Compiler: electret condesor mic Preamp recommendation

Hi V Pot,

TIDU-765 describes an electret microphone amplifier using the OPA172. You might also want to look at Figure 60 in the OPA1692 datasheet. 

For general information on noise in op amp circuits, consider looking at our TI Precision Lab series on noise, which can be found here.

Alex,

I’ve already looked into that implementation. As said in my post abovd I’m looking for a low noise opamp that was designed to work with supply lower than 3.3v. I’m more interested in antialiasing filter filtering off anything above 4000hz. Rather than preamp because I’m gonna pass this to an adc with 8000hz sampling rate and it has preamp inside it which I’ll use it.

So please recommend a good low noise opamp implementation with supply below 3.3v

Hi V Pot,
You might want to consider OPA320 or TLV6741.

The exact meaning of low noise is going to depend on your circuit configuration. A bipolar input op amp with very low voltage noise may have significant current noise, which will dominate the noise performance of many amplifier circuits. CMOS or FET input op amps can achieve relatively low voltage noise, but typically have very low current noise, so may work better in a transimpedance amplifier like that in TIDU-765.

Alex,

1)Thankyou. Opa320 looks promising for connecting to adc. Does the other opamp can also drive the adc? I’m using aic3206 codec.

2) is there a good antialiasing low pass filter circuit with opa320 or similar for reference?

V Pot,
You might consider following the design provided in SPRAB38A:

www.ti.com/.../sprab38a.pdf

Alex,
Thanks for the doc. My implementation is also stethoscope and I’ve seen this doc before. Can you please clarify below
1) on page 7 figure 6 . What is that NO-0e and NC-0e? Also what is mic_L1 and mic_L_in ?

2) I’m planning to use the pga inside the codec to preamplify. So it is ok to apply lowpass filter then preamplify? Usually people do the other way around right? Any disadvantage?

Alex,

Can you reply to my above question?

V Pot,
It appears that both should be labeled NC 0E, which appears to be a Not-Connected or Do Not Populate component, judging by the schematics further on in the document.

For good noise performance, it would be better to put as much of your signal gain as early as possible in your signal chain. Otherwise, you will have noise from your microphone interface and low pass filter getting gained up (possibly significantly) by the codec PGA. Aside from the noise consideration, I don't think there are any other issues associated with that configuration.

Sorry i have a follow up question to what alex said.

If that is no connection what they meant by nc-0E, then what should i connect to pin 4 in- like it shown in picture of the document for low pass filter schematic