TSP #256 - Mysteries of Optical HDMI Cables - Tutorial, Teardown & Analysis of Inexpensive Optics
In this episode, Shahriar takes an in-depth look at the design and architecture of optical HDMI cables, which significantly extend the reach of traditional HDMI 2.0 twisted-pair copper links at a low cost.
The fundamentals of HDMI high-speed data transmission are explored, with a focus on the TMDS (Transition Minimized Differential Signaling) standard. The challenges of transitioning from twisted pairs to optical lanes are examined, highlighting the role of VCSELs and PIN photodiodes. Optical modules are analyzed in detail, emphasizing free-space optics and optical confinement techniques used with lasers and detectors. The received high-speed lane’s eye diagram is captured, and the VCSELs’ optical wavelength is confirmed to be 850 nm.
Additionally, the TX (driver) and RX (TIALA) chips are inspected under a microscope, revealing the VCSEL and photodetector arrays. The overall electronic architecture is then discussed in greater detail.
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