TLV320AIC3262 Audio Codec - microphone noise

Hank Sun

Prodigy 90 points

Dear All

Our customers say that quality of our headset-microphone is not good.

They can hear a lot of noise.

What can I do to reduce this noise? Modify my layout or schematic?

Thanks~

Dear J

Thanks a lot!!

I modify schematic.

I will place the mic & micbias in a clean GND layer and with GND trace.

Will the mic quality be better if I change to use mic differential input (IN1L/IN1R) ?

Thank you very much!!

Dear J

Thanks a lot~~

As your links,

"Sensitive signals use differential"

"Place 33pF caps from each input to GND"

"Route the signal between ground planes and shield with GND"

but my earphone jack is not a "differential microphone" I modify my sch as follow jpg.

Would you please help us to check?

Thank you very much!!

Dear J

We had modified our sch as follow JPG.

Would you please help us to check it?

Thank you very much!!

over 10 years ago

0 J- over 10 years ago

TI__Mastermind 46195 points

Hi Hank,

First program Page 1, Register 51 = 0xC0 to make sure the headset detection mechanism is not causing issues.

Please refer to this wiki page: e2e.ti.com/.../530.microphone-noise-and-audio-codecs

A spectrum of the DOUT data can help you determine if it is microphone noise or board noise. If it looks like white noise, then the wiki above can help. If it looks like tones, then it might be related to PCB. The main idea is that microphone ground must be at the same potential as AVSS when it comes to parasitics. Also, it is good practice to route the MICBIAS and mic signal between ground plane layers with ground traces next to the mic signals and bias for best immunity. Another alternative is to split the 2.2k resistor into 1.2k and 1k. Then, if mic is far away, place a small capacitor (e.g. 10nF) between 1.2k and 1k resistor, close to the mic. But again, if proper layout is observed, then this is not necessary.

Regards,
J-

0 Hank Sun over 10 years ago in reply to J-

Prodigy 90 points

Thank you very much!!
I modify schematic but I can not attached JPG in this reply.
So I post it in my first topic. Would you please help me to check it?
Thanks a lot!!

0 J- over 10 years ago in reply to Hank Sun

TI__Mastermind 46195 points

Hank,

Doing pseudo-differential will help if the issue is pcb noise coupling and if voltage between AVss and jack ground is a bit different.

The goal is to have the mic ground be the same as AVSS. If not possible, connect negative terminal of differential input to mic ground.

Regards,

J-

0 Hank Sun over 10 years ago in reply to J-

Prodigy 90 points

Thank you very much!
Would you please help me how to design pseudo-differential in my schematic?
Thanks a lot!!!

0 J- over 10 years ago in reply to Hank Sun

TI__Mastermind 46195 points

Hank,

See section 13.2 of this datasheet: www.ti.com/.../tlv320aic3254

Basically, minus input is ac-coupled to ground close to headset jack. Both + and - traces should be routed next to each other (parallel).

Regards,

J-

0 Hank Sun over 10 years ago in reply to J-

Prodigy 90 points

Thanks a lot!!

Do you have the reference design of pseudo differential?

We will change the mic from single-end to pseudo differential at our next version of sch.

Thank you very much!!

0 J- over 10 years ago in reply to Hank Sun

TI__Mastermind 46195 points

Hank,

Page 26 of www.ti.com/.../slaa404, but with upper resistor = 2.2k and lower 1k resistor as 0-ohm because same ground is used by headset speakers.

Regards,

J-

0 Hank Sun over 10 years ago in reply to J-

Prodigy 90 points

Thank you very much!!
I post my sch at my first question. Would you please help me to check it?
Thanks a lot!!

0 J- over 10 years ago in reply to Hank Sun

TI__Mastermind 46195 points

Hank,

IN1R should NOT be connected to ground directly.

You can connect the (-) input pin to 1uF and then to CN1.4. The (-) pin can be IN2R or IN3R if feeding the signal to the left ADC.

Regards,

J-

0 Hank Sun over 10 years ago in reply to J-

Prodigy 90 points

Dear J~
I post our sch at my first question.
Would you please help us to check it?
Thank you very much!!

0 J- over 10 years ago in reply to Hank Sun

TI__Mastermind 46195 points

Hank,

The schematic is incorrect. As I mentioned:

"You can connect the (-) input pin to 1uF and then to CN1.4. The (-) pin can be IN2R or IN3R if feeding the signal to the left ADC."

So use IN1L for mic signal, but IN2R ac-coupled to ground.

Regards,
J-

0 J- over 10 years ago in reply to J-

TI__Mastermind 46195 points

See image below...

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TLV320AIC3262 Audio Codec - microphone noise