neural ( uV ) signal amplifier

neural signal amplifier

Hello all !

I have to amplify neural signals (signals emitted by nerves) .These have the parameters :

<40 Hz ; <200 uV ; Very very low current

I need them to be amplified to above .25 V ( for low noise at ADC)

From what i know of analog design, i understand that i need :

Low input bias current or high input impedance

low offset voltage

So,

1) Am i correct ? Is there any other parameter to be considered ?
2) Any suggestions for a device ? A CMOS op-amp ? Or an instrumentation amplifier ?

The optimal amplifier selection depends also on the electrode properties, but low-noise FET OP is generally a good choice.
JFET is possibly preferable to MOSFET because of a lower 1/f noise corner frequency. FET instrumentation amplifier
is best for differential signal acquisition.

OPAX369 for ex., but better is:
very low offset & noise OP-LMP2022, you can apply it up to ca. 200Hz, but with worser Cmrr capabilities ca. up to 5KHz, and has Ibias at +/-30-200pA.
My be AD8538/8539 are better for your apps, than
AD8605,06,08 and others....
K.

Thanx a lot guys !!!

The op amps mentioned here look fantastic...but i'm a university student and it's tough for me to get them.

However,i've found that TI will send samples to me , completely free and very fast !

So i found these two:

OPA129 : Ib about 200fA !!!
OPA124 : Ib=1 pA (but half the noise)

First i was going for OPA129 but then realized that even board leakages would far exceed 200 fA .

So i guess OPA124 is better...
Please correct me if I'm wrong.

Hi prateek_k_chd,
Yes TI, LT (Linear Technologie) National Semi & most ADI (Analog Devices) & so on are usually very generous
What better is:
depends every time from some factors:-(, then you can select a butyful IC for an apps, but in your production is (for exampl.) too expensive, you can not have in a package styl...
You are right, at pAmpers is Board (&cable)LEAKAKAGE is a real PROBLEM!
Input pins are to guard(please refer to datasheets), you must see how you can put some better isolation, teflon, under solderpoint for In-pins on your PCB-IC & what kind of cable can you use!?
Cables do not do leakaging, but they are noisy too in so an application...

You must be carful with Offsetvoltage (& datasheet specifications generally:-() too!
Opa129 has it up to 2mv(at 25Cels.) but in temp-range & with your amlifying factor it can be very much.
Can you accept an outputoffset at ca.300mV?
Same over Ibias; the 100fA is tur as typical, with some parameters, but if you have for exampl. lot more powerdissipation (Load effect), then it will be rise up to ca. 30 times...
OPA124 is surly cheaper & if its paramater are enough good for your aspects-clear, thes is to select.
After montage-tests please make washing your PCB, than handsweat is the most wors stoff(+dust & rest of soldering), your enemy, for your application!!

Tnx for your points too!
K.

Alright then ! OPA124 it is !
Thanx all !