amplifier for hydrophone(use of giga ohm resistor in circuit)

siddhartha satpathi

i would like to build an amplifier for my hydrophone (reson tc4013). it is a piezoelectric sensor with sensor capacitance of 4.3nf attached a 6m long cable with capacitance 600pf. i read the application report on this link http://www.ti.com/lit/an/slyt369/slyt369.pdf and sloa033a..i guess a charge amplifier would be best for my purpose considering i have a long cable with much higher capacitance than sensor. the problem is in the circuit i need feedback resistor upto few giga ohm which is hard to procure in my case.can anybody help me with any improved circuit which uses resistors upto 5 megaohm. i wasn't able to understand why using a T network in feedback circuit would give a worse SNR as was mentioned in the application note.

over 13 years ago

0 Collin Wells over 13 years ago

TI__Guru 63885 points

Hello Satpathi,

There are many threads on the forum already regarding capacitive sensors, try searching through some of the other posts for research. Here is a very similar thread on the same app note you cite:

http://e2e.ti.com/support/amplifiers/precision_amplifiers/f/14/p/192725/691977.aspx#691977

There are also several other posts on voltage amplification for hydrophone / geophone / microphone applications:

http://e2e.ti.com/support/amplifiers/precision_amplifiers/f/14/t/161153.aspx

http://www.en-genius.net/site/zones/audiovideoZONE/technical_notes/avt_030110

I strongly suggest you read through these and take the advice provided to contact the hydrophone manufacturer to determine if they recommend voltage vs. charge amplification. After that you can consult some of the example circuits for ideas once you've decided what methods you'll use.

On the same subject, I successfully used hydrophone sensors from Reson when I was in college for a SONAR application for our submarine that competed in the AUVSI DARPA challenge. We chose to use a model that included a pre-amplifier (JFET) packaged with the hydrophone. It allowed for much easier acquisition of the hydrophone signals and allowed for simple voltage-mode gain and filtering similar to what is shown in the article for the microphone amplifier circuit. You may consider a model with a pre-amp included as well.

Regards,
Collin Wells
Precision Linear Applications

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amplifier for hydrophone(use of giga ohm resistor in circuit)