[SOLVED] instrumentation amplifier

[smu]

we are building eeg circuit for which we require instrumentation amplifier ad620 .. can any one tell about its availability in india..IF not any other way to build this amplifier..

 

[KlausST]

Hi,

sorry, can´t tell about availability in india.

******

There are many other instrumentation amplifiers. Just check if they meet your electrical specifications.

Also there is the possibility to build an instrumentation amplifer with the use of 3 OPAMPs.

Klaus

 

[ud23]

search on element14 india it must there.

 

[Audioguru]

Can't you order anything from The West? Oh, sorry, you said "we" so I guess you are young school kids without a credit card. Ask your mom, dad or teacher to order one for you.

Just now I went to www.farnell.com and clicked on the flag of India. Their location in India and many other countries is called Element 14. They have more than 2000 AD620 ICs in stock and each costs Rs.649.45. Their closest warehouse to India is in SG where-ever that is.

Or you can simply look at the datasheet of the AD620 to see what is inside: 3 opamps and 7 extremely well-matched resistors.
I have matched resistors by buying 20 or 50 of them and measuring and charting the resistance of each one then selecting pairs that measure the same. The circuit is a very simple and common differential amplifier.

 

[KlausST]

Hi,

see what is inside: 3 opamps and 7 extremely well-matched resistors.

I´m pretty sure for an eeg device you don´t need very high precision, because signal changes because of electrode to skin conduction.

But you need good match in the second stage (difference amplifier) for good CMRR. You may also adjust _one_ resistor (to the other three) for good CMRR.

Klaus

 

[Audioguru]

Even if you make a discrete instrumentation amplifier with 3 opamps and matched resistors, the datasheet for the AD620 shows how much better its common-mode rejection is. You do not want 50Hz or 60Hz of hummmmm on an EEG but you do want the low audio frequencies created by a brain.

 

[smu]

but we are finding the disturbance in circuit using op amp is very high so we are searching the suitable ic..

 

[Audioguru]

but we are finding the disturbance in circuit using op amp is very high so we are searching the suitable ic..

"The disturbance in circuit" does not have any meaning in English. You need to describe the "disturbance". Is it 50Hz mains hum? Is it part of the waveforms are rectified or clipped?

Please post the schematic of the circuit you used and show resistor values, opamp part numbers and supply voltages.

 

[hobbyckts]

If you need 1 or 2 Ic's you can get it as samples or else order but both should be through authorised distributors only. So for samples you need to provide the correct application and annual usage of the components from your side.

If you cant able to explain it clearly kindly post your schematics which will be helpful for everyone to provide the exact answers to you...

 

[smu]

hello every one.. sorry for this delayed reply..
the circuit we are working on is of link
https://people.ece.cornell.edu/land/courses/ece4760/FinalProjects/s2012/cwm55/cwm55_mj294/

we got the ic's but of 8pin ic .. and the circuit is of 16pin ic's .
can any one help us with the function of 11th pin to that of in an 8pin ic.. or any data sheet of that 16pin ic for us to solve this prob..
am attaching the image of the circuit we are working on..

 

[Surendhar Murugan]

https://www.analog.com/media/en/technical-documentation/data-sheets/AD8231.pdf

check this datasheet. details given at the first page.