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BER measurement (Read 4827 times)
raja.cedt
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BER measurement
Aug 09th, 2013, 8:19am
 
Hello all,
Can any one please explain how BER measured in real time? For example attached is one real time bath tub curve for TIA, in that paper he gave BER from that curve directly and repeated the curve for   different inputs. I will be very happy if some one explain clearly.

THanks,
Raj.
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BER.png
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boe
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Re: BER measurement
Reply #1 - Aug 9th, 2013, 12:41pm
 
Raja.cedt,
Quote:
Can any one please explain how BER measured in real time?

Usually you stimulate your system with pseudo-random data & compare the received data with the data sent.
Does that help?
- B O E
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ywguo
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Re: BER measurement
Reply #2 - Aug 14th, 2013, 12:50am
 
Hi Raj.

Since it usually take very long time to test the BER with PRBS, BER is often estimated, calculated with jitter. If the total jitter is not less than one UI, there must me bit decision error. And the total jitter is split into deterministic jitter and random jitter. The deterministic jitter is the flat part in the bathtub curve, and the random jitter is the skirt-like part of the bathtub curve.

Since the random jitter is Gaussian distribution, then the probability of one clock edge outside the limits is calculated with erfc() function. That means the probability of bit error.

1/2×erfc(√2×α)=BER

For example, α=14 for BER=10-12. To ensure BER=10-12, Total jitter = DJ + 14×RJ must be less than one UI.

Best Regards,
Yawei
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raja.cedt
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Re: BER measurement
Reply #3 - Aug 14th, 2013, 2:43am
 
Dear ywguo,
Thanks for the reply. However i didn't understand The deterministic jitter is the flat part in the bathtub curve, and the random jitter is the skirt-like part of the bathtub curve. Could you please how?

Thanks,
Raj.
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Ken Kundert
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Re: BER measurement
Reply #4 - Aug 14th, 2013, 6:30pm
 
The deterministic jitter is large but its amplitude is bounded. Thus, the largest excursions come from the random jitter, whose amplitude is not bounded. If there were only deterministic jitters the walls of the bathtub would eventually go vertical because the amplitude of the deterministic jitter is bounded. The fact that walls have a slope to them rather than becoming purely vertical stems from the random noise (again, because its amplitude is unbounded). This is explained in http://www.designers-guide.org/Analysis/bang-bang.pdf.

-Ken
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