Re: LVDS or RS 485 for lowest EMI


"Rene Tschaggelar" <none@xxxxxxxx> wrote in message
news:42640197$0$1157$5402220f@xxxxxxxxxxxxxxxxxx
> As serial connection on desktop scale (few meter), what
> would give the lowest electromagnetic interference, LVDS
> or RS485 ? The speed is few 10kHhz to few 1 MHz.
> There are no GND issues.
>
> LVDS is 3mA into 100 Ohms while RS485 is 5V into 100
> Ohms. Since LVDS is much faster, I'd assume it to have
> less but shorter transients.
>

Typical LVDS drivers have much faster edges, which means that you will see
EMI going up to hundreds of MHz - I speak from experience. In principle use
of a twisted pair should mean cancellation of most of the EMI, but in
practise driver skew and cable asymmetry mean that the cancellation is not
perfect. If EMI is an issue, I'd go for the slowest edges I could get away
with ...

Dave




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