HDMI (High-Definition Multimedia Interface) is one of the primary interfaces for modern audiovisual transmission, widely used across devices such as TVs, monitors, graphics cards, sound systems, and game consoles. While its external form factor has remained largely unchanged for over a decade, did you know that HDMI's internal structure has undergone significant, yet subtle, transformations with each new version?

This article takes you through the structural differences within the HDMI 1.4, 2.0, and 2.1 interfaces, offering a true understanding of "What is in an HDMI cable."

1. Structural Overview of the Standard HDMI Interface

The standard-sized HDMI Type-A connector (common on TVs, monitors, GPUs, etc.) features a total of 19 pins, arranged in two rows. These pins primarily transmit:

TMDS differential data (Video/Audio)

Clock signal

Power and Ground

Control channels (e.g., CEC, DDC)

Hot Plug Detect

Below is a simplified structural diagram illustrating the basic HDMI Type-A pinout:

HEAC Table 2-5 Type A-to-Type A Cable Wire Assignment

2. HDMI 1.4 and Earlier: The Structural Foundation Era

Representative Year: 2009 and prior

Internal Structural Characteristics:

Utilized 3 TMDS differential channels, each with a maximum bandwidth of 3.4 Gbps.

No change in physical pin count; maintained the 19-pin design.

Audio, video, clock, and control signals all routed through these 19 pins.

Typical internal cable construction:

• 3 pairs of differential data lines (TMDS)

• 1 pair of differential clock lines

• Control lines (CEC/DDC, etc.)

• Shielding layer + Ground layer

Cable Structure:

Engineering Practice:

• HDMI 1.4 cables typically use 28AWG to 30AWG copper conductors.

• Simple shielding structure, primarily braiding + aluminum foil.

• Cable length is generally not recommended beyond 5 meters to avoid signal degradation.

3. HDMI 2.0: Performance Boost, Structurally Conservative

Representative Year: 2013

Internal Structural Changes:

Still utilized 3 TMDS data lanes, but increased signal frequency to 6 Gbps per channel.

Pin count remained unchanged at 19 pins.

Introduced support for dual video streams, BT.2020 color space, and high-sample-rate audio primarily through increased signal rates, not structural changes.

Engineering Practice:

To accommodate higher bandwidth, HDMI 2.0 cables commonly use 28AWG to 26AWG conductors.

Required improved shielding: Double-layer aluminum foil + high-density braiding.

Connectors often incorporate ferrite cores (chokes) and enhanced grounding to reduce EMI.

Summary:

HDMI 2.0's core change was increased speed, not structure.

The same 19-pin structure achieved enhanced capabilities through higher frequencies.

4. HDMI 2.1: A Major Physical and Structural Evolution

Representative Year: 2017

Significant Internal Structural Changes:

• Transition from TMDS to FRL Architecture

FRL (Fixed Rate Link) technology replaced traditional TMDS, employing 4 FRL differential lanes capable of up to 12 Gbps per lane.

Bandwidth doubled significantly, while still utilizing the original 19-pin physical structure.

• Pin Functionality Logically Reassigned in FRL Mode (Physical Pins Unchanged)

The original clock pair was repurposed as an FRL lane or auxiliary channel.

Functionality of several pins automatically switched based on whether FRL or TMDS mode was active.

• Connector Structure Unchanged, Cable Internals Revolutionized

Extremely demanding cable requirements: low latency, low crosstalk, high shielding effectiveness.

Premium certified cables are labeled "Ultra High Speed HDMI Cable", guaranteeing support for 48Gbps.

• Engineering Practice:

Typically employed 26AWG or thicker conductors.

Typical construction: 4 individually shielded differential pairs, triple-layer composite shielding (braid + foil + conductive layer), low-dielectric-constant insulation.

Reinforced connectors: Gold plating thickness increased to 15μm, integrated EMI filtering ferrites, contact pin pressure increased by 30%.

5. Structural Comparison Summary Table

6. How Did Performance Multiply Without Structural Change?

This represents an engineering "magic trick" in HDMI's design:

Performance leaps were achieved by increasing signal rates, optimizing the protocol structure (e.g., FRL), and refining internal cable shielding and conductor layout – all without altering the physical connector.

This explains why:

HDMI ports look identical, but cables are not universally compatible.

HDMI cable prices range dramatically from a few dollars to hundreds, as structural quality determines the performance ceiling.

7. Final Thoughts

As a consumer AV interface standard, HDMI's stable exterior conceals significant technological evolution. For consumers, choosing a cable supporting the 2.1 specification isn't just about "supporting 8K"; it's crucial to ensure its internal structure genuinely meets the certification requirements – effective shielding, quality conductors, and FRL compatibility are all indispensable.

Tag：HDMI,HDMI Cable