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From TMDS to Thunderbolt and

Everything In Between

The phrase “digital video” is ubiquitous, but seldom defined. What makes it digital? What are the rules for converting formats? Let’s find out…

Digital Video

Formats

Joseph D. Cornwall, CTS-D

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“AN EDUCATION ISN'T HOW MUCH YOU HAVE

COMMITTED TO MEMORY, OR EVEN HOW MUCH

YOU KNOW. IT'S BEING ABLE TO DIFFERENTIATE

BETWEEN WHAT YOU DO KNOW AND WHAT YOU

DON'T.”

- JACQUES ANATOLE FRANCOIS THIBAULT

Welcome To Today’s Presentation:

Understanding Digital Video Formats

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Our Agenda

• Define digital

─ What are the elements of a digital signal?

• Digital Rights Management

• DisplayID

─ What is a DDC? Where’s the EDID?

• TMDS explained

• Digital Visual Interface DVI

• High Definition Multimedia Interface HDMI

• DisplayPort

• Thunderbolt

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“Any sufficiently advanced technology is indistinguishable from magic.”

─ Arthur C. Clarke

Define “Digital”

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The Elements of a Video Signal

• RGB additive color model

divides a video signal into

3 ”components”

─ RGB or YPbPr (YCbCr)

• Bandwidth is directly

proportional to visual detail

─ In analog systems, the ability to

pass higher frequencies equates to

the ability to display finer detail

• Amplitude is directly

proportional to color

saturation

a

m

p

l

i

t

u

d

e

time

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The Numbers Behind The Bits-

Understanding Sampling

Analog signals are continuous

in time

─ All waveforms consist of fundamental

sine waves plus harmonics

Shannon-Nyquist says > 2

samples are necessary to

recreate a waveform

• Resolution is bound by

sampling rate

─ Aliasing occurs when input frequency

exceeds 2x sampling frequency

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The Numbers Behind The Bits-

Making Sense of Bit Depth

• 3 bits = 2 x 2 x 2 = 8 total

possible values, for example

• Each bit represents a step in

voltage

• Values that fall between

“steps” are lost information

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“Obviously crime pays, or there'd be no crime.”

─ G. Gordon Liddy

Digital Rights Management

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HDCP

• High Bandwidth Digital Content

Protection

─ Because in the digital world there are

no copies, only clones

• Blom's Scheme is a symmetric

threshold key exchange protocol

used in cryptography

─ A trusted party gives each participant a

secret key and a public identifier, which

enables any two participants to

independently create a shared key for

communicating.

─ Keys updated after each encoded

frame

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Inside HDCP

•HDCP makes use of a three-stage content

protection process

─ Device authentication and key exchange

─ Encryption of content

─ Key-revocation procedures

•Unique keys are assigned to each device

─ Consists of up to 40 different 'secret or private'

keys, each 56 bits long, embedded in the device

─ For each set of keys, a special public key, called a

“key selection vector”, is created

─ ‘Combining’ an embedded key with a public key

creates a temporary session key, allowing for clear

communication between the devices

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“If you're not scared or angry at the thought of a human brain being

controlled remotely, then it could be this prototype of mine is finally

starting to work.”

- John Alejandro King

Telling the Monitor What to Expect

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DDC, EDID and DisplayID

• Display Data Channel

• Extended Display Identification Data

• DisplayID 1.3 (2013) is the most current iteration

─ Enables the display (sink) to communicate supported display modes to the source via a compact binary file format that describes the monitor's capabilities and supported graphics modes

─ Stored in a read-only memory chip programmed by the manufacturer of the monitor

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“All truths are easy to understand

once they are discovered; the point

is to discover them.”

- Galileo Galilei

Making Signals Easier To Transport

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Transition Minimized Differential Signaling

• TMDS is a two-stage process

that converts a signal from

parallel to serial and adds

additional bits to balance DC

• Makes signals smaller by

converting them from 8 bit to 10

bit

─ 8b/10b line coding - 8-bit data plus

2 bits of control signals

─ 4 channels: red, green, blue, clock

─ Twisted pair for noise reduction

─ Current mode logic (CML), DC

coupled and terminated to 3.3 volts

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The TMDS Algorithm

• TMDS adds a 9th bit to the

digital word to “minimize” the

transitions from digital ones to

digital zeros

─ This decreases high frequency content

making the signal more robust and

easier to transport

• The algorithm then adds a 10th

bit to provide for DC balancing

─ DC balancing inverts the digital word so

the signal has an equal number of zeros

and ones

─ Provides a stable, predictable signal to

the differential amplifiers

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“I HAVE YET TO SEE ANY PROBLEM,

HOWEVER COMPLICATED, WHICH, WHEN

YOU LOOKED AT IT IN THE RIGHT WAY, DID

NOT BECOME STILL MORE COMPLICATED.”

POUL ANDERSON

Typical Signal Flow

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“To manage a system effectively, you might focus on the interactions

of the parts rather than their behavior taken separately.”

─ Russell l. Ackoff

Putting It All Together

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Digital Visual Interface - DVI

R RG G

BB S S

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In December 2010, Intel, AMD, and several computer and

display manufacturers announced they would stop

supporting DVI-I, VGA and LVDS-technologies by 2015.

These will be replaced by DisplayPort and HDMI.

"Legacy interfaces such as VGA, DVI and LVDS have not

kept pace, and newer standards such as DisplayPort

and HDMI clearly provide the best connectivity options

moving forward. In our opinion, DisplayPort 1.2 is the

future interface for PC monitors, along with HDMI 1.4a

for TV connectivity".

Are DVI Connections Obsolete?

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High Definition Multimedia Interface

RR

G G

B B

S SC

EC

DD

CD

DC

DD

CH

EA

C

+5V

HP

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HDMI(e) HEAC

HEAC is the HDMI Ethernet and

Audio-return Channel and

supports up to 100Mbits data

transfer. Signal selection is

excusive.

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HDMI 2.0 Features and Upgrades

UltraHD and 4K Video

Support

Increase bandwidth

from 10.2 to 18 Gbps

Noise Reduction

System For TMDS

Lanes

Support for additional

color space formats

including 4:2:0

Up To 21:9 Aspect Ratio

Support

Multi-stream Video

Capable (MST)

CEC 2.0 Error correction

Improved audio ability

with support to 32

channels

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SDI - Serial Digital Interface

• SDI (1989)

• HD SDI (1998)

• 3G SDI (2006)• 3 Gbit/s and 1080p

• 16 Channels of embedded audio

• 6G SDI

• 6 Gbit/s and 4Kp30

• 12G SDI

• 12 Gbit/s and 4Kp60

• 24G SDI

• 24Gbit/s and 8Kp60

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DisplayPort

Au

x

Lan

e 0

Lan

e 2

Lan

e 1

Lan

e 3

Ho

t P

lug

HP

Ret

Po

wer

Co

nfi

g

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DisplayPort Tech Specs

• Native MST for extended desktop and multi-display installations

• Up to 8.1 Gbit/s per lane

─ Dual lane allocation supports UltraHD resolutions

• Supports RGB And YPrPb Color Spaces

─ Up to 16 bit color

• Up to 8-channels audio

• DP++ Embedded in new USB Type C Standard

─ SlimPort provides mobile device support

DisplayPort Dual Mode supports

passive conversion to HDMI or DVI

DP++ HDMI

CH 0

CH 2

CH 1

CH 0

Sync

Green

Red

Blue

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Thunderbolt & Mini-DP

• Thunderbolt is built on the Mini DisplayPort connector and can “shift” from

TB to Mini-DP to HDMI based on configuration commands

• Thunderbolt uses data lanes for PCIe content and other “tunneling” data

transport techniques

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Thunderbolt & Mini-DP

•Thunderbolt controllers on the host

and peripherals multiplex the PCIe

and DisplayPort data into packets

and de-multiplex them at the

destination─ When connected to a DP++ compatible

device, the Thunderbolt port can provide a

native DisplayPort signal with 4 lanes of

output data at up to 5.4 Gbit/S per lane

─ When connected to a Thunderbolt device

the per-lane data rate may be as high as

10 Gbit/s and the 4 lanes are configured

as 2 channels with each bidirectional 10

Gbit/s channel comprising one lane of

input and one lane of output

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“Knowledge is a process of piling up facts; wisdom lies in their

simplification.”

− Martin H. Fischer

In Conclusion…

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What We’ve Learned…

• In the digital video domain, sampling rate bounds

resolution and bit depth (word length) bounds

saturation (intensity)

• High-bandwidth Digital Copyright Protection is an

important element of digital video

• TMDS is Transition Minimized Differential Signaling

and is the basis for DVI and HDMI technology

• DVI is inside of HDMI; the two formats are

fundamentally identical in the video domain

• DisplayPort leverages four data lanes, which it can

reassign as RGBs TMDS connections making

DP++ compatible with HDMI topology

• Thunderbolt is built on DisplayPort technology, but

uses “tunneling” to include PCIe data into the

communication lanes

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Questions?