The circuit you show is for an op amp without offset adjustment pins. Think of the gain of the op amp as the slope of a linear curve of the form y=mx+b. The slope m, is the gain which is set by the ratio of feedback to input resistors. The offset is the y intercept (b) of the linear curve which is determined by the voltage at the non-inverting input. By applying a voltage to the non-inverting input the slope (gain) is unaffected but it is referenced to the y intercept (b), which is the offset voltage applied to the non-inverting pin. ----- Original Message ----- From: "yamanoor sairam" To: "Microcontroller discussion list - Public." Sent: Tuesday, May 11, 2010 3:06 AM Subject: Re: [EE] Opamp design doubt > Dear All, > > I thank you very much for the support you have extended. I must thank > Mr.Marcel Duchamp, Mr.Russell McMahon, Mr. Dwayne Reid, Mr.Mike Hagen, Mr. > Olin Lathrop for their opinion and suggestions. I was able to test the > output of the opamp for the range of -2V to +2V. When I removed the > resistor R9 and adjusted the offset voltage to 1V, I was able to infer > that the circuit spans between -2V to 2V and my output is 0-4V. > > However, I tried to understand the concept of offset voltage in an opamp > from the link below: > http://www.ecircuitcenter.com/Circuits/op_voff/op_voff2.htm > > I am not able to understand the concept entirely. Can anyone throw some > light on this? > > I must thank Mr.Marcel for having helped me through out the development. I > am still studying the stability of the ORP system. > > I must thank Mr.Russell and Mr. Olin for their opinion on the stability of > the TL07X amplifiers and I shall ensure that I check their findings > completely. > > Mr.Olin also pointed out the approach that I have taken for designing > opamp circuits. I regret that I have a very poor knowledge about opamps > and I am trying to improve myself by designing a few circuits from > scratch. > > Mr.Olin, would you mind recommending a book like this to me? > http://books.google.co.in/books?id=0zqU01lKPCEC&dq=Op+Amps+For+Everyone&printsec=frontcover&source=bn&hl=en&ei=NgDpS5T-M5O1rAez0fnzCQ&sa=X&oi=book_result&ct=result&resnum=4&ved=0CCUQ6AEwAw#v=onepage&q&f=false > > Mr. Mike, thanks for the suggestion on Microchip op amps. > > Thank you. > > Yours Sincerely, > Sairam > > > > ________________________________ > From: Marcel Duchamp > To: Microcontroller discussion list - Public. > Sent: Tue, May 11, 2010 4:52:37 AM > Subject: Re: [EE] Opamp design doubt > > On 5/10/2010 9:18 AM, Marcel Duchamp wrote: > >> You are very close to the answer. Try removing R9 - this will change >> the gain of the input amp from +2 to +1. With an offset adjust value >> around +1V, you should get what you are looking for. >> >> Why the change? You have an input voltage range of -2V to +2V ==> 4V >> span. You want an output span of +4V to 0V ==> 4V span also. Thus, you >> need a system gain of -1 which your second stage already has. > > Sairam, by now, you have seen several conflicting suggestions. I still > stand by what I wrote. I knew of the common mode range versus power > supply levels limitation but it was my impression that you were > successful with using it with the ORP application. That may have been > incorrect on my part. But if you were successful before using it then > it should work here as well. It is something for you to look into to > verify correct operation. > > The data sheet is quite clear about unity gain operation. There should > be absolutely no problem with that. Removing R9 will indeed make the > first stage function with a voltage gain of unity. > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > > > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist