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How to interface Knowles Mic to a preamplifier PGA2500

Rakesh Muralidharan
Expert 2810 points
Other Parts Discussed in Thread: PGA2500, PGA2505, TLV1018, PGA2500EVM, OPA134, INA105, INA163, INA166

2451.WP-23502-P16.pdf

I have an electret mic . Pls find the attachment for details.

Now i want to interface it to a pre amplifier PGA2500 or PGA2505. How to do it??

Do you have any application note for the same?/ Please provide me with sufficient design Note. What should i do to put in an anti aliasing filter between mic and PGA2500. plas suggent some circuit for this purpose too.

Please help.

.

  • 0
    TI__Guru 54556 points

    Hello Rakesh,

    Three terminal Electret microphones typically require the following connections:

    Terminal Red or positive will be typically connected to the required voltage supply through a resistor; looking at the datasheet provided, the device should work with supplies from 1.5V to 10V. Some microphone manufacturers recommend the addition of an RC filter to reduce the noise of the supply.  
    The output terminal should be connected to positive plate of a 2.2uF-4.7uF capacitor to the input of the pre-amplifier. Terminal blue or negative will be connected to GND.  Please see figure below.  The TLV1018 is an amplifier recommended for three-wire analog electret microphones.  Please find  a link for the TLV1018 datasheet below.

    The PGA2500/PGA2505 is a digitally controlled gain analog pre-amplifier that typically finds applications as a front end in high-performance audio ADC's and Mixers.  There are some suggestions/recommendations on the input filter on the PGA2500EVM Users Guide for condenser/dynamic microphones with (or without) Phantom power. 

    If the TLV1018 does not meet your needs; please let me know which are your application requirements and we may suggest another device.

    Thank you and Regards,

    Luis

    http://focus.ti.com/lit/ds/symlink/tlv1018.pdf

    http://focus.ti.com/docs/prod/folders/print/pga2500.html

  • 0 in reply to Luis Chioye
    Expert 2810 points

    Thanks for this detailed reply.

    I wanted to have a mic with High SNR in the order of 68dbA to 70dbA. Now won't the usage of TLV1018 impact the SNR significantly. SNR value of TLV1018 seems to be 61dB. Does it imply that the output signal to noise ratio will be compromised??. i was looking for a solution which will not compromise on SNR. Will you suggest some suitable preamplifier for electret microphone???

     

    Also in our application  mic will be 10cm away from mounting plate.

  • 0 in reply to Rakesh Muralidharan
    TI__Guru 54556 points

    Hi Rakesh,

    I did not find immediately the SNR specification on the datasheet for the microphone provided,  Assuming the SNR is in the order of 70dBA (A-weighting filter) for an electret microphone; the following calculations can be made:

     The mic sensitivity on the datasheet provided is -52dB relative to 1V/0.1 Pa; this corresponds to -32dB relative to 1V/pa.  This means that 1 Pa input  yields 25.11mVrms signal.  The SNR spec is usually tested or specified using a standard 1KHz, 94dB SPL (1Pa input) reference signal with an A-weighting filter.  Using the sensitivity calculations above we could solve for the RMS noise level:

    SNR = 20 log(signal/noise RMS); where signal = 25.11mVrms and SNR=70dB.

    Solving the equation we obtain RMS noise=7.92uVrms. From the RMS noise level, the noise density can be roughly estimated:

    Noise Density (Vn) = Noise RMS/(Square root (BandWidth); approximating the A weighted filter as a rectangle of 15kHz to 400Hz; the noise density is approx:

    Vn=65nV/sqrt(Hz)

    There are a few devices available that may be used as electret microphone preamplifiers connecting the mic  single ended: INA163, INA166 and INA105 could be used.  The OPA134 could be also be configured as an Electret microphone Pre-amp (please refer to attachment).  The PGA2505/PGA2500 will also meet and exceed the noise spec, however, the PGA2505 inputs are DC biased using the VCOMIN pin. I would have to measure the performance with a single-ended signal.

    Please find an attachment with the OPA134 with an electret Mic from a colleagues presentation.

    Thank you and Kind Regards,

    Luis

     0652.Electret Microphone Example Circuit Forum.ppt 

     

     

     

     

     

  • 0 in reply to Luis Chioye
    Prodigy 90 points
    Hi engineer
    I what too learn the “0652.Electret Microphone Example Circuit Forum.ppt ”，but I click the link ，it just shows "You do not have permission to view this directory or page.".Could send me the PPT?

    sincerely