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Altera_Forum's avatar
Altera_Forum
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15 years ago

Triple Rate SDI question

I have question on Tripler rate SDI reference clock frequency. So far I am only using the 148.5MHZ , and it seems to work for all formats SD/HD/3G.

It is generated from an external 27MHZ oscillator via the PLL.

On the SDI userguide, there is also a 148.35MHZ reference clock listed for triple rate SDI , and it does not really explain the reason behind it.

Could somebody please tell me why/when such frequecy clock needed?

Thanks in advance,

JIMMY

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    15 years ago

    Hello Jimmy,

    I do not know if you are talking about SDI input (receiver) or SDI output (transmitter)?

    In the receiver the reference clock (rx_serial_refclk) is only need for training the receiver PLL it does not need to be frequency locked to the input data.

    So you can use either 148.5MHz or 148.35MHz.

    In the transmitter the reference clock (tx_serial_refclk) is used to generate the serial output stream so it must be locked to the video frequency 148.5MHz for 60Hz or 148.35MHz for 59.94Hz.

    BR,

    Reuven