ADMP441, SSM2529 Speech transmission

I am constructing a hearing aid for my bachelor degree project. This hearing aid will consist of a microphone with a Nordic Semiconductor nRF2460 2.4 GHz transmitter, and a receiver of samë model with a speaker. This device should filter out any unwanted frequencies outside of speech, that is anything outside of 1-5 kHz. We want to sample at 12 kHz. I and my group are designing the PCB's and power supply ourselves. For simplicity we want mostly digital signals on our PCB's. Therefore we want to use the ADMP441 which has an ADC included with an I2S interface. Our transmitter and receiver (which are the same IC), support 16 bit I2S. The SSM2529 will be our DAC and amplifier stage, and also the filter stage.

The question is, can I use the ADMP441, which supports 24 bit, to send a 16 bit signal to my 16 bit compatible transmitter?

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  • Thank you for a thorough explanation.

    I have looked further at your catalog of op-amps. Since I am designing a portable unit, I examined the following, with 5 V supply:

    AD8605/AD8606/AD8608, AD8691/AD8692/AD8694, AD8655/AD8656, and the ADA4075-2.

    I am very unsure of which of these are best suited.

    The last one was suggested by AD's website as a replacement for the OP275 which was included in the AD1938 datasheet, in the Sallen-Key filter (I am also looking at Delyiannis bandpass filters, for lower cost, more uniform component values). It would appear I don't need more than unity gain and Q=1, but possibly multiple poles.

    Question1: Am I right in assuming that the AD8694 is like the AD8691 only with more op-amps integrated into one? (for prototyping this could be very useful)

    Question2: How crucial is slew rate in this low power, audio application?

    I see the OP275 has a higher slew rate than the AD8694, but this is perhaps because of the different power/voltage rating?

    Thanks for your help.

    regards, Eystein

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  • Thank you for a thorough explanation.

    I have looked further at your catalog of op-amps. Since I am designing a portable unit, I examined the following, with 5 V supply:

    AD8605/AD8606/AD8608, AD8691/AD8692/AD8694, AD8655/AD8656, and the ADA4075-2.

    I am very unsure of which of these are best suited.

    The last one was suggested by AD's website as a replacement for the OP275 which was included in the AD1938 datasheet, in the Sallen-Key filter (I am also looking at Delyiannis bandpass filters, for lower cost, more uniform component values). It would appear I don't need more than unity gain and Q=1, but possibly multiple poles.

    Question1: Am I right in assuming that the AD8694 is like the AD8691 only with more op-amps integrated into one? (for prototyping this could be very useful)

    Question2: How crucial is slew rate in this low power, audio application?

    I see the OP275 has a higher slew rate than the AD8694, but this is perhaps because of the different power/voltage rating?

    Thanks for your help.

    regards, Eystein

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