LRC and BCK Clock setting for AD1938

Hello,

I need your help to get some additional information while using AD1938.

If AD1938 is configured in master mode, will it continuously generate LRC and BCK even if all channels of ADC & DAC are muted?

Also, can someone please help me understand the rationale on why BCK and LRC clocks are free-running? Which operating scenario will demand BCK and LRC clocks to remain free-running?

Appreciate for your help and attention on this support request.

Regards,

JP

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  • 0
    •  Analog Employees 
    on May 20, 2019 8:34 PM

    Hello JP,

    Yes, the LR clock and Bit clock will continue to run. They are simply divided down from the internal master clock rate. Just because you are muted the part internally is still being clocked and so the LRCLK and BCLK continue to have output. 

    The muting function is an audio function where the audio data goes to zero. It has nothing to do with the clocking section of the part. 

    There are many systems that operate using TDM8 with a sampling rate of 48kHz. This produces a bit clock rate of 12.288MHz which is exactly the desired frequency of the master clock in many systems. So the bit clock is used to drive the system master clock. So you would not want this to go away when the audio is muted. 

    In other systems the serial port output may go to a class-D amplifier with an I2S input. These parts often have a sleep mode that is entered when the bit clock goes away. There is a short startup time once it returns. It has to lock to the signal again. So if the bit clock never goes away you do not have that start up time when you want to un-mute. 

    If you need to stop the clocks then simply write to the register and place the serial port in slave mode and the clocks will stop. 

    Dave T

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  • 0
    •  Analog Employees 
    on May 20, 2019 8:34 PM

    Hello JP,

    Yes, the LR clock and Bit clock will continue to run. They are simply divided down from the internal master clock rate. Just because you are muted the part internally is still being clocked and so the LRCLK and BCLK continue to have output. 

    The muting function is an audio function where the audio data goes to zero. It has nothing to do with the clocking section of the part. 

    There are many systems that operate using TDM8 with a sampling rate of 48kHz. This produces a bit clock rate of 12.288MHz which is exactly the desired frequency of the master clock in many systems. So the bit clock is used to drive the system master clock. So you would not want this to go away when the audio is muted. 

    In other systems the serial port output may go to a class-D amplifier with an I2S input. These parts often have a sleep mode that is entered when the bit clock goes away. There is a short startup time once it returns. It has to lock to the signal again. So if the bit clock never goes away you do not have that start up time when you want to un-mute. 

    If you need to stop the clocks then simply write to the register and place the serial port in slave mode and the clocks will stop. 

    Dave T

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