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Combine power feed and data link via cable for remote peripherals

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tkc1
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re: Combine power feed and data link via cable for remote peripherals
tkc1   1/18/2012 7:43:09 PM
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Power over cable is not a new idea. My roof top has an amplifier that draws power through the coax cable. You mentioned another good example on the old voice-band POTS lines that power our phones with 48V from central office through voice band transformers. Same basic theory behind, but implementation depends on the speed and signal bandwidth. SerDes receivers have good CMRR to reject supply noise. Balance is the key for differential signaling in the same pair.

tkc1
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re: Combine power feed and data link via cable for remote peripherals
tkc1   1/18/2012 7:31:34 PM
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Putting everything into one pipe is great, but certainly challenging to engineers to make sure all these pieces running in the same pipe does like each other. And you are right, they are all analog problems.

tkc1
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re: Combine power feed and data link via cable for remote peripherals
tkc1   1/18/2012 7:27:06 PM
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Hi Sharps_eng, Yes, PoE has been around for many years, and is specified to ethernet uses to power remote devices. Ethernet uses signal transformer with bandwidth of about 100-200MHz to let the 10/100/1000Mbps ethernet signal passes through, and injects DC power at the center tap of the transformer. For SerDes with Gbps line rate, high bandwidth transformer is not cost-effective, and AC coupling is commonly used, and thus another scheme to inject power as shown in this paper. Yes. Balance is important, and common mode DC injection into the P and N signals is intended to keep the balance. regards, tsun-kit.chin@ti.com

zeeglen
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re: Combine power feed and data link via cable for remote peripherals
zeeglen   11/16/2011 5:56:28 PM
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Interesting article, but as mentioned above did not include other forms of phantom power such as used for CATV and T1. As a lab experiment I once used the center taps of the transformers on a working Ethernet Cat3 cable as tip/ring of a POTS. Ringing voltage did not affect the Ethernet function. The major concern was no guarantee of voiceband common mode rejection between the two individual pairs, so we never pursued the idea.

wfbrowniii
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re: Combine power feed and data link via cable for remote peripherals
wfbrowniii   11/16/2011 2:11:03 PM
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I used to work in the Broadcast TV radio business and designed many a everything over one coax link. DC power, on-off shift keying for a data/control channel, 70MHz if with multiplexed FM video and up to 4 audio channels and 2Gig uWave. It was far more analog than most people want to tackle now a days though.

sharps_eng
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re: Combine power feed and data link via cable for remote peripherals
sharps_eng   11/12/2011 9:50:21 PM
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Did I miss something or did this article overlook PoE? That is a system that already has all the details sorted, with low-cost parts here or on their way. I think it should have been mentioned (PoE Power-over-Ethernet). I have used this SERDES technology and it it is amazingly effective and reliable. I would certainly consider it again for reducing the bulk of shorthaul multibit connections. You have to watch the balance between the diff pairs though, or serious EM emissions will result!

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