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I'm working with ICL7650S(online datasheet). I made a non-inverting amplifier but I don't know why the Gain isn't correct! this is my circuit:

figure1

figure2

figure3

The Gain should be (841k/2.14k)+1=393.99 but when I applied 6mv in the postive input I got 283mv and when applied 13mv, I got 584mv in the output. why?

Edit1: cirtuit:

schematic

simulate this circuit – Schematic created using CircuitLab

Edit2: I measured the voltage of some parts and result:

schematic

simulate this circuit

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The primary reason that you are not seeing what you expect is that you are trying to operate the part outside of its common mode range. This part is not a rail to rail op-amp. The common mode range from the data sheet is as follows:

enter image description here

When a +5V and -5V set of supplies is used.

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  • \$\begingroup\$ I just changed the supply to 12.3v for +V and 0v for -V and applied 9mv to postive input and just got 428mv! and for 115mv got 4.55v. \$\endgroup\$ – Roh May 2 '15 at 11:56
  • \$\begingroup\$ Why not try a bipolar supply such as +/-5V? This will move your reference (GND) way away from the V- rail. \$\endgroup\$ – Michael Karas May 2 '15 at 12:04
  • \$\begingroup\$ I just have positive supply and in my main circuit only should use positive supply. \$\endgroup\$ – Roh May 2 '15 at 12:51
  • \$\begingroup\$ The input range extends below the negative rail so this isn't the problem. \$\endgroup\$ – Andy aka May 2 '15 at 13:40
  • \$\begingroup\$ @MichaelKaras Please look at Edit2 in the question. \$\endgroup\$ – Roh May 2 '15 at 14:29
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I can't see how you have the following connected in your pictures: -

enter image description here

It looks you are neither using an external clocking source NOR using the internal clock. It also looks like the two capacitors on pins 1 and 2 do not connect to ground.

Your circuit shows none of this and therefore is of no use.

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  • \$\begingroup\$ As you can see in the pictures, I have connected two capacitors (two 100nf) to Cextb and CextA and they connected to Cretn. Why and how should I use the clock? \$\endgroup\$ – Roh May 2 '15 at 10:38
  • \$\begingroup\$ @Roh - Check your protoboard carefully. In the photo it looks like the Cretn wire is off by one row of holes at the common connection of the two capacitors. \$\endgroup\$ – Michael Karas May 2 '15 at 11:04
  • \$\begingroup\$ @Roh you need to apply an external clock or use the internal clock by activating pin 14 correctly (from memory) Read the data sheet - this is the first thing you should do to understand what all the pins do. \$\endgroup\$ – Andy aka May 2 '15 at 11:12
  • \$\begingroup\$ @MichaelKaras Are you sure? look at these picture: img4.uplood.fr/free/5cpt_20150502_153725.jpg and img4.uplood.fr/free/fndm_20150502_153714.jpg and img4.uplood.fr/free/rmb8_20150502_153655.jpg \$\endgroup\$ – Roh May 2 '15 at 11:18
  • \$\begingroup\$ @Andyaka I applied Vcc to INT/EXT pin and nothing happened. I think when it is NC, it means it uses internal clock and no need to other pins. \$\endgroup\$ – Roh May 2 '15 at 11:21

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