Inverting opamp input resistors calculation (pic) - diyAudio
 Inverting opamp input resistors calculation (pic)
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 17th July 2007, 09:17 PM #1 diyAudio Member     Join Date: Oct 2004 Inverting opamp input resistors calculation (pic) 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) or 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: http://pdf1.alldatasheet.com/datashe.../CLC200AI.html =RR=
 18th July 2007, 04:11 AM #2 diyAudio Member   Join Date: Dec 2006 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.
 18th July 2007, 09:38 AM #3 diyAudio Member     Join Date: Nov 2004 Location: close to Basel Hi, 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. jauu Calvin
 18th July 2007, 10:12 AM #4 diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders Hi, 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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