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HDMI 2.1: How it Became the Most Popular Display Interface

HDMI (High-Definition Multimedia Interface) is a proprietary audio/video interface for transferring uncompressed video data and compressed or uncompressed digital audio data from an HDMI-compliant source device, such as a display controller, to a compatible computer monitor, video projector, digital television, or digital audio device. HDMI is a digital replacement for analog video standards, represented using one of several luminance/color-difference color spaces. We introduced HDMI 2.1 in our previous blog – HDMI 2.1: Channeling the GenX Audio Video Experience. In this blog we will discuss about evolution and key features of HDMI from v1.4 to v2.1.

HDMI has 3 physically separate communication channels:

  • DDC (Display Data Channel) is a simple communication channel based on the I2C spec that enables the display to communicate its supported display modes and enable the host to adjust parameters such as brightness and contrast.
  • TMDS (Transition Minimized Differential Signaling) interleaves audio, video, and auxiliary data. During the video data period, the pixels of an active video line are transmitted; and during the horizontal and vertical blanking intervals, audio and auxiliary data are transmitted within a series of packets. The control period occurs between video and data island periods.
  • CEC (Consumer Electronics Control) allows the user to control up-to ten enabled devices connected through HDMI.

HDMI 1.4 added 2 additional channels:

  • ARC (Audio Return Channel) is an audio link meant to replace other audio cables between for example the TV and a speaker system.
  • HEC (HDMI Ethernet Channel) provides a 100Mbit/s bi-directional link.

Content protection is provided through HDCP (High-bandwidth Digital Content Protection). HDMI can use HDCP to encrypt the signal if required by the source device.

Frame line to packet transmission

HDMI 1.4b supports the TMDS character rate for up to 340Mcsc; HDMI 2.0 adds the TMDS signals at TMDS character rate from 340 to 600 Mcsc and adds scrambling for EMI/RFI at all TMDS character rates. For TMDS character rates above 340 Mcsc, the TMDS clock rate will be one fourth (1/4) of the TMDS character rate. The TMDS bit rate remains at 10 times the TMDS character rate, and is therefore 40 times the TMDS clock rate. For TMDS character rates at or below 340 Mcsc, the TMDS clock rate is equal to the TMDS character rate, and the TMDS bit rate is equal to 10 times TMDS clock rate. The Source shall not transmit at TMDS character rates higher than the maximum rate supported by the Sink device. With the introduction of HDMI 2.1, the user has the capability to transfer data at a fixed rate with maximum link bit rate supported of 12Gbps on 4 lanes. In HDMI 2.0 support for HDR video transport was added by including an extension of the static metadata signaling, whereas HDMI 2.1 also adds support of dynamic metadata. The table below lists the basic difference between HDMI 1.4, 2.0 and 2.1.

HDMI has evolved as the most popular display interface. There have been significant improvements from HDMI v1.4 to v2.1 in terms of speed, data integrity, mode of data transmission, etc. Stay tuned for our upcoming blogs on data transport and scrambling in HDMI 2.0. Synopsys VIP for HDMI supports HDMI1.4, HDMI 2.0, HDMI 2.1, HDCP 1.4, HDCP 2.2 and DSC 1.2. Read about Novatek’s adoption of Synopsys’ industry first VIP and source code Test Suite for HDMI 2.1 and HDCP 2.2 to design their next-generation multimedia chips. Also read our previous blog – HDMI 2.1: Channeling the GenX Audio Video Experience, and white paper on DSC – Analyzing the Losses in Visually Lossless Compression Algorithm.

Authored by Snigdha Dua