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TLV320AIC3110: Minimum signal level required at the input of analog microphone port

Part Number: TLV320AIC3110

Hi Team,

Our customer would like to know the minimum signal level required at the input of analog mic input port / at the input of the ADC (considering 0dB of pre-amp gain). He need to evaluate whether his microphone will be supported by this device or not.

The Mic sensitivity is around -47 dB (1 Pa) and input SPL to Mic = 60 dBA.

He is planning to use TLV320AIC3110 for interfacing his microphone and need to check the feasibility of using TLV320AIC3110 for the stated application.

Regards,

Danilo

  • Hi Danilo,

    You certainly would like to utilize the full scale of the ADC which is 2Vpp. That being said, for microphone applications, there is an integrated PGA that allows the user to add 59.5dB of gain. In terms of peak to peak levels, I would recommend a minimum of around 2.02mVpp. 

    This is assuming a constant level and I understand that microphones are not generally used to send constant tones. There may be lower levels or higher levels depending on the sound it's picking up. The higher levels would be an issue as they would get amplified and possibly cause some clipping. So some caution needs to be taken to ensure that there will be no clipping if there is a high peak coming through from the microphone with high gain. 

    Regards,

    Aaron Estrada

  • Hi Aaron,

    Thank you for your response. We have received further inquiries from the customer as follows. 

    I still had a couple of queries with reference to your response.

    1. I could not ding 2Vpp as the full scale voltage in the data sheet and hence took 3.3 V as the reference voltage for calculations. (please refer to the attachment)

    2. How did you arrive at 2.02 mVpp value?

    Also, can you please go through the attached file and throw some light on the same?

    Mic interface with TLV320AIC3110.pdf 

    Regards,

    Danilo

  • Hi Danilo,

    2.02mVpp is more of an ideal minimum input level. I arrived at this number simply because the maximum gain applicable at the input is 59.5dB or ~944V/V and you would like to use as much of the input signal possible. Taking gain error into account, you would want the input ~2mVpp.

    (Full Scale Input)/ 944V/V

    This is obviously not going to be ideal with the various microphones out there but if the mic output level is ~89uV, then the max level the ADC will see is 84mVp or 168mVpp (944 * 89uV). This is relatively low level and may require some sort of amplification before reaching the CODEC.  

    Regards,

    Aaron Estrada

  • Hello Aaron,

    Thanks for the calculations breakup. It makes more sense to me now. 

    However, I'm still unable to find this number (2Vpp) in the datasheet. Can you please provide the reference as this would help me understand where to look in the datasheet for my future calculations?

    Also, how shall I involve ADC resolution and SNR into calculations? As introduction of SNR into calculations would modify the numbers upto some extent.

    One more query. Since the minimum signal detectable by the device is 2 mVpp and the signal coming from mic is almost 168 mVpp, why additional amplification is required between mic and CODEC input?

    Thanks.

    Harsh Trivedi

  • Hello Harsh,

    I think there may have been some misunderstanding on my end. The minimum detectable signal by the ADC will in fact be the LSB. The calculation used by you in the .PDF you sent seem to be correct. 

    I think what I am trying to get across is that you generally would like to utilize as much of the ADC as possible. That means using a full scale input. Otherwise you are just wasting bits. That being said, ~2mVpp is the minimum would would want as you can only apply 59.5dB of gain with the PGA. However, that does not mean that 2mVpp is the absolute minimum input level. 

    The 2Vpp full scale input spec can be found in the Electrical Characteristics table. It is spec'd as .707Vrms but is the same as 2Vpp. 

    Regards,

    Aaron Estrada

  • Thanks for the clarification Aaron. I'm still left with some queries, the same are attached as a DOCx file.

    Can you please share your thoughts on the same?

    EM ES TI Query.docx

  • Hi Harsh,

    I have added my comments in red in the document. 

    EM ES TI Query_6_10.docx

    Regards,

    Aaron Estrada

  • Hello Aaron,

    I saw the updated doc. I had all the answers that I was looking for.

    Many thanks for the help.

    Regards,

    Harsh Trivedi