CMOS to TTL

Thread Starter

saiello

Joined Jul 1, 2007
24
Hi All,
I have a TLC2543 ADC whose data output is CMOS and I would like to convert this to drive the TTL input pin on the parallel port. The datasheet of the TLC2543 implies that it is able to drive a TTL input but after sending the signal down a parallel port cable the data gets corrupted. I can probably use a buffer to do this but seems like a sledgehammer just for the one job. I've tried a FET transistor and this solves the problem but the data is inverted. I can correct this in software but would rather have a hardware solution. Given the many transistor types out there, is technically possible to use a simple single transistor arrangement that doesn't invert?

Thanks.
 

beenthere

Joined Apr 20, 2004
15,808
Single transistors won't do it. You would have an easier time of it using a buffer IC, like the CMOS 4049 or 4050 (one inverts, and the other doesn't). That will let you drive the cable.
 

Papabravo

Joined Feb 24, 2006
12,302
For a BJT
A Common Emitter stage will invert
A Common Collector(Emitter Follower) stage will not

For a MOSFET
A Common Source stage will invert
A Common Drain(Source Follower) stage will not

Your problem is really not CMOS to TTL, but CMOS to line driver. No logic chip was ever designed to drive more then about 12". What you need to drive a cable of any appreciable length is an IC designed for exactly that purpose. If you want to get really snarky you can go single-ended to differential on one end and differential back to single-ended on the other end.

Start by checking out the 26LS31 and 26LS32 datasheets. Those parts may be getting a bit long in the tooth, but they've always worked really well for me in many difficult situations.
 
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