HDMI Clock Cleaning for Lower DAC Jitter and Audio Distortion
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Solution Overview
Problem
Conventional HDMI systems suffer from audio distortion due to jitter on the TMDS clock signal being aliased into the audible frequency range, making it impractical to reduce phase noise without introducing significant noise or jitter.
Innovation Solution
A clock cleaning device, such as a Phase-Locked Loop (PLL) with an overclocked Voltage-Controlled Oscillator (VCO), is strategically placed in the signal path to reduce jitter on the TMDS clock before it aliases to a low frequency, using a higher frequency low-pass filter to minimize additional noise introduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a clock cleaning device is placed in the HDMI signal path to reduce jitter on the TMDS clock signal, then audio fidelity is improved, but device complexity increases
Solution Approach 1:
A clock cleaning device is introduced as an intermediary component in the HDMI signal path between the source and sink. This device receives the TMDS clock signal, cleans it by reducing jitter through a phase-locked loop (PLL) circuit, and outputs a cleaned clock signal. The intermediary device isolates the jitter problem from the audio processing path without requiring modification to existing HDMI equipment, thus improving audio fidelity while adding minimal complexity.
2Reliability
If jitter reduction is attempted at low frequencies after aliasing occurs, then phase noise can be reduced, but the filtering becomes impractical due to excessive noise and jitter introduction
Solution Approach 1:
The clock cleaning device performs jitter reduction on the TMDS clock signal before it is divided down to lower frequencies in the audio processing path. By cleaning the clock at its original higher frequency (25-340 MHz range), the system prevents jitter aliasing into the audible frequency range in the first place. This preliminary action makes the filtering task practical and effective, as high-frequency jitter can be filtered more easily than low-frequency jitter that has already aliased into the audio band.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces jitter on the audio DAC clock, improving audio fidelity by maintaining lower harmonic distortion and ensuring higher quality audio transmission.
Implementation Method 1
A clock cleaning device, such as a Phase-Locked Loop (PLL) with an overclocked Voltage-Controlled Oscillator (VCO), is strategically placed in the signal path to reduce jitter on the TMDS clock
Implementation Method 2
A clock cleaning device, such as a Phase-Locked Loop (PLL) with an overclocked Voltage-Controlled Oscillator (VCO), is strategically placed in the signal path
Implementation Method 3
using a higher frequency low-pass filter to minimize additional noise introduction
Data Source
AI summary
HDMI is a digital audio and video communications protocol commonly used in consumer electronics. HDMI is particularly synonymous with high fidelity audio and video. Even though HDMI is a digital communications protocol, the audio quality can be impaired by analog signal impairments and distortions even if there are no digital decoding errors. In particular, the very process by which the audio is converted from Digital (HDMI) to human audible “Analog Audio” can be prone to errors. This occurs when the Digital to Analog Converter (DAC) clock, which is derived from the HDMI TMDS clock or HDMI source, is “distorted” due to its jitter, resulting in erroneous sampling or outputting of vital audio samples, thereby reducing the audio quality of the experience. The present invention reduces the jitter on the TMDS clock, and hence the audio DAC clock, resulting in lower audio distortion. Exemplary simple embodiments of the present invention in an HDMI cable can dramatically improve audio fidelity in existing home entertainment systems without an upgrade to expensive major equipment replacement such as the source (audio system) or sink (Television).