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DS280DF810: PPM error count tolerance

Part Number: DS280DF810

Hi 

We have conducted some OLT4.4 rate Experiments using DS280DF810.

And following is config and sequence of initialization of CDR.

Register in hex

Value in hex

Remarks

Fc

1

 

ff

3

 

0

4

 

a

c

 

2f

70

 

31

40

 

1e

2

 

8e

0

 

3d

98

 

3f

41

 

3e

44

 

60

E1

OTL4.4 data rate;27.952 Gbps

61

C5

 

62

E1

 

63

C5

 

64

ff

 

9

4

 

18

0

 

a

0

 

 

With above settings Traffic comes up.

But PPM jump /error is there when we read from registers 0x3b, 0x3c after manually starting PPM error count with 35-> 0x2f

Values we see in for eg :3b -> 34, 32 etc., 3c->00 ; verified couple of channels. We are getting PPM error count.

What is tolerance of this or any limit for this PPM for 27.952 Gbps data rate?

And how to reduce this PPM error count, ways to reduce?

 

Thanks

Suresh

Sr, Manager, R & D, POTP HW
Tejas Networks Ltd

Bangaluru

  • Hi Suresh,

    I'm looking into the "PPM_GET_error" function in the context of your questions and will plan to provide feedback soon.

    Question: Can you confirm whether the retimer CDR is actually losing lock when you are using the PPM error function? CDR lock status can be monitored via channel register 0x78 bit 4.

    Cordially,

    Rodrigo Natal

    HSSC Applications Engineer

  • Hi Suresh,

    register 0x35[7:6] defines the criteria to declare LOCK or loss of LOCK. The register 0x35 allows the user to relax the PPM tolerance.

    In the DS280DF810 retimer, the VCO frequency is checked using the reference clock and then LOCK is declared if the VCO frequency is within 1000PPM of the indicated rate. The register 0x35[7:6] allows to increase the tolerance to higher multiples.

     

    Question: Can you confirm whether the retimer CDR is actually losing lock when you are using the PPM error function? CDR lock status can be monitored via channel register 0x78 bit 4

     

    -Rodrigo

  • HI Rodrigo

    OK..PPM tolerance is well within limits

    Thanks for clarifications

    CDRs are always locked, we get  0x78 --> 0x30 

    Regards

    Suresh