Maker Pro
Maker Pro

Full duplex LVDS

A

avishay

Jan 1, 1970
0
Hello
I have to send a high speed (~600 Mbit/s), bidirectional LVDS signal on
a single twisted pair line. I wonder if it can be done by using
something that works like a telephone hybrid transformer. Is such a
design possible? Does anybody knows about example or components for
such a design?

Thanks, Avishay
 
R

Rene Tschaggelar

Jan 1, 1970
0
avishay said:
Hello
I have to send a high speed (~600 Mbit/s), bidirectional LVDS signal on
a single twisted pair line. I wonder if it can be done by using
something that works like a telephone hybrid transformer. Is such a
design possible? Does anybody knows about example or components for
such a design?

Straight from a FPGA with LVDS IO ? I don't know
whether they provide tristateable LVDS IO though.
I remember having seen multipoint LVDS drivers
with HCMOS inputs. They didn't operate at 600MBit
though, a limitation of the HCMOS. They did 400MBit
only.

Rene
 
B

Bob

Jan 1, 1970
0
avishay said:
Hello
I have to send a high speed (~600 Mbit/s), bidirectional LVDS signal on
a single twisted pair line. I wonder if it can be done by using
something that works like a telephone hybrid transformer. Is such a
design possible? Does anybody knows about example or components for
such a design?

Thanks, Avishay

If you want to do 600Mbps in *both* directions simultaneously (over one
path) then you'll have to do something along the lines of the telephone
hybrid transformer.

I've never attempted this type of rate using a hybrid (sometimes called
transhybrid) transformer technique, but it should be possible. You'll need
this type of transformer at each end of the twisted pair.

The main reason why it might be possible is because destination path
impedance is known and fairly stable. This is what allows the transformer
circuit to subtract-out each side's own transmit signal from full-duplex
path.

You could also (theoretically) use an active technique (e.g., opamps), but
getting this to work at this speed might be tricky, although easier to put
together.

Do some searching and you'll find the transformer and opamp topology. You'll
probably have to design and wind your own transformer, if you go this route.
If you use the transformer technique, it will also be necessary to encode
(and decode) your data to ensure a minimum number of edges per group of
bits. This will keep any DC component out of the signal (which can't be
passed by a transformer). 8b10b or 64b66b encoding/decoding techniques are
two examples of this.

Bob
 
M

Mac

Jan 1, 1970
0
Hello
I have to send a high speed (~600 Mbit/s), bidirectional LVDS signal on
a single twisted pair line. I wonder if it can be done by using
something that works like a telephone hybrid transformer. Is such a
design possible? Does anybody knows about example or components for
such a design?

Thanks, Avishay

It's certainly possible. Whether it can be done simply or economically or
in such a way that it qualifies for FCC or other agency approvals is
another question.

Gigabit Ethernet uses simultaneous bi-directional signaling, But not at
such a high data rate per pair. In fact, I think each pair is operating at
25 Mega-symbols per second.GigE doesn't use transformers for subtraction.
It uses either signal processing or perhaps simple analog subtraction to
remove the near-end contribution.

At your data rate I think it would be hard to go analog. But then again,
maybe not. Maybe you could use a high-speed differential amplifier to
buffer the incoming signal, then subtract a replica of the local
signal. With a truly differential amplifier, this could work, but you need
lots of bandwidth.

Best of luck!

--Mac
 
A

avishay

Jan 1, 1970
0
Thanks for everyone who has replied. From your answer I understand that
this type of solution (for this data rate) is far from being common, so
I'll probably try another approach for my problem.

Thanks again,
Avishay
 
Top