LMK04031: Audio Need to generate 1x 2x 4x of 45.1584MHz & 49.152MHz Very low jitter.

Hello Josel,

Why did you pick LMK04831? When I ran the Clock Design Architect based on your requests, it did not suggest the LMK04831 as a solution. Apart from programming one output to different frequencies and having ~100 to 200 fs of jitter, are there any other features that you need? Do you have a set input frequency? Any specific output and input types (i.e LVPECL, LVCMOS, LVDS)? Also, do you require 2 different outputs, outputting the different family of frequencies, or two separate devices?

Note that our LMHxxxx devices are made for audio applications, but it seems that the jitter from those devices won't fit your requirements. Here in blue you can take a look at them in case they do meet them and the customer is not as stringent on jitter.

Thanks,

Andrea

Hi Andrea,

Good day.

Thank you for your very good questions!
On Input, I need 2 clocks 45.1584MHz & 49.152MHz.
On Outputs, I need more than 1 yes
1]One that goes to the reclock (COAX/Optical/I2S), using a differential clock I can find a very low jitter flip flop.
2]One that goes back to the CPU (actually an XMOS) to get the bits generated at the right time (not differential)
3]I may need more than 1 for point 1 above as I have not yet found a solution to reclock I2S staying very low in jitter.

On Outputs, better to have differential output as mentioned above because low jitter flip flops use differential which makes sense.

For inputs, can I have only one clock and generate all multiples 1x/2x/4x for both base clock frequencies with the right precision? I was thinking having the 2 clocks dedicated would be better, I can find clocks at above 50fs if needed (crystech and accusilicon).

Hope I answered your questions and better explained my need.

Thank you very much!

Regards,

Josel

Hello Josel,

One last clarification question, when you say:

Joselito Go said:

For inputs, can I have only one clock and generate all multiples 1x/2x/4x for both base clock frequencies with the right precision? I was thinking having the 2 clocks dedicated would be better, I can find clocks at above 50fs if needed (crystech and accusilicon).

Are you looking to have one input or two inputs and you switch between them? From what you said above I believe you contradicted yourself.

If possible, could you also provide a visual/diagram demonstrating your need. I am still not fully understanding your description and want to make sure I design the correct solution for you. Thanks!

Best,

Andrea

Hi Andrea,

LMK5B12204 might be better adapted? Does TI have a low jitter multiplexer (2:1)?

Regards,

Josel

Hi Andrea,

Because audio requires quite precise frequencies, I was thinking to use 2 input clocks with frequencies of 45.1584MHz & 49.152MHz (which can be doubled if needed), you can check here www.audiophonics.fr/.../composants-electronique-horloges-c-600.html to better understand.

Then I need, from the control bus (I2C preferred BTW), to programmatically select between the 2 inputs and the multiplier 1/2/4x depending on the type of audio file being read.

But if you think, because of the TI chip capabilities, I can only use one input at the frequencies TBD and generates the above frequencies and their 1/2/4x multiples, I am open to any suggestions.

Hope this is clearer, thanks for your support!

Regards,

Josel

Hello Josel,

I'll get back to you by the end of the week

Best,

Andrea

Hi Andrea,

Good day,

Actually, I may just only need the 2:1 multiplexer. What could you recommend as a very low-jitter 2:1 multiplexer? If you have a D flip flop too let me know.

Regards,

Josel

Hello Josel,

Thank you for the update, I'll reply with a recommendation by tomorrow.

Best,

Andrea

Hello Josel,

From my understanding you need a device that:

Has 2 inputs that can be:

1) switched between them through I2C

2) multiplied after being inputted.

Has 2 outputs:

1) First output needs to be low jitter (around ~100-200 fs) and differential with frequency unknown as of right now

2) Second output should be single-ended with it's frequency unknown

If I have understood your use case, then note that I cannot give you an optimal recommendation with the output frequencies you are trying to use. For your user application I would recommend the LMK3806B. The LMK04821 and LMK04832 would also work and would result in lower jitter than the LMK3806B, but may be more complicated to use. The LMK5B12204 that you suggested may not work since it may not output the frequencies you desire (if you just want to output your input) and it will be more complicated to use than the other suggestions I gave. Again, I can give you better support if you tell me your output frequencies and if you can include a block diagram that would be extremely helpful. Thanks!

Best,

Andrea

Hi Andrea,

Good day.

Thank you but I need 2 inputs.
Here is the block diagram.


Please advise.

Regards,

Josel

Hi Andrea,

Good day.

I decided to go with 2 crystech clocks, a Low Jitter Clock Buffer/MUX, flip flop. And for I2S, I will use a Sample Rate converter (you have some BTW).

Regards,

Josel