Microchip make some really nice op amps and programmable gain amps. 
Singles, duals, quads.
I have had good luck with several of them.  Look for low voltage/low 
power operation with close to rail to rail outputs and inputs.
Don't even have to leave Microchip.com!


On 5/10/2010 10:14 AM, Olin Lathrop wrote:
> yamanoor sairam wrote:
>    
>> I am currently trying to use the same op amp circuit to modify such
>> that I am able to read signals from probe between -2V to +2V. I
>> wanted to level shift the signal such that I am able to read the
>> signal against a scale of 0-4V. I removed the 40K resistor
>> http://mechatronicscraze.files.wordpress.com/2010/03/orp-circuit1.jpg
>>      
> There is much wrong here.  The most serious problem is that these opamps are
> intended to run from a wider supply range, and have rather large headroom
> requirements for both input and output.  The datasheet is vague on what
> happens when you power them at only +-5V, but at +-15V they require 4V
> headroom for input signals and 3V for output.  This is not likely to get
> better with lower supply voltage.  You therefore should figure these amps
> are good for +-1V input and +-2V output in your application.
>
> As for the 40K resistor (I assume you mean R16), that together with R9 sets
> the gain of the input stage.  Removing it makes the amp function as a
> comparator around 0.
>
> It's obvious you're just guessing how this circuit works.  You can't make
> meaningful changes until you do.  First I suggest ditching the TL072 in
> favor of something with less headroom required, such that it can do useful
> things with +-5V supply.  Fortunately there are many opamps that fit that
> requirement.  Next, find a basic text on electronics that covers opamps and
> read it.  Don't do anything until you understand how your original circuit
> was supposed to work (ignoring the headroom limitations of the TL072).  Then
> read the datasheet of whatever opamp you chose carefully.  Only then are you
> ready to make modifications to this circuit.
>
>
> ********************************************************************
> Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
> (978) 742-9014.  Gold level PIC consultants since 2000.
>    

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