# how to use instrumentation amplifier AD620?

Discussion in 'Analog & Mixed-Signal Design' started by ahmedzaidan, Jul 28, 2017.

1. ### ahmedzaidan Thread Starter Member

Jul 22, 2017
39
2
Hi

i need to amplify a signal from (0-5mv) using AD620 to (0-3V)?
how can i determine the gain and the reference voltage ?

Apr 5, 2008
18,510
3,570
Hello,

There is a equation for the gain:

Bertus

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3. ### ericgibbs Moderator

Jan 29, 2010
5,742
1,070
hi,
The AD620 datasheet gives all the information.
E

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4. ### ElectroHydraulicEng New Member

Mar 31, 2017
2
1
You need a gain of 600. On the datasheet gain is given by (on page 3):

G = 1+ (49.4 kohms/Rg)

Rg = 82.5 ohms

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5. ### ahmedzaidan Thread Starter Member

Jul 22, 2017
39
2
thanks a lot guys
and what is the purpose of Vref?

6. ### crutschow Expert

Mar 14, 2008
19,826
5,545
Vref is an input that determines the output voltage for 0V differential in.
Normally it is tied to circuit common.

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7. ### ahmedzaidan Thread Starter Member

Jul 22, 2017
39
2
thanks a lot ^^
i have tried RG=82.5,V+=5,V-=0,ref=0, input=1mv
output=4.57 V ?!
any thing wrong?

Apr 5, 2008
18,510
3,570
Hello,

An instrument amplifier usualy needs a dual powersupply.
V+ = +5 Volts, V- = - 5 Volts, Vref = 0 Volts.

Bertus

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9. ### crutschow Expert

Mar 14, 2008
19,826
5,545
Yup.
What are the power supply voltages?
You need a dual supply for that device.

10. ### ahmedzaidan Thread Starter Member

Jul 22, 2017
39
2
so it is impossible to use single power supply !!

is there other instrumentation amplifiers work with single power supply ?

i have tried v+=5,V-=-5 ,Vref=0.

it worked fine..

i need to use microcontroller to read the the output of ad620 .
should i need to add other elements?or connect it directly?

11. ### crutschow Expert

Mar 14, 2008
19,826
5,545
Why do you need an instrumentation amp?
Can you use a standard op amp?

12. ### ahmedzaidan Thread Starter Member

Jul 22, 2017
39
2
can i use standard op amp with load cell ?

13. ### crutschow Expert

Mar 14, 2008
19,826
5,545
Is the load cell in a bridge?

Last edited: Jul 28, 2017
14. ### ericgibbs Moderator

Jan 29, 2010
5,742
1,070
hi a,
The AD623 will work with a single supply voltage.
We need to see your circuit diagram.
E

Jul 22, 2017
39
2
16. ### ericgibbs Moderator

Jan 29, 2010
5,742
1,070
hi a,
That is a half bridge, using passive resistors to make up the other half bridge into a full bridge, it is often configured in that way.

Do you have a AD623 or any regular OPA's that you could use for the amplifier.?

E

Jul 22, 2017
39
2

18. ### ericgibbs Moderator

Jan 29, 2010
5,742
1,070
hi a,
This is a draft circuit for the AD620, uses +/-5V supply to give 0v thru 3V out.
Have used 350 Ohms for the simulation.
E

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19. ### ericgibbs Moderator

Jan 29, 2010
5,742
1,070
hi,
If you have only +V supply available, there is this option, using LM324 after the AD620.
E

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20. ### ahmedzaidan Thread Starter Member

Jul 22, 2017
39
2
Hi ericgibbs,