputs 5.1.6.5. Minimizing Lead Inductance
5.1.8. Impedance Calculation x
5.1.8.1. Microstrip Impedance 5.1.8.2. Stripline Impedance 5.1.8.3. Propagation Delay
5.1.8.3. Propagation Delay x
5.1.8.3.1. Microstrip Layout Propagation Delay 5.1.8.3.2. Stripline Layout Propagation Delay
5.1.9. Coplanar Wave Guides x
5.1.9.1. Simple Coplanar Wave Guide 5.1.9.2. Grounded Coplanar Wave Guide 5.1.9.3. Grounded Differential Coplanar Wave Guide
5.4. Discrete Component Selection for High-Speed Design x
5.4.1. Resistors and Capacitors 5.4.2. Inductors and Ferrite Beads 5.4.3. SMA Connectors
6. Memory Interfacing Guidelines x
6.1. DDR3 Board Design Guidelines 6.2. DDR2 Board Design Guidelines 6.3. DDR Board Design Guidelines 6.4. QDR II and QDR II+ 6.5. RLDRAM II 6.6. Additional Resources
7. Power Dissipation and Thermal Management x
7.1. Power Management Guidelines 7.2. Heat Sinking and Thermal Managment for FPGAs 7.3. Additional Resources
8. Tools, Models, and Libraries x
8.1. Design Tools 8.2. I/O Buffer Models 8.3. Device Libraries 8.4. Net Length Reports 8.5. Thermal Models
9. Reference Designs and Development Kits x
9.1. Development Kits
1. Power Distribution Network
2. Gigahertz Channel Design Considerations
3. PCB and Stack-Up Design Considerations
4. Device Pin-Map, Checklists, and Connection Guidelines
5. General Board Design Considerations/Guidelines
6. Memory Interfacing Guidelines
7. Power Dissipation and Thermal Management
8. Tools, Models, and Libraries
9. Reference Designs and Development Kits
10. Document Revision History for AN 958: Board Design Guidelines

5.1.5.4.2. Thevenin Parallel Termination

An alternative parallel termination scheme uses a Thevenin voltage divider (refer to Figure 31). The terminating resistor is split between R1 and R2, which equals the line impedance when combined. Although this scheme reduces the current drawn from the source device, it adds current drawn from the power supply because the resistors are tied between VCC and GND.

Figure 31. Thevenin Termination

Stub length is dependent on signal rise and fall time and should be kept to a minimum. If your design requires a long termination line between the terminator and receiver, use fly-by termination or Thevenin fly-by termination. Refer to Figure 31 and Figure 32.

Figure 32. Thevenin Fly-By Termination
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