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THS7372: Question of THS7372 CVBS Input

Wayne Chen (Audio AE)
Genius 15950 points
Part Number: THS7372
Other Parts Discussed in Thread: THS7327

Hi Sirs,

The THS7372 datasheet specified 37.4ohm termination at CBVS input on page 1 and page 36, while it specifies 75 ohm in the EVM schematic on page 40. Would you please advise which value is better for CVBS and why?   




 
Thank you and Best regards,

Wayne Chen
07/25/2017

  • 0
    TI__Genius 15975 points

    Hi Wayne,

    The answer to your question depends upon whether it is a current or a voltage source.

    If it is a current source like the DAC which is shown in the first image you posted - Fig 89, you probably need the 37.4 ohm resistor termination to GND. For a current-source, you always look at the Norton equivalent of the input with the source impedance (75-ohms) in parallel to the load impedance (75-ohms). 

    On the contrary, the video test equipment is mainly a 75-ohm input voltage source which is why we have the 75-ohm termination to GND on the THS7327 EVM.

    Best Regards,

    Rohit

  • 0 in reply to Rohit Bhat
    TI__Genius 15950 points

    Hello Rohit,

    Thank you for your elaboration. May I say that we need 75ohm input termination if we use an external CVBS source or voltage mode DAC, and 37.5ohm termination if we use a current mode DAC?

    Thank you and Best regards,

    Wayne Chen
    07/27/2017 

  • 0 in reply to Wayne Chen (Audio AE)
    TI__Genius 15975 points
    Hi Wayne,

    Yes, that would be a correct interpretation.

    Best Regards,
    Rohit