256-fold (or even more) increase in speed on copper wirepossible IMHO
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From: Grant Edwards on 11 Mar 2010 10:21 On 2010-03-11, RalfM <rm(a)invalid.invalid> wrote: > digital data transfer on a wired copper medium is done usually by > setting a DC voltage (for example 5V) for a defined duration to > indicate a binary 1 value, and say 0V to indicate binary 0. I think > the duration of such a signal is called "bit period". > > Here are some questions & thoughts: What are the chips doing this > switching for transmitting are called? (modulator? DAC?) UART, CAN controller, SPI controller, I2C controller, Ethernet controller, etc. > How is it done one the receiving side? (via an ADC ?) How many such > binary signals can a say 2 GHz CPU generate in real-world per second? The CPU doesn't generally do it. > Such a bitwise transfer does need only a fast switching between 2 > voltage levels. Is it possible to have a transmitter/receiver that > can use more than just 2 possible values per "bit period" Yes. They're called modems. > (for example: a 12-bit ADC or DAC can detect 2^12=4096 different > values (ie. voltages). Then why use only 2 values (0/1) in copper > wired data transfers instead of using say 256 or 512 or 1024 or 2048 > or 4096 bits etc.? That called a modem. They use a sometimes large set of phase/amplitude to encode multple bits per symbol. Using phase/amplitude instead of DC level allows the signal to be transmitted over media that won't carry DC. > (ie. make the cable a "8 bit cable" :-) or more. IMHO one could > dramatically increase the speed on wired copper medium (for example a > 256-fold increase or even more would be possible). Are there such > chips which can switch fast a voltage source say to 256 different > values? ie. fast DAC and ADCs, DSP maybe? Modems. Most of which are just specialized DSPs. > Just some crazy thoughts of mine... :-) Not crazy. Just 30 years late... -- Grant Edwards grant.b.edwards Yow! Is this sexual at intercourse yet?? Is it, gmail.com huh, is it??
From: Rob Gaddi on 11 Mar 2010 14:37 On Thu, 11 Mar 2010 20:28:44 +0100 RalfM <rm(a)invalid.invalid> wrote: > Mike Paff wrote: > > On Thu, 11 Mar 2010 02:44:52 +0100, RalfM<rm(a)invalid.invalid> > > wrote: > > > >> Such a bitwise transfer does need only a fast switching between 2 > >> voltage levels. Is it possible to have a transmitter/receiver that > >> can use more than just 2 possible values per "bit period" (for > >> example: a 12-bit ADC or DAC can detect 2^12=4096 different values > >> (ie. voltages). Then why use only 2 values (0/1) in copper wired > >> data transfers instead of using say 256 or 512 or 1024 or 2048 or > >> 4096 bits etc.? (ie. make the cable a "8 bit cable" :-) or more. > >> IMHO one could dramatically increase the speed on wired copper > >> medium (for example a 256-fold increase or even more would be > >> possible). Are there such chips which can switch fast a voltage > >> source say to 256 different values? ie. fast DAC and ADCs, DSP > >> maybe? > >> > > > > Sounds good in theory, but is likely to fall apart once reality > > sets in. > > > > Think a little bit about how noise picked up by the transmission > > line will affect the reading at the receiver. Also consider the > > case where the transmitter and receiver have different ground > > references. > > I think they can be solved easily by (a) using a twisted pair cable > per direction, much like in Ethernet, and (b) one of the wires would > be the common ground and the other obviously the DC level against the > ground wire. The only problem I see is to have a DAC and an ADC which > can switch fast enough the DC levels. > But I remember having seen in the specifications of these chips > that they can well do several Mega or even Giga samples per second, > so then it should suffice IMO. Twisted pair does not equal perfect noise cancellation. It helps, but not infinitely. Then on the far end you've got to have a differential receiver, which isn't going to have a perfect common mode rejection. All the while taking into account that all of the analog signal path has to settle to whatever level you're talking about (256 levels means better than 0.5%) in well under the bit time. Basically, you're making the common mistake of really really REALLY wanting the real world to look like your undergraduate theory. The real world is hairy, nasty, and complex. If you really want to understand how much so then look into the history of the 56kbaud modem. Realize and understand that the folks working on it were very bright and very experienced, and if there was some easier answer then they wouldn't have gone to all that trouble. -- Rob Gaddi, Highland Technology Email address is currently out of order
From: Grant Edwards on 11 Mar 2010 14:40 On 2010-03-11, RalfM <rm(a)invalid.invalid> wrote: > Grant Edwards wrote: >> On 2010-03-11, RalfM<rm(a)invalid.invalid> wrote: >> >>> digital data transfer on a wired copper medium is done usually by >>> setting a DC voltage (for example 5V) for a defined duration to >>> indicate a binary 1 value, and say 0V to indicate binary 0. I think >>> the duration of such a signal is called "bit period". > ... >>> (for example: a 12-bit ADC or DAC can detect 2^12=4096 different >>> values (ie. voltages). Then why use only 2 values (0/1) in copper >>> wired data transfers instead of using say 256 or 512 or 1024 or 2048 >>> or 4096 bits etc.? >> >> That called a modem. They use a sometimes large set of >> phase/amplitude to encode multple bits per symbol. Using >> phase/amplitude instead of DC level allows the signal to be >> transmitted over media that won't carry DC. > > Doesn't Ethernet use DC? Yes. That's why I listed "Ethernet controller" as an example of a chip that does the baseband, binary, bit-serial method that was initially described. > And Ethernet uses bit-serial transfer at the lowest physical level. 10BaseT does. Some of the higher speed versions encode multiple bits per symbol. > What I mean is to replace the bit-serial part by say a byte-serial > transfer. Ie. in the same transfer cycle (time) now 8 bits could be > transferred (insted of just 1) by using more than 2 DC signalling > levels (here 8), much like how a DAC and ADC do it. Some of the higher speed Ethernet schemes sort of do that. For example, 100BaseT2 sends four bits per symbol. It uses 5 different DC voltage levels. -- Grant Edwards grant.b.edwards Yow! I want a WESSON OIL at lease!! gmail.com
From: Grant Edwards on 11 Mar 2010 14:41 On 2010-03-11, RalfM <rm(a)invalid.invalid> wrote: > WangoTango wrote: >> In article<hn9i18$m3h$1(a)speranza.aioe.org>, rm(a)invalid.invalid says... >>> >>> Just some crazy thoughts of mine... :-) >> >> http://en.wikipedia.org/wiki/Constellation_diagram > > Isn't this intended for AC signals? I was meaning DC signals like in > Ethernet. Though Ethernet is baseband, it's not really DC. Various encoding schemes are used to make sure there is little or no DC voltage. -- Grant Edwards grant.b.edwards Yow! Jesus is my POSTMASTER at GENERAL ... gmail.com
From: Grant Edwards on 11 Mar 2010 14:49
On 2010-03-11, RalfM <rm(a)invalid.invalid> wrote: > Mike Paff wrote: >> On Thu, 11 Mar 2010 02:44:52 +0100, RalfM<rm(a)invalid.invalid> wrote: >> >>> Such a bitwise transfer does need only a fast switching between 2 voltage levels. >>> Is it possible to have a transmitter/receiver that can use more than >>> just 2 possible values per "bit period" (for example: a 12-bit ADC or DAC >>> can detect 2^12=4096 different values (ie. voltages). Then why use >>> only 2 values (0/1) in copper wired data transfers instead of using >>> say 256 or 512 or 1024 or 2048 or 4096 bits etc.? (ie. make the cable a "8 bit cable" :-) or more. >>> IMHO one could dramatically increase the speed on wired copper medium >>> (for example a 256-fold increase or even more would be possible). >>> Are there such chips which can switch fast a voltage source say to 256 >>> different values? ie. fast DAC and ADCs, DSP maybe? >>> >> >> Sounds good in theory, but is likely to fall apart once reality >> sets in. >> >> Think a little bit about how noise picked up by the transmission >> line will affect the reading at the receiver. Also consider the >> case where the transmitter and receiver have different ground >> references. > > I think they can be solved easily [...] Go ahead. I'm sure all those engineers at TI, Bell Labs, DEC, Intel, HP, etc. were all wrong. You're going to have a lot of problems with waveforms changing too much. Have you ever looked at any eye-plots and and compared what comes out of the far end of a cable with what goes in? > by (a) using a twisted pair cable per direction, much like in > Ethernet, and (b) one of the wires would be the common ground and the > other obviously the DC level against the ground wire. The only > problem I see is to have a DAC and an ADC which can switch fast > enough the DC levels. But I remember having seen in the > specifications of these chips that they can well do several Mega or > even Giga samples per second, so then it should suffice IMO. Do you think that everybody goes to such measures to avoid DC signalling just for fun? -- Grant Edwards grant.b.edwards Yow! I'm having a at tax-deductible experience! gmail.com I need an energy crunch!! |