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Hi,

TI's operational amplifier offerings is vast and certainly much of that has to do with the pursuit of the "ideal op-amp." Since no one operational amplifier can achieve this, the thousands of amplifiers available are designed to realize some aspect(s) of the ideal op-amp required by particular applications.

TI's operational amplifier catalog consists of TI-unique bipolar, JFET/bipolar and CMOS products that often have product prefixes such as TL, TLC, TLE, TLV and THS. Then, there are the TI second-sourced products that begin with LM, NE and others. TI acquired Burr-Brown in 2000 and that is where the OPA operational amplifier prefixes originated. Then, very recently, TI acquired National Semiconductor where the LM, LMC, LMV and other National prefixes originated. Thus, when you review a listing of TI operational amplifiers they are listed together which might seem confusing. Note, however, that they are grouped by the particular characteristic that is closest to ideal; low power, low voltage offset, very low noise, very low input bias current, wide bandwidth, etc. That is where order among the amplifiers comes about.

My suggestion is you define what electrical characteristic are most important in your application. Then use the TI operational amplifier parameter search tool to help you narrow down the products that best match your needs. Here is a link:

http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?family=analog&familyId=78&uiTemplateId=NODE_STRY_PGE_T

There are parameter check boxes that you can select and by doing so the parameters that are important in your application can be emphasized. That will reduce the list to products to those most suitable in meeting your needs.

If you find an operational amplifier that you think is correct for your application and you still have questions, then just post an inquiry to the E2E forum and we should be able to assist you.

Regards, Thomas

PA - Linear Applications Engineering

Hi,

I selected INA217 for the microphone signal amplification as it offers low noise.

I need to know if there is any document explaining its operation when input pin 2 and 3 contains an audio signal from knowles NR 3158 microphone +ve and -ve terminals and third terminal of microphone is at ground. I am using this IC without phantom power and opa137.

I am getting even low voltage signal than the input and lot of ac signal.... can some one point out what has been wrong in using INA217?

Saima

Saima,

I can only find limited information on the Knowles NR 3158. It appears that it has some type of internal active circuitry with at three-wire connection. I suspect that connections are V+, output and ground. V+ can range from 1.5V to 10V.

I do not believe that the INA217 provides any meaningful performance advantage with this microphone. The INA217 is best used with very low source impedance. The 4400 ohm impedance of the microphone is too high to derive any noise advantage. I believe that a better choice would be an op amp such as the OPA209 used as a non-inverting amplifier.

I suggest that you contact Knowles for more information on the proper connections to the microphone.

Regards, Bruce.

Hi,

Thank you for your input. I will enquire the proper mehtod for signal acquistion from NR-3158.

I will surely look OPA209.

regards

Saima

Hi,

I have used LF347N with inverting configuration, as the IC is readily available so used it to see the effects from knowles microphone. It is giving something as compared to INA217. So i will be testing more about it. Any one who can suggest better IC than LF 347N?

I know OPA209 suggested by Bruce. One problem using it  is , it doesn't have DIP package? any suggestions how to use this IC on breadboard? as i am not not an experienced user with different packages of IC.

Thanx

Saima

Saima,

The OPA134 is a good FET input audio op amp available in DIP.

Note that we are still unsure what type of circuitry may be included internal to the Knowles microphone capsule. The circuitry may be the limiting factor in performance of the circuit.

Regards, Bruce.