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Old 9th January 2012, 12:42 AM   #1
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luvdunhill's Avatar
Join Date: Jul 2006
Default SE-BAL Conversion for Function Generators

So, I have a Tek CFG280:

Function Generators | Tektronix

I really would like to take the output and convert it to differential. I am looking at using a THAT1646 (or DRV134). Here's what I'm thinking, basically a small box with a 50 ohm BNC input connector and a three pin XLR output.

A few questions:

Does it make sense to add a input capacitor? There are many cases where I like to add a DC offset to my signal. However, does it make sense to do this into this circuit? I'm assuming this might be bad for the converter chip, and if so should I add the cap?

Does it make sense to add an input resistor to ground? Perhaps 100K or 1M? The output impedance of the signal generator is 50 ohm. The input impedance of the chip is 4K or 10K, depending on the vendor.

The datasheet discusses a scheme for common-mode offset reduction, via a pair of 10uF caps. Should I include these?

Anything else I should consider for this specific application (Tek CFG280 specifically and this use) ?
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Old 9th January 2012, 03:23 AM   #2
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Join Date: Aug 2011
Location: Utah
I'm going to go with a party line here and advise to stick to the paramaters of the data sheet. Ground pin should be ground, no resistor. That is also reference point for input low. I'd add a cap, especially if thie circuit will be outside the Tek gen. As to adding offset, HOW BIG? Data sheet says amp will swing up to 18V. At unity gain any offset plus peak signal should stay inside that window. Offset would be added at + input after blocking cap. Use a non-pole if offset will swing both ways. I'd add any caps the data sheet recomends.
Be aware that variable pulse width and duty cycles will affect respective offset anyway.

Noli timere problematum affigit
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