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Old 17th July 2007, 08:17 PM   #1
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Default Inverting opamp input resistors calculation (pic)

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This device has an internal 2k feedback resistor.
The pdf scan is poor, and I am confused about the INput resistor that goes to ground.
It looks to be either :
Rl (load)
Rf (fdbk resistor)
.....but Rf is already the internal 2k, right ?

Perhaps I don't understand the part of the equation:

"For Zin = 50 ohm, select Rg || Rf , =50 ohm" ...what does that mean ?

whole datasheet:

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Old 18th July 2007, 03:11 AM   #2
radtech is offline radtech  United States
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I'm going to say it's Ri for input.
The equation means if you want the input impedance to be 50 ohms (very common in RF work) you should select Rg and Ri (not Rf) to equal 50 ohms when connected in parallel (for instance both 100 ohms).
Rg by the way, controls the gain.
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Old 18th July 2007, 08:38 AM   #3
Calvin is offline Calvin  Germany
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the CLC200 is an old Device intended for RF use. For Audio its parameters are far from optimal.
So whats the application You are going to use it for and what gain do You need?

Radtech´is right. The resistor connecting from Vin to Gnd is Ri
The || signs mean ´parallel to´. So Zin calculates to:
Zin= Ri*Rg/(Ri+Rg) Keep in mind, that 50Ohms may be too low as load for the signal source to drive it properly, or changes the calculated values when used as buffer in filter circuits, etc etc.

Rf is the internal feedback resistor value, connected from Pin8 to Pin5.
2k is an already low value, which leads to even smaller Rg values, hence small Zin values (even with the low gains typical for Audio)!
Raising Rf´s value by using an external resistor You´d probabely have to compensate with a little cap connected to Pin4. If You have measurement possibilities You could do that, otherwise..hands off!

Summed up, I wouldn´t recommend or use the CLC200 for typical lowgain audio stages. There are lots of cheap and modern devices around that do a better job in that application area.

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Old 18th July 2007, 09:12 AM   #4
AndrewT is online now AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
had a quick scan thro' the datasheet, is this a current feedback opamp?
4000V/us is fast, but is it suitable?
regards Andrew T.
Sent from my desktop computer using a keyboard
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