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:




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:


simulate this circuit – Schematic created using CircuitLab

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


simulate this circuit


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.

  • \$\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

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.

  • \$\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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