element14 Community
element14 Community
    Register Log In
  • Site
  • Search
  • Log In Register
  • About Us
  • Community Hub
    Community Hub
    • What's New on element14
    • Feedback and Support
    • Benefits of Membership
    • Personal Blogs
    • Members Area
    • Achievement Levels
  • Learn
    Learn
    • Ask an Expert
    • eBooks
    • element14 presents
    • Learning Center
    • Tech Spotlight
    • STEM Academy
    • Webinars, Training and Events
    • Learning Groups
  • Technologies
    Technologies
    • 3D Printing
    • FPGA
    • Industrial Automation
    • Internet of Things
    • Power & Energy
    • Sensors
    • Technology Groups
  • Challenges & Projects
    Challenges & Projects
    • Design Challenges
    • element14 presents Projects
    • Project14
    • Arduino Projects
    • Raspberry Pi Projects
    • Project Groups
  • Products
    Products
    • Arduino
    • Avnet Boards Community
    • Dev Tools
    • Manufacturers
    • Multicomp Pro
    • Product Groups
    • Raspberry Pi
    • RoadTests & Reviews
  • Store
    Store
    • Visit Your Store
    • Choose another store...
      • Europe
      •  Austria (German)
      •  Belgium (Dutch, French)
      •  Bulgaria (Bulgarian)
      •  Czech Republic (Czech)
      •  Denmark (Danish)
      •  Estonia (Estonian)
      •  Finland (Finnish)
      •  France (French)
      •  Germany (German)
      •  Hungary (Hungarian)
      •  Ireland
      •  Israel
      •  Italy (Italian)
      •  Latvia (Latvian)
      •  
      •  Lithuania (Lithuanian)
      •  Netherlands (Dutch)
      •  Norway (Norwegian)
      •  Poland (Polish)
      •  Portugal (Portuguese)
      •  Romania (Romanian)
      •  Russia (Russian)
      •  Slovakia (Slovak)
      •  Slovenia (Slovenian)
      •  Spain (Spanish)
      •  Sweden (Swedish)
      •  Switzerland(German, French)
      •  Turkey (Turkish)
      •  United Kingdom
      • Asia Pacific
      •  Australia
      •  China
      •  Hong Kong
      •  India
      •  Korea (Korean)
      •  Malaysia
      •  New Zealand
      •  Philippines
      •  Singapore
      •  Taiwan
      •  Thailand (Thai)
      • Americas
      •  Brazil (Portuguese)
      •  Canada
      •  Mexico (Spanish)
      •  United States
      Can't find the country/region you're looking for? Visit our export site or find a local distributor.
  • Translate
  • Profile
  • Settings
Avnet Boards Forums
  • Products
  • Dev Tools
  • Avnet Boards Community
  • Avnet Boards Forums
  • More
  • Cancel
Avnet Boards Forums
Avnet Boards General TMDS33 to LVDS
  • Forum
  • Documents
  • Members
  • Mentions
  • Sub-Groups
  • Tags
  • More
  • Cancel
  • New
Join Avnet Boards Forums to participate - click to join for free!
Actions
  • Share
  • More
  • Cancel
Forum Thread Details
  • State Verified Answer
  • +1 person also asked this people also asked this
  • Replies 3 replies
  • Subscribers 337 subscribers
  • Views 4414 views
  • Users 0 members are here
Related

TMDS33 to LVDS

asherkim
asherkim over 7 years ago

Hi~

I would like to theoretically know how TMDS33 is converted to LVDS from the link below .  

 

http://zedboard.org/sites/default/files/documentations/AES-ZED-LCD-INT-SCH-V1_0.pdf

 

Thanks for reading. 

 

Best Regards,

Asher

  • Sign in to reply
  • Cancel

Top Replies

  • zedhed
    zedhed over 7 years ago +3 verified
    Hi Asher, It is a good inquiry since looking at the schematic, the design principle at work may not be obvious. I attached some images to this post which do not always render properly in every browser…
Parents
  • zedhed
    0 zedhed over 7 years ago

    Hi Asher,

     

    It is a good inquiry since looking at the schematic, the design principle at work may not be obvious.  I attached some images to this post which do not always render properly in every browser.  I use Firefox with this site and this seems to work fairly well.

     

    That ALI3 Pmod Interposer Board provides signal connections (LVDS & control signals) to the LCD display panels used in our display kits.

    On ZedBoard, there are two I/O Expansion PMOD Headers (JC1 & JD1) connected to PL of ZC7020 device with differential trace routing. These signals are connected to ZC7020 Bank13 with 3.3V Vcco. The High Range (HR) I/O bank does not support LVDS I/O standard with 3.3V supply (on ZedBoard this bank is fixed at 3.3V) and allowed supply voltages for LVDS are only 2.5V/1.8V. Thus, ZedBoard alone is not able to directly support the LVDS33 I/O standard required by the LCD display panel.


    To resolve the issue, the differential I/O standards TMDS which supports 3.3V Vcco in the HR bank is employed within the ZC7020 device. Thus, modification of the signaling from ZedBoard is required to convert from TMDS to LVDS33 for compatible signaling standards.

     

    The TMDS signaling standard is widely used in DVI and HDMI video interface. The conceptual schematic of one TMDS differential pair is illustrated below. Using current drive to develop the low voltage differential signal at the receiver side of the DC coupled transmission line. The link reference voltage AVcc sets the high voltage level on the differential signal, while the low voltage level is determine by the current source of the transmitter and the termination resistance at the receiver side. The termination resistance (RT) and the characteristic impedance of the trace/cable (Z0) must be matched. The normal high level voltage is AVcc and the normal low level voltage of the signal is (AVcc – Vswing). According the specification AVcc is 3.3V, RT is 50 Ohms and Vswing is between 400mV to 600mV on transmitter side.

    image

     

    The signal strength is close to LVDS signal except for the DC signal level. In TMDS, the differential signal swing below the supply voltage, but in LVDS, the differential signal swing across the reference voltage, also call common mode voltage Vcm = (Vp + Vn)/2 = 1.2V. About the signal swing magnitude on TMDS (in many cases) is also suitable for LVDS. From the above signaling mechanism, the high level is determined by AVcc, thru we can change new supply voltage on AVcc that match the LVDS signal level. i.e. 1.2V + Vswing(max)/2 ~ 1.5V.

    Please note that we adopt TMDS IO Standard on FPGA for differential output and signal level conversion. The data transmitted on those differential pairs are scrambled LVDS data mentioned in the LCD Module datasheet.

    After implementing the signal modification of ZedBoard output, a measurement on LVDS CLK signal as shown below to verify the signal level translated from the TMDS output. The measuring point is at the LVDS 100 Ohm termination resistor on the LCD module.

    image

     

    Probe Channel 1 (Yellow): CLK_P
    Probe Channel 2 (Blue): CLK_N

    The following chart shows the LCD input requirement:

     

    image

     

    From the measurement above, the DC signal peak value is 1.5V which is < 2.4V.


    The common mode voltage is 1.2V and the differential input minimum on high signal is +250mV and -170mV for low signal input, which meets the LCD display panel requirements.

     

    Best Regards,

     

    -Kevin

    • Cancel
    • Vote Up +3 Vote Down
    • Sign in to reply
    • Reject Answer
    • Cancel
  • saadtiwana_int
    0 saadtiwana_int over 1 year ago in reply to zedhed

    Hi Kevin,

    Thank you for your detailed, excellent explanation. I came across this looking for something similar.

    I have a follow-up question: I have seen CMOS/TTL-to-LVDS converter ICs, for example DS90LV011A which can do up to 400Mbps per line. Would it have been a possibility to output LVCMOS33 signals from the FPGA and put 4 of these LVDS transmitters to produce the required LVDS signals to drive the LCD? For example, 1024x768@60Hz LCDs, the LVDS signals on each line go to about 450Mhz.

    Best Regards,
    Saad

    • Cancel
    • Vote Up 0 Vote Down
    • Sign in to reply
    • Verify Answer
    • Cancel
Reply
  • saadtiwana_int
    0 saadtiwana_int over 1 year ago in reply to zedhed

    Hi Kevin,

    Thank you for your detailed, excellent explanation. I came across this looking for something similar.

    I have a follow-up question: I have seen CMOS/TTL-to-LVDS converter ICs, for example DS90LV011A which can do up to 400Mbps per line. Would it have been a possibility to output LVCMOS33 signals from the FPGA and put 4 of these LVDS transmitters to produce the required LVDS signals to drive the LCD? For example, 1024x768@60Hz LCDs, the LVDS signals on each line go to about 450Mhz.

    Best Regards,
    Saad

    • Cancel
    • Vote Up 0 Vote Down
    • Sign in to reply
    • Verify Answer
    • Cancel
Children
No Data
element14 Community

element14 is the first online community specifically for engineers. Connect with your peers and get expert answers to your questions.

  • Members
  • Learn
  • Technologies
  • Challenges & Projects
  • Products
  • Store
  • About Us
  • Feedback & Support
  • FAQs
  • Terms of Use
  • Privacy Policy
  • Legal and Copyright Notices
  • Sitemap
  • Cookies

An Avnet Company © 2025 Premier Farnell Limited. All Rights Reserved.

Premier Farnell Ltd, registered in England and Wales (no 00876412), registered office: Farnell House, Forge Lane, Leeds LS12 2NE.

ICP 备案号 10220084.

Follow element14

  • X
  • Facebook
  • linkedin
  • YouTube