FreeLists / si-list / [SI-LIST] Re: NRZ signaling

[Mike Brown <bmgman@xxxxxxxxxx>]

Sunil,
It is also the case that NRZ can have significant low-frequency 
components - DC for a run of 1's or zeros.  In optical (and other 
serial) communications, the basic data stream is encoded to limit the 
run length of the encoded stream and to balance the number of 1's and 
0's, eliminating the low-frequency parts of the spectrum.  This permits 
the use of AC coupled components, eliminating the concern of common mode 
voltage between driver and receiver.  The encoding adds some overhead - 
25% in the case of 8b-10b encoding, but it buys some significant system 
advantages.

Regards,
Mike

herbert_lage@xxxxxxxxxxx wrote:

>Hi Sunil,
>
>The main feature of a Non-Return-to-Zero (NRZ) pattern is shown in the little 
>graph below. For consecutive "Ones" the signal stays at the logic "high" level.
>
>  
>Bit-Sequence:  0  | 1  | 1  | 0 
>       
>                   --   --      
>Return-toZero:    /  \ /  \     
>             -----    -    ------
>
>
>                  --------      
>NRZ:             /        \     
>            -----          ------
>
>
>The advantage is that the fundamental frequency of NRZ signals is only half 
>the bit rate, so it requires less bandwidth for transmission. You can see that 
>easily when you compare a 1010 sequence in both formats. In optical 
>transmission people typically use a low-pass filter that cuts off at about 
>0.8*bitrate. So for 10Gb/s data transmission you only need 8Ghz analog 
>bandwidth. 
>
>It also has a consequence when simulating NRZ patterns - if a clock-like 
>source is used, it needs to be run at half the bitrate to create a 1010 NRZ 
>signal.
>
>Best Regards,
>
>       Herbert.
>
>
>-----Original Message-----
>From: sunil-chandra.kasanyal@xxxxxx
>[mailto:sunil-chandra.kasanyal@xxxxxx]
>Sent: 04 March 2003 13:10
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] NRZ signaling
>
>
>
>
>Dear All,
>          What is the NRZ (Non Return to Zero) Signaling. How it makes high
>speed interfacing possible.
>
>Thanks and Regards,
>Sunil C Kasanyal
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