Hello
I have the circuit shown i this white board picture
As you see, my single rail power supply is 9V and i get a 1V output for a sinusoidal 10mV input, at gain of 100,as expected.( the gain resistor is not 1k as is shown in drawing, but 530 ohm)
Notice the input signal has no Vcm (common mode) component. I just connect directly my blue 10mV sinusoidal input (from signal generator,no DC level) through two 470ohm resistors.
If i check the expected output for this scheme with AD diamond plot tool i get this:
So you see a perfectly centered signal inside operational limits.
But to do so, notice i had to set a common mode Vcm=4.5V...which is not what i had in first picture in my real board. In fact, as i understand I have Vcm=0V there!!
So, why is my circuit "working"?. If i put Vcm=0 in the diamond plot tool, i get error messages, with part of signal excursion out of good operational limits.
Also, why i get an output signal centered on 2.75V instead of 4.45 which is the VRef I used? How could i measure my real Vcm? As far as i know, ad620 needs 1.6V of common mode to work properly. 4.45 - 2.75 = 1.7V...ummm...close enought, but i don't know if this is just a coincidence or how to play with this.
Thank you.
I have the circuit shown i this white board picture
As you see, my single rail power supply is 9V and i get a 1V output for a sinusoidal 10mV input, at gain of 100,as expected.( the gain resistor is not 1k as is shown in drawing, but 530 ohm)
Notice the input signal has no Vcm (common mode) component. I just connect directly my blue 10mV sinusoidal input (from signal generator,no DC level) through two 470ohm resistors.
If i check the expected output for this scheme with AD diamond plot tool i get this:
So you see a perfectly centered signal inside operational limits.
But to do so, notice i had to set a common mode Vcm=4.5V...which is not what i had in first picture in my real board. In fact, as i understand I have Vcm=0V there!!
So, why is my circuit "working"?. If i put Vcm=0 in the diamond plot tool, i get error messages, with part of signal excursion out of good operational limits.
Also, why i get an output signal centered on 2.75V instead of 4.45 which is the VRef I used? How could i measure my real Vcm? As far as i know, ad620 needs 1.6V of common mode to work properly. 4.45 - 2.75 = 1.7V...ummm...close enought, but i don't know if this is just a coincidence or how to play with this.
Thank you.
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