# Select a suitable opamp...

1. May 11, 2015

### lcr2139

1. The problem statement, all variables and given/known data
Select a suitable opamp to interface the hydrophone. Ideally the hydrophone noise will dominate the system. Consider the input referred 1. voltage noise, 2. current noise, 3. input capacitance, and 4. input impedance of the opamp.

http://www.dtic.mil/dtic/tr/fulltext/u2/a265915.pdf

2. Relevant equations
which opamp would have noise dominate the system, inverting or noninverting?

3. The attempt at a solution
inverting/non inverting opamp described in link.
i think I would pick an inverting/noninverting opamp, but which have noise dominate the system?
I read the article and I am confused at this part.

2. May 11, 2015

### Svein

3. May 12, 2015

### CWatters

I only looked at the conclusions (on page 24 in the link). It says..

"Examination of the two amplifier configurations showed nearly identical signal-to--noise ratio".

4. May 12, 2015

### CWatters

PS: The problem statement says..

"Ideally the hydrophone noise will dominate the system"

So I think your first step is to quantify the hydrophone noise. Then ensure that the noise introduced by the pre-amp is significantly lower than that.

5. May 16, 2015

### lcr2139

I now understand that I have to do research to find approximately the perfect opamp. However, I do not know how to calculate voltage noise, current noise, input capacitance, and input impedance.

6. May 16, 2015

### Svein

Look at post #2!

7. May 16, 2015

### rude man

You don't calculate these, you look them up.
Once you determine whether voltage noise, current noise, and/or other op amp parameters are of significance in your particular application you can go to a website like TI's or Analog Devices's and select the best unit.
http://www.analog.com/parametricsearch/en/10294#10294/p299=95|50000000&p4502=7000|50000000&p4101=0.0000000008|1e-8&d=sel|0|-1|299|4502|300|4101|2839|2840|4095|4108|164|-3|4118 [Broken]

Last edited by a moderator: May 7, 2017