Seeking the solutions of high speed interconnection for the long distance transmission of 3.3v/24MHz signals.

Hi XY, Use a length of ribbon cable. Make every other conductor ground. Use source termination on your signals to match the cable impedance in the gnd-sig-gnd mode. Make sure you connect all the grounds properly at both ends of the cable. It works well for IDE ATA parallel disks up to 133MBytes/second. HTH, Syms. p.s. BTW., ribbon cable makes great speaker wire. It's flat and fits under the carpet!

Great idea about the speaker wire! I'll have to try that next time

-Eli [Someone who hasn't been into that low cost wire adds 'distortion']

SERDES chips aren't very expensive. And the (12-bit) Fairchild Semi FIN12AC are very cheap - under $2 each and your tutor can probably get a couple of free samples.

Un bel giorno X.Y. digitò:

There are single chip with many channels, for example:

I don't think so:

Thanks for your reply. Thank you! To Symon and Peter Alfke, using ribbon cable is really a good ideal. It's simple and cheap. However, our CMOS image sensor (OV9655) is from OmniVision and is originally used on a mobile phone. It is very small not only on volume but also on power (90mW). Are you sure the attenuation is not a problem? And besides, I knew a little about the method of source terminators from the book "High Speed Digital Design" of Johnson & Graham. However, I do not understand the means of "Make every other conductor ground" and "in the gnd-sig-gnd mode" as Symon suggested. Sorry for my ignorance, could you tell me more about it?

To Tim and dalai lamah, thank you and I will try these chips later.

=3D

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OK, I understand your means. Thank you very much! I will try it!

Thank you!

Dear XY, No worries. Here are some links to show Peter and I are not making this up! Shows loss vs. length:-

Shows impedance:-

Let us know how you get on!

Cheers, Syms

(snip)

In case of low frequencies and high source impedance the cable can be treated as lumped capacitance. This was always true for magnetic phonograph cartridges, designed for 47K load using 50 ohm coax cable.

It is also true for analog telephones with 600 ohm source/load impedance and 100 ohm twisted pair cable. For telephone lines the capacitance would cause a decrease at higher (4kHz) audio frequencies. To correct for that in long runs series inductors (called loading coils) are placed in the line at regular intervals. The result is better response out to 4kHz, but it drops like a rock after that. They have to be removed for DSL to work.

It was also true for the metalization layers of integrated circuits above about 0.8 micron feature size. Converting the tools to use a distributed capacitance model slowed down the conversion to 0.8 micron and below circuitry.

The above only work where the wavelength is much longer than the cable length.

-- glen

(snip)

This reminds me on an undergrad physics lab on transmission lines. We had a pulse generator, series resistor and scope on one end, a variable resistor on the other end. Adjust the far end resistor to match the impedance, minimum reflected signal. The delay could be measured on the scope. If I remember it right the attenuation is measured with a variable capacitor on the far end, to measure the real and imaginary parts of the impedance. (I kept my lab books for some years, but don't have them anymore.) One cable we had, designed for delay, had a high inductance center conductor. The lengths were given so we could compute velocity and attenuation per unit length.

-- glen

Where a line is significantly longer than some fraction [1] of a transition time (the shortest of rise or fall time) it should be treated as a transmission line. For the newest parts, that's less than an inch.

The above works on long lines simply because the signal is in a transition state at one point on the line and *not* in a transition state much further back; put colloquially, the transition does not 'see' both points simultaneously.

Cheers

PeteS

(snip)

Well, there are two conditions for a line to look like a capacitor. One is that it has to be relatively short, and the other is that it has to be driven by a higher impedance source and have a higher impedance load. That is common in analog audio, and will be for some time to come.

(snip)

-- glen