Impedance mismatch or ...??

Nov 02, 2006 1 Replies
M

Hello When i connect the output of my circuit i.e. two Opamps feeding differentials signals through a step up isolation transformer and onto a twisted pair 75 Ohm impedance Bus. Then in loaded condition Signal is attenuated to about 40% of original and distorted somewhat as compared to unloaded condition. Signal is basically a bipolar +5V to -5V square wave with a Rise/Fall time of about 150ns. Is it due to Impedance mismatch or something else. Tranformer has an impedance of 4KO for



75KHz to 1MHz range of freq. Whats the solution to get rid of this problem. Thanks.
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A

Whoa! You said a mouthful.

First off, why are you using op-amps to handle a digital signal? That doesnt make much sense.

Then you say you're using a step-up transformer. That doesnt make sense either. Most op amps have output voltage and current ratios much more suited for step-down transformer setup.

Then you say the transformer has 4K impedance. That's not the whole story though, as transformers have an impedance ratio, not a fixed impedance.

You may want to consider a complete redo. There are very nice differential line driver IC's that do exactly what you need. See any major IC maker web site.

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