AD8134 Help Required

Hello everyone,

 

I require to convert RGsB (Gs means "Sync on Green") signals of a Single Ended video stream into Differential output.

I researched and found AD8134 to be suitable for the job. I developed an evaluation board on the resources available on Analog Site, and I looked at following discussion to create a board for AD8134 (I used the designs for AD8142 (same as AD8134) in the answer of AnnaFeB ):

 

https://ez.analog.com/message/211413#211413

 

 

However, in my card i kept the option to give a "negative 5" volt supply. In my case, i have no use for Vsync, Hsync and Sync Level pins (atleast that is what i think, since my Sync signal is on GREEN line), so there fore i have left these three signals "DISCONNECTED"

 

My issue is that once i start the board, power it up at "Positive and Negative 5 volts", and give no input, i get strange results on my outputs. the Red outputs, show no value, the green outputs show "negative 1 volt", while the blue output shows "Positive one volt". When i give an Input signal of "+1 volt" at all 3 positive inputs ( the negative inputs are grounded), i receive following outputs:

 

    1) R+ and R- show nothing

    2) G+= -1, G- = -2

    3) B+= +2, B-= +1

 

I do not think this working correctly, does this have something to do with the three signals i left unconnected?  please help..

  • 0
    •  Analog Employees 
    on Aug 11, 2015 5:16 PM

    This appears to be a duplicate of this thread: View the full discussion

    Locking this thread, look for responses in the first one.

     

    Wasn't a duplicate.. just something strange in our notifications.

    Ill ask the expert on this part to come comment.

    Dave

  • Hi, Arsalan.

    Please do the following:

    1. Connect a 17.3 or 38.3 ohm resistor between ground and inverting pin (negative input) of AD8134. Each of the negative input of R,G and B should have this for termination purposes.

    2. If item 1 does not help, follow the level-shifting of sync pulses on page 17 of the AD8134 datasheet.

    Let me know if this works.

    Regards,

    Anna

  • 1. I already had a 38.3 ohm resistor connected.

    2. And yes, the answer was in the HSYNC and VSYNC, and SYNC lines. I had left them open, but the datasheet says that they are referenced to the "VS -" pin, and since i was using a "-5 volts" VS-, i had to connected those three lines to -5. Thanks alot, all issues are fixed now!!

  • I require some more help regarding AD8134. I wish for the output differential signals to be of much higher voltage (atleast 2-2.5 V). Can you please tell me

    1) if  I should start a new discussion for this?

    2) How can I achieve this using AD8134 itself (any possible work around to this)

    A potential solution could be to amplify the input signals before feeding them into AD8134. If so, which IC would be most suitable?