Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Differential analog signal transfer over long cable

Status
Not open for further replies.

ArticCynda

Advanced Member level 1
Joined
May 8, 2013
Messages
439
Helped
82
Reputation
164
Reaction score
81
Trophy points
1,308
Activity points
4,238
Hi everyone,

I need to transfer 2 relatively high speed (10 MHz) analog signals (5Vpp) over a cable as flexible as possible. Coaxial cables are too bulky and stiff, so I thought to use a SATA cable + connectors and transfer the signals differentially. I've found the MAX4447 as transmitter (single ended to differential) and MAX4444 as receiver (differential back to single ended). In this application, noise immunity of the signal is super important. Distance: ca. 30 cm.

My question is, is this the best way of doing it? Which solutions would you guys suggest? Would you use the MAX4447/MAX4444 combination, or implement your own differential transceivers with op amps? Or just use a completely different approach?

All ideas and tips welcome!
 

Differential transmission of analog signals works well with all kind of fully differential amplifiers. It's hardly possible to achieve similar common mode rejection with a discrete design. I have implemented similar applications with ADI or TI amplifiers with good results, but Maxim should work as well.
 
Thanks for sharing your thoughts, FvM. Could you share part numbers of the AD and TI parts you used for this purpose in the past, so I can compare performance please?
 

Coaxial cables are too bulky and stiff, so I thought to use a SATA cable + connectors and transfer the signals differentially.
Differential certainly works, in fact I've sent video feeds down standard CAT5 cable over distances of 50 m before. However I think SATA cable and connectors is hardly optimal when the distance is only 30cm. Have you considered RG174 co-ax or similar, it is very flexible, well shielded and only 2.8mm diameter. Loss is less than 9.5dB per 100m! and it is usable up to about 1GHz.

Brian.
 

There are various forms of micro coax down to <1mm. Check Samtec.
 

I have seen some "twisted pair ribbon" that was used in
ECL-based "superminicomputer" systems for bus harnesses.
This would at least have controlled impedance and there
was a "ground-sigP-sigN-ground-..." arrangement which
ought to help crosstalk some. The cable could be peeled
apart from 8 pairs to one easily (would not be surprising
if there were wider, today).

But I'd second the micro- (or submini-) coax, I have a
small roll around here somewhere that's about 2mm OD
and real soft. Sad thing is, I mostly cannibalize it for the
silver-tinned shield which I like for ground braid on test
jigs. Put the differential signals each through their own
and they ought to come through real clean.

Though you might find that the shielded cable alone is
adequate, and save yourself some BOM cost.
 

Fully differential amplifiers e.g. AD8132, AD8137, THS4151 and various other TI types, optionally differential receivers like AD8129, but the former amplifiers may be used for receiver function as well.

I agree that cable size isn't a strong reason to use differential signaling, high signal dynamic with existing common mode noise however is.
 

Thanks for the replies everyone.

For the prototypes I've decided to use the MAX4447 as transmitter, and MAX4444 as receiver. I'll keep you updated on how well that works (or doesn't)!
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top