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Image Sensor LVDS on Flat Flex Cable?

Chris Nielsen
Intellectual 605 points
Other Parts Discussed in Thread: SN75LVDT1422

Hello.  I have an image sensor (Aptina MT9M033) that will be cabled to another pcb 2-4" away.  I'm considering using LVDS drivers/receivers over a flat flex cable using connectors or with a rigid-flex PCB construction (no connectors).

I'm new to these technologies and was wondering if anyone could share general thoughts.

A few questions:

- best to use a single layer flex cable with the differential pairs next to each other?

- best to use 2-layer flex cable with a ground plane under the diff signals?

- best to use 2-layer flex cable with the diff signals on top of each other?

- best to use 3-layer flex cable with outer ground planes and inner diff signals?

The image sensor presents an 8-bit data bus, pixel clock (48-74.25 MHz), Frame Valid signal, and Line Valid signal

Thanks, Chris

  • 0
    TI__Guru 62920 points

    Hi Chris,

    I recommend placing the differential signals close to one another and on the same layer.  You should use either a 2-layer board with a continuous ground plane underneath the differential lines, or a 3-layer board with a ground plane above and below.  This makes it easier to maintain a controlled 100-Ohm differential impedance along the length of the lines.  The ground plane also provides some shielding against noise and reduces EMI.

    To cut down on the number of conductors you need to route from board to board, you may want to look into serializing the data before it is transmitted.  For example, an SN75LVDT1422 could be used to take the 8-bit data, Frame Valid, and Line Valid signals and condense them down to just two differential pairs (plus a clock line).  At the receive end, the same part could be used to deserialize the data back into 10 parallel data signals and one clock.

    I've attached a document on High-Speed Layout Guidelines that can give you some more general info on how to go about designing a high-speed system.  Please let me know if you have any additional questions.

    Best regards,
    Max Robertson
    Analog Applications Engineer
    Texas Instruments

    High Speed Layout Guidelines.pdf
  • 0 in reply to Miguel Robertson
    Intellectual 605 points

    Good answer.  Thanks, Chris