R
Rob Gaddi
Guest
Got a project where I have to interface to a third party board via two
wide 0.025" pitch ribbon cables. One of the cables goes G S S G S S
G..., and the other is even more sparsely grounded (and seemingly at
random. Thanks guys, great design job).
I'm going to be sending digital data at around 1 Mbit/s per digital line
down probably about a foot of this stuff and would love for my edges not
to ring. Hence I'd like either ballpark controlled impedance on the PCB
or a slew rate limiting driver feeding the cable.
Option A) So the specs I'm getting on the half pitch ribbon is 90 ohms
SE, 130 ohms differential. But I can't remember what assumptions go
into those numbers, and Google is being less than helpful. All of my
signals are single ended, but IIRC that 90 ohms is assuming a pleasant S
G S G pattern on the cable. Any idea what my impedance might be?
Option B) I've got something on the order of 80 signal lines to deal
with, into about 25 pF from the cable, reciever, and assorted strays.
Anyone have a recommendation on a good wide (16 bits or better) buffer
chip that can drive that with a rise/fall time of about 8 ns? I've got
3.3V and 5V available.
I'd prefer option A to B since I'm not sure how happy the driven chips
will be about those slow edges, but I'm not sure that A actually works.
Likewise if anyone's got an option C (dual Schottky rail clamps
maybe?) I'm open to it. Thoughts?
wide 0.025" pitch ribbon cables. One of the cables goes G S S G S S
G..., and the other is even more sparsely grounded (and seemingly at
random. Thanks guys, great design job).
I'm going to be sending digital data at around 1 Mbit/s per digital line
down probably about a foot of this stuff and would love for my edges not
to ring. Hence I'd like either ballpark controlled impedance on the PCB
or a slew rate limiting driver feeding the cable.
Option A) So the specs I'm getting on the half pitch ribbon is 90 ohms
SE, 130 ohms differential. But I can't remember what assumptions go
into those numbers, and Google is being less than helpful. All of my
signals are single ended, but IIRC that 90 ohms is assuming a pleasant S
G S G pattern on the cable. Any idea what my impedance might be?
Option B) I've got something on the order of 80 signal lines to deal
with, into about 25 pF from the cable, reciever, and assorted strays.
Anyone have a recommendation on a good wide (16 bits or better) buffer
chip that can drive that with a rise/fall time of about 8 ns? I've got
3.3V and 5V available.
I'd prefer option A to B since I'm not sure how happy the driven chips
will be about those slow edges, but I'm not sure that A actually works.
Likewise if anyone's got an option C (dual Schottky rail clamps
maybe?) I'm open to it. Thoughts?