26 Nov
2014
26 Nov
'14
8:03 p.m.
On Wed, Nov 26, 2014 at 8:47 PM, Billy Pettit <bpettitx at comcast.net> wrote:
ECL, if done properly, uses a terminator on every
signal line. On MECL it is usually it's 560 ohms to -5.2v or 220 ohms to -2.2 volts.
Because most circuits have two ouputs, signal and not signal, termination gives you almost
a steady load.
That most ECL circuits have differential outputs is a common
misconception. Look through a 10K or 100K databook. The vast majority
of the parts have single-ended inputs and outputs. When a single-ended
signal crosses a power supply domain, if the supplies aren't very
close, bad things can happen.
One approach to dealing with that would be to use only differential
parts, but that rules out any of the MSI parts (counters, adders, most
registers, etc.), so you end up using a lot more ICs. Another
approach is to use single-ended on a module, but only differential
between modules. To do it properly, the differential signals between
modules need to be twisted pairs.
The KL10 mostly uses single-ended signals between modules, with
differential over twisted pairs used mostly for clocks.