Similarity Logic

Logic IC Similarity Calculator Skill

Guidance for working with LogicICSimilarityCalculator in the lib-electronic-components library.

For metadata-driven similarity architecture, see /similarity-metadata:

• SpecImportance levels (CRITICAL, HIGH, MEDIUM, LOW, OPTIONAL)
• ToleranceRule types (exactMatch, percentageTolerance, minimumRequired, etc.)
• SimilarityProfile contexts (DESIGN_PHASE, REPLACEMENT, COST_OPTIMIZATION, etc.)
• Calculator integration patterns and gotchas

Overview

The LogicICSimilarityCalculator compares logic ICs based on:

• Logic function - NAND, NOR, NOT, AND, OR, flip-flops, etc.
• Technology family - LS, ALS, HC, HCT, F, etc.
• Part number series - 74xx vs CD4000

Applicable Types

ComponentType.LOGIC_IC
ComponentType.LOGIC_IC_NEXPERIA
ComponentType.LOGIC_IC_DIODES
ComponentType.IC  // Generic IC type also supported

Returns false for null type.

Similarity Thresholds

HIGH_SIMILARITY = 0.9;   // Same function, compatible technology
MEDIUM_SIMILARITY = 0.5; // Related parts
LOW_SIMILARITY = 0.3;    // Different functions

74xx Series

Technology Families (Interchangeable within groups)

// Compatible technologies = HIGH
calculator.calculateSimilarity("74LS00", "74HC00", registry);
// Returns 0.9

calculator.calculateSimilarity("74LS04", "74ALS04", registry);
// Returns 0.9

Function Groups

// Different functions = LOW
calculator.calculateSimilarity("74LS00", "74LS74", registry);
// Returns 0.3 (NAND vs Flip-Flop)

CD4000 CMOS Series

Common CD4000 Parts

CD4000 Package Codes

// Same CD4000 IC, different package = HIGH
calculator.calculateSimilarity("CD4001BE", "CD4001BM", registry);
// Returns 0.9

// Different CD4000 ICs = LOW
calculator.calculateSimilarity("CD4001BE", "CD4011BE", registry);
// Returns 0.3

Cross-Series Comparison

74xx and CD4000 are generally not interchangeable:

// 74xx vs CD4000 with same function
calculator.calculateSimilarity("74HC00", "CD4011BE", registry);
// Returns LOW (different series, even if same function)

Test Examples

// Same 74xx, compatible technologies
calculator.calculateSimilarity("74LS00", "74HC00", registry);
// Returns 0.9

// Same CD4000 IC, different package
calculator.calculateSimilarity("CD4001BE", "CD4001BM", registry);
// Returns 0.9

// Same function group in 74xx
calculator.calculateSimilarity("74LS04", "74ALS04", registry);
// Returns 0.9

// Different functions
calculator.calculateSimilarity("74LS00", "74LS74", registry);
// Returns 0.3

Learnings & Quirks

74xx Part Number Structure

74 LS 04 N
│  │  │  │
│  │  │  └── Package (N=DIP)
│  │  └───── Function (04=Inverter)
│  └──────── Technology (LS=Low-power Schottky)
└─────────── Series prefix

CD4000 Part Number Structure

CD 4001 BE
│  │    │
│  │    └── Package (BE=Plastic DIP)
│  └─────── Function number
└────────── Series prefix

Metadata-Driven Implementation (January 2026)

Status: ✅ Converted (PR #119)

The LogicICSimilarityCalculator now uses a metadata-driven approach with spec-based comparison.

Specs Compared

Implementation Pattern

// Short-circuit check for CRITICAL incompatibility
if (!function1.isEmpty() && !function2.isEmpty() && !areSameFunction(mpn1, mpn2)) {
    return LOW_SIMILARITY;
}

// Short-circuit for series incompatibility (74xx vs CD4000)
if (!series1.isEmpty() && !series2.isEmpty() && !series1.equals(series2)) {
    return 0.0;
}

// Extract function from both 74xx and CD4000 series
private String extractFunction(String mpn) {
    if (mpn.matches("^CD4.*")) {
        // CD4001 → "001", CD4011 → "011"
        return cmosPatternMatcher.group(1);
    }
    // 74LS00 → "00", 74HC138 → "138"
    return ttlPatternMatcher.group(3);
}

Behavior Changes

Why more accurate: Metadata approach correctly handles both 74xx and CD4000 series, with series check preventing false matches.

Technology Compatibility Notes

• HC is CMOS, LS is TTL - but they're voltage compatible at 5V
• HCT is specifically designed for TTL compatibility
• 74LVC series is for 3.3V operation

Function Group Patterns

• The 2-digit function number after technology code determines function
• Same function number = same function across technologies