Effortless Circuit Design with a Hierarchical Schematic System

 

Introduction

Schematics provide the critical visual representation of electrical connectivity and hierarchy in electronic systems. For anything beyond trivial circuits, monolithic flat schematics quickly become an unmanageable tangle of wires and symbols. This impedes comprehension, editing, and reuse. Hierarchical schematic design methodologies solve these problems by dividing systems into logical functional blocks with clean interfaces. This article explores essential capabilities of modern hierarchical EDA tools that remove complexity barriers and accelerate circuit creation.

Hierarchy Concepts

Hierarchical design applies the "divide and conquer" principle to tame complex schematics through abstraction and modularity:

• Partition system into smaller functional blocks
• Encapsulate blocks as high-level symbols
• Create connectivity at top level
• Repeat process recursively

This provides major benefits:

• Improved comprehension
• Logical editing at each level
• Reuse of common blocks
• Team-based design
• Automated documentation
• Synchronized PCB layout
• Reduced errors

With proper EDA tool support, hierarchy transforms chaotic schematics into well-organized systems.

Core Capabilities

Effective hierarchy requires specialized EDA capabilities:

Top-down/bottom-up design - Flexibly edit subcircuits and high-level diagrams

Unlimited hierarchy - No restrictions on number of levels

Custom symbols - User-defined representations for hierarchical blocks

Template circuits - Save common circuits as reuse snippets

Forward/back annotation - Changes percolate up/down automatically

Bus support - Maintain signal groups across hierarchy

Cross-probing - Click symbols to visually navigate hierarchy

Flatten/expand - Temporary view high-level netlist or expand hierarchy

Automated documentation - Reports, netlists, BoMs handle hierarchy

Let's examine these in detail.

Top-Down and Bottom-Up Workflow

Hierarchy requires both top-down and bottom-up design ability:

Top-down - Divide a high-level system into sub-blocks first, then design internals

Bottom-up - Design low-level subcircuits first, then integrate into top level

This bi-directional approach provides flexibility:

• Quickly mockup overall system architecture from libraries
• Incrementally flesh out details of each functional block
• Develop and reuse common circuits like power, I/O, control
• Incorporate existing schematics as new subsystems

Top editors support entry at all levels of hierarchy rather than forcing strictly linear progression.

Unlimited Levels of Hierarchy

Hierarchies must scale to handle systems of any complexity. Key capabilities include:

• No hard limits on nesting depth
• No performance degradation with deep trees
• Streamlined navigation through multi-level hierarchy
• Flexible coloring/numbering of symbols
• Automatic alignment and grouping
• Expand/collapse selective branches

With unlimited hierarchy, users can architect systems at the most appropriate levels of abstraction without tool limitations.

Customizable Hierarchical Block Symbols

Representing nested schematics by generic subcircuit symbols has drawbacks:

• All symbols look identical
• No visual cue of contents and I/O
• Difficult to disambiguate symbols

Advanced EDA tools allow designing custom hierarchical symbols:

• Unique shapes, color fills, text
• Graphical depiction of internal circuitry
• Visible terminals for external connections
• Dynamic update when edited

Intelligent custom symbols make hierarchical schematics far easier to visualize at a glance.

Circuit Snippets Enable Reuse

Engineers frequently reuse standard subcircuits across projects. Template snippets streamline reuse:

• Save commonly used subcircuits as standalone objects
• Organize snippets into searchable libraries
• Drag-drop into new designs
• Modify parameters and I/O
• Propagate changes to instances
• Build company IP repositories

Circuit reuse eliminates reinventing redundant blocks every project.

Automatic Back-Annotation

A major challenge with hierarchy is propagating changes. Automated tools simplify this flow:

Bottom-up annotation - Subcircuit changes flow upward through the hierarchy

• Component edits reflected in symbols
• New external connections added
• Parameter value updates

Top-down annotation

• High-level edits push downward
• Component substitutions permeate downward
• Net name edits change globally
• Color schemes cascade

Bi-directional annotation keeps all hierarchy levels in sync without tedious manual bookkeeping.

Bus Support

Buses (signal groups) are essential for hierarchical designs. Key capabilities include:

• Logical signal bundles to simplify interfaces
• Create any bus width
• Re-order, add, remove wires
• Vector/array-style access to members
• Expand to individual nets as needed
• Sync bus structure between symbols
• Cross-hierarchy bus continuity

Buses abstract and group related signals to reduce connections clutter.

Hierarchy Navigation and Visualization

Navigating multi-level schematics requires specialized UIs:

• Hierarchy pane - tree/list shows circuit structure
• Search/filter to quickly find blocks
• Cross probe by clicking symbols to visualize connectivity
• Colouring to highlight context
• Zoom controls - global or selective views
• Bird's eye navigator window
• Collapse/expand selective branches
• Temporary flattening into netlist view

Advanced navigation aids comprehension of complex hierarchies and speeds editing.

Integrated Documentation

Hierarchies create challenges for system documentation. Smart tools automate reporting:

• Hierarchy-aware netlist extraction
• Visual bounding-box BOMs
• Drill-down cross reference
• Obfuscated black-box views
• Flexible template-based reporting
• Versioning/compare utilities

Full hierarchy support in documentation outputs enables one-click automated reports.

Design Synchronization

For efficient PCB layout, EDA tools must integrate schematic-PCB synchronization:

Hierarchy mapping - Mirror structure between tools

Netlist extractions - Multi-sheet, multi-level netlists

Incremental changes - Limited update for local edits

Pin swapping - Allow port rearrangement

Block padding - Maintain spacing when flattening

Design partitioning - Slice hierarchy for layout

Maintaining hierarchy during PCB design synchronization eliminates scrap and rework.

Team Enablement

Collaboration features are essential for large hierarchical designs:

• Concurrent multi-user editing
• Prescribed workflows
• Change awareness
• Task assignments
• User permissions
• Revision control
• Release management

Smooth teamwork prevents disjointed, redundant work and speeds complex projects.

Conclusion

Hierarchies transform chaotic schematics into well-architected systems by applying divide-and-conquer principles. Leading EDA tools make hierarchical design effortless through capabilities like unlimited abstraction, mixed top-down and bottom-up entry, custom symbols, reuse templates, annotation synchronization, navigation aids, and integrated documentation. By leveraging hierarchy, engineers can confidently conquer ever-increasing circuit complexity.

Frequently Asked Questions

What techniques help determine optimal hierarchical partitioning of a complex schematic?

Look for functional blocks like clocking circuits, power systems, serial buses, and peripheral interfaces that have defined inputs/outputs and internal cohesion. Analyze connectivity between sections to identify clear separation points. Review pacing of design tasks and team assignments.

How many hierarchy levels is too many? Is there a point of diminishing returns?

There is no definitive limit. More levels increase comprehension but reduce visibility. A heuristic is to continue decomposing a system until each block fits comfortably on one screen. Test if further decomposition starts feeling excessive. The optimal depth depends on the specific design.

What are some warning signs that our current EDA tools do not support effective hierarchical design?

Symptoms include copy-paste duplication rather than reuse, reluctance to create hierarchy, flatten operations required before PCB layout, manual change propagation, inability to cross-probe between hierarchy levels, lack of overview visualization tools, and difficulty reporting across hierarchy.

How can designers improve the clarity and readability of complex hierarchical schematics?

Use visual cues like color-coded modules with defined signal flow "lanes", typographic emphasis and white space for hierarchy, judicious abbreviations, descriptive custom symbols, visual demarcation of circuit domains, connection dot patterns, and selective background watermarks.

What skills should engineers learn to become proficient using hierarchical EDA?

Key competencies are modular thinking, clean interface design, visual abstraction, change impact analysis, design documentation skills, team communication protocols, version control fluency, and mastery of tool features for hierarchy navigation, annotation, reporting, and reuse.