• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 31 subscribers
  • Views 370 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TAA3020: AC Coupled TRS Microphone Connection

Peter Frost
Prodigy 30 points

Part Number: TAA3020

Hi,

I have a few question about designing an AC coupled mic input:

  1. As you can see, I'm trying to use the summing feature of the TAA3020 to get slightly better performance. Firstly, does the way I've connected this make sense? Also, is the impedance halved in this configuration, i.e. would a 10K input impedance setting result in an effective input impedance of 5K?
  2. App note SBAA583 www.ti.com/.../sbaa583.pdf has a section on page 16 that says "open circuit voltage of the microphone is VMic. To prevent this loading, maintain Zin >>R." Could you explain this section a bit more? I don't really understand which "loading" this is reffering to, and why Zin greater than R prevents this?
  3. I've struggled to find a good answer on the correct connections for a TRS microphone. Some sources suggest Tip is signal, Ring should be bias, and Sleeve ground. Then I found Sennheiser wire their microphones as Tip is signal, and Ring and Sleeve both grounded (https://docs.cloud.sennheiser.com/en-us/ew-g4/ew-g4/specifications-pin.html), so applying bias to the Ring connection seems like a bad idea in that configuration? I've just left Ring disconnected for now. Does anyone have any experience designing a similar system that could offer advice?

Many thanks, schematic below (MICBIAS is decoupled MICBIAS output from the chip):

image.png

  • 0
    TI__Mastermind 22736 points

    Hi Peter,

    1. Yes, this is how to connect for channel summation, and yes, the input impedance should halve.

    2. I believe this is meant to say make sure Zin >> Ro. This is to ensure the output impedance of the microphone does not load the ADC, which would decrease the voltage at the input pins of the device.

    3. Typically, you would connect the Ring to the minus channel, but since you are using single-ended you can short to GND as well as Sleeve.

    Best,

    Garret

  • 0 in reply to Garret Godfrey
    Prodigy 30 points

    Hi Garret,

    Thanks very much for the clarification.

    Good point about single-ended, would a differential input config work if a "single-ended" microphone was plugged in? I.e. if only Tip had signal, and Ring and Sleeve were both internally ground? Or does the differential input config need a proper 3-pin differential-output microphone?

    Would this be the right connections for differential input? sbaa583 doesn't seem to say explicitly what the pull down (R79) should be, but I assume just equal value to the bias resistor?

    Thanks,

    Peter

  • +1 in reply to Peter Frost
    TI__Mastermind 22736 points

    Hi Peter,

    Peter Frost said:
    would a differential input config work if a "single-ended" microphone was plugged in?

    Depends on what you mean by "work". The differential input config would "work" with a single-ended mic in that it would still output a signal, but full-scale inputs would output at -6dB. You can easily switch this to single-ended config via software.

    Yes, that is correct differential connection. You are correct that R79=R78.

    Best,

    Garret

  • 0 in reply to Garret Godfrey
    Prodigy 30 points

    Hi Garret,

    Yep that makes sense, thanks again for the help.

    Peter