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instrumentational amp question

We are using an INA128 instrumentation amp from TI (data sheet here:

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).

We have a signal from a function generator, that is filtered (high pass then low pass), to get it between 20kHz and 40kHz. Now we want to amplify the filtered signal in order to get a better reading on the oscilloscope. So our filtered signal is just ONE output wire, and so we are confused about where it should go into the INA128.

We are assuming that the V- and V+ (pins 4 and 7) are the pins for the voltage that we are applying to the whole system (about +/- 10V); and that the Ref (pin5) is grounded.

-Is this correct?

and

-What goes into the Vin- and Vin+ (pins 2 and 3)? `Do we put the output from the filter into one and ground the other?

Thanks for any help!

Reply to
Rhea2002
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OK why are you using a ina128, since you dont seem to have a differential signal input in the first place. What are you signal levels?

martin

Reply to
martin griffith

Hi Rhea,

What you need is a normal OP-Amp. But sure, you can use a INA, too.

That depends on your output range you want to have. The datasheet recommends

+/- 2.25 to +/- 18 V). Why using more than needed? Most scopes can operate to a few mV range. Soif your signal is too small to show this signal, may be you should focus on a very low noise design.

Yes.

Yes. But as I wrote above: You may have an other problem and may be you wouldn't be glad with your solution.

Marte

Reply to
Marte Schwarz

we need the +/- 10V because we are running it thru the filter.. and the filter chips need that much (right now) to get a good output. So we chose a voltage that agrees with both chips. the filter chip is a OPA4227.

Thanks for the other info!

Reply to
Rhea2002

Instrumentation opamps are usually used to amplifly ultra-low power signals. If you are trying to amplify the output of an active filter you could just use an opamp.

However, if your signal source is a really low power signal, then you might want to amplify it with an instrument opamp before sending it to the filter.

Reply to
Jeepster

Another google-groupie... This answer is not adressing the unique characteristics of an IA. This type of amplifier consists of several(mostly3) opamps connected in a two-stage arrangement, with two differential inputs; and the gain can be varied with a single resistor. The output is single ended. Usually the gain can be also set to a fixed value with internal resistors. It doesn't need to be high, most IA allow gains from 1 or 2 upwards. The IA is used for differential signals i.e. a dynamic mike in professional audio or in a bridge configuration for sensor conditioning.

--
ciao Ban
Apricale, Italy
Reply to
Ban

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