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HD-SDI & CVBS signal switch

Prodigy 50 points

Replies: 8

Views: 50

Hello all,

I have one video input connector where I can have either a HD-SDI or a PAL/NTSC video source.

I'm looking for a analog switch that could route the analog signal either toward an ADV7182 in case of SDTV source or a HDTV dedoder in case of a HD-SDI source.

Routing selection will be done using an input pin of the switch.

Do you have a solution for such demand? thanks.

Regards,

Sébastien.

  • Hi Sébastien,

    Welcome to E2E. It sounds like you are looking for a high bandwidth 2:1 switch. How many channels do you need? 

    You can use the parametric search tool to filter and sort through TI's analog switches and multiplexers by configuration (such as 2:1) and parameters (such as bandwidth). 

    Depending on how many channels you need, TMUX136, TS5MP646, and TMUX1574 are good options to consider for this application.

    Best regards,
    Kate

  • In reply to Kate Dickson:

    Hi Kate,

    Thanks for your answer. this is helpful. Do you have a high bandwidth 3:1? If fact the specs may be a little bit more complicated. I do have 2 input signals (HD-SDI or a PAL/NTSC video source) and one third PAL/NTSC video source going out. All of this still on one connector.

    According the parametric search tool TI does not provide such device. I was considering using the TMUX1574 as well but I'm not sure.

    Thanks.

    Sébastien.

  • In reply to user5867317:

    Hi Sébastien,

    Could you send a block diagram of your system so I can better understand what you are looking for in a solution? I'd like to know how many channels (or bits) are needed and which signals need to be routed or selected in either direction. Then we'll see how we can configure a high bandwidth solution for you.

    Thanks and best regards,
    Kate

  • In reply to Kate Dickson:

    Please find a sketch of what I'd like to do in attachment.

    Sébastien.Schema.pdf

  • In reply to user5867317:

    Hi Sébastien,

    Thanks for providing the diagram! Sorting through all of the devices in our portfolio by bandwidth, I came up with an idea for your solution.

    TMUX1511 is a high bandwidth switch with four individually controlled signal paths (4 channel 1:1). To achieve the 3:1 mux functionality (for example), you can:

    • Tie three of the drain pins together (D1, D2, D3 as a common node)
    • Use the S1, S2, S3 pins as the signal I/Os to the FPGA.
    • Use the SEL1,2,3 control pins to select the desired path and ensure the other paths are high-Z accordingly.
    • The fourth (S4, D4) I/O pins are unused and can be terminated to ground (with a 50ohm resistor) to avoid signal reflections. SEL4 has an internal pulldown resistor to ground to ensure the unused channel is high impedance.

    As an additional note, analog switches & muxes are bidirectional and either S/D pins may be used as inputs or outputs.

    Let me know what you think about this idea and if you have any questions.

    Best regards,
    Kate

  • In reply to Kate Dickson:

    Hi Kate,

    I think this is an interesting solution. Now I'm wondering about impedance continuity and termination.

    For example, the video input of the PAL/NTSC decoder requires a 75 Ohm termination (see TVP5146M2 devices - Figure5-1 p100 of the datasheet) Analog inputs a 75 ohm pulldown resistors on each input.

    Should I have such 75 Ohm resistors before D1,D2,D3 pins and the connector. Should I also have these between the Sx pins and the PAL NTSC Decoder?

    Regards,

    Sébastien

  • In reply to user5867317:

    Hi Sébastien,

    Thanks for the follow up.

    Based on the figure of the decoder you referred to (if I'm understanding correctly), it looks like those resistors should be placed close to the video input of the PAL/NTSC (so, most likely on the Sx pin -> input of PAL/NTSC decoder).

    When the switch path is ON, it ideally acts as a low impedance "wire", so it does not seem like you need the resistors on both sides of the switch. I apologize for not providing a certain answer as this is system related, you may want to double check with the team that supports TVP5146M2 on E2E.

    Let me know if you have any additional questions!

    Best regards,
    Kate

  • In reply to Kate Dickson:

    Hi Kate,

    Thanks. you've been very helpful!

    Have a nice day.

    Sébastien.