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CDCE6214-Q1: What is Digitally Controlled Oscillator (DCO)? & How to get a better 156.25MHz differential clock?

Hailiang Zhang
Expert 7565 points
Part Number: CDCE6214-Q1
Other Parts Discussed in Thread: CDCE6214

I am helping a customer generate 156.25MHz differential clock signal with CDCE6214. I want to know what does “Digitally Controlled Oscillator (DCO)” do? Can it be used to optimize the clock signal? How to configure to get a better 156.25MHz differential clock?

  • 0
    TI__Mastermind 18070 points

    Hi Hailiang,

    If you don't need to increment/decrement output frequency then don't worry about DCO. To optimize the clock, choose the largest possible PFD (Phase Frequency Detector) frequency and start with default loop filter settings.

    Regards,
    Hao

  • 0 in reply to Hao Z
    TI__Expert 7565 points

    Hi Hao,

    For a fixed clock frequency, DCO is not needed. The frequency can be increased or decreased through DCO. And the increment/decrement is not suitable for closed-loop control of the clock frequency. Are these opinions correct?
    In addition, Could you please help me in this case? Another 25M single end clock is needed.  Why even though OUT0 is enabled, OUT0 does not work when OUT4 is disabled?

    Regards,

    Hailiang

  • 0 in reply to Hailiang Zhang
    TI__Mastermind 18070 points

    Hi Hailiang,

    The DCO is for closed loop control. It increments/decrements output frequency by adjusting the fractional feedback divider. 

    OUT0 shares the same supply rail with OUT4. So OUT4 needs to be powered up for OUT0 to show up. However, you can still set the output format of OUT4 to "disable" if OUT4 is not used.

    Regards,
    Hao

  • 0 in reply to Hao Z
    TI__Expert 7565 points

    Hi Hao

    Thank you very much!

    The customer wants to check the EEPROM value at power up. If it is correct, the CDCE6214 will work according to the value. Does this need to use Fall-Back mode?

    In addition, I am wondering if there is no need to check the value of EEPOM and I2C is not used, will the configuration in the EEPROM be used directly at power up instead of the default configuration?

    Thanks.

    Regards,

    Hailiang

  • 0 in reply to Hailiang Zhang
    TI__Mastermind 18070 points

    Hi Hailiang,

    You can follow the CRC guidelines in the datasheet if you want to perform CRC check at every power up. This makes sure that EEPROM content is not corrupted.

    However, to ensure that the EEPROM content is written correctly, it is recommended to use Direct Access method and read back all the EEPROM image bytes after writing them then compare all the bytes one by one. This only needs to done once after you write to the EEPROM. Then you can perform a quick CRC check at every power up later.

    Regards,
    Hao

  • 0 in reply to Hao Z
    TI__Expert 7565 points

    Hi Hao,

    Thanks. This is a good solution.

    In addition, I am not sure how to make the device work according to the configuration in the EEPROM at power-up. Does this require additional enablement?

    Regards,

    Hailiang

  • 0 in reply to Hailiang Zhang
    TI__Mastermind 18070 points

    Hi Hailiang,

    You can do it in the EEPROM page in Ticspro. Right hand side is register commit method. After writing EEPROM to the device, you can then read back EEPROM image (64 bytes) from the left hand side button. Once you have the EEPROM image, you can use the direct access method by clicking "write file to EEPROM" for future EEPROM writing. Detailed register level operation can be found in the datasheet.

    Regards,
    Hao

  • 0 in reply to Hao Z
    TI__Expert 7565 points

    Hi Hao，

    Thank you very much.

    Does the "a good known configuration" mentioned in P33 of the datasheet mean a configuration in EEPROM, or default configuration? 

    Regards,

    Hailiang

  • 0 in reply to Hailiang Zhang
    TI__Mastermind 18070 points

    Hi Hailiang,

    This just means that you need to avoid "pin mode" for the current configuration. As long as you can access I2C, you are done with this step.

    Regards,

    Hao

  • 0 in reply to Hao Z
    TI__Expert 7565 points

    Hi Hao,

    Could you please tell me how to directly adopt configuration in EEPROM  at power-up? I did not find it from the data sheet.

    Regards,

    Hailiang

  • 0 in reply to Hailiang Zhang
    TI__Mastermind 18070 points

    Hi Hailiang,

    Do you mean the direct access method? It can be found in the datasheet 9.5.2.3.2 

    Regards,
    Hao

  • 0 in reply to Hao Z
    TI__Expert 7565 points

    Hi Hao,

    Thanks for your kind help.

    I am wondering whether the device can work normally without IIC after writing data into EEPROM, and how to make it?

    Could you please help check the following understanding:

    After the words are written into the EEPROM through I2C, when the device was configured as interface mode, the data in the EEPROM can be written into the register through I2C, thereby adopting the configuration in the EEPROM; or when configured as the Pin Mode, the data in the EEPROM is directly adopted. When there is no I2C, the working state of the device is determined by the data written in the EEPROM before and the hardware circuit.

    Thanks and best regards,

    Hailiang

  • 0 in reply to Hailiang Zhang
    TI__Mastermind 20900 points

    Hi Hailang,

    please read datasheet section 9.3.5 Control Pins. This explains how to select one of the EEPROM pages after you have programmed them.

    regards,

    Julian