10 months, 2 weeks ago.

Sigma Delta ADC

I want to use the RS Audio Codec to capture audio for processing on my LPC1768. It is RS part number 754-1974. It also gets a mention in the cookbook: https://os.mbed.com/cookbook/RS-Audio-Codec.

It uses a Sigma-Delta ADC. What does this mean in a practical sense? Will the data it delivers to the LPC1768 be in a different format from the usual PCM produced by its internal ADCs? If so, how do I convert the Sigma-Delta format into something I can recognise, that will numerically represent the instantaneous voltage on the analogue input pin?

Thanks!

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2 Answers

10 months, 2 weeks ago.

Sigma-Delta ADCs require a digital filter and decimator to reconstruct the analog values at a reasonable frequency. Since your processor probably doesn't include such a filter, you'll have to implement it yourself. Take a look at http://www.ti.com/lit/an/slyt438/slyt438.pdf or search for "delta sigma adc digital filter" and you'll find a lot of information.

Thank you, Ned, that's really interesting. Having read the paper, though, I wonder if the ADC chip might include the filter and decimator onboard:

http://www.ti.com/lit/ds/symlink/tlv320aic23b.pdf

I can't tell from the description - it doesn't seem explicit. However, I can't think what use a Sigma-Delta ADC would be without the filter and decimator, which makes me wonder if it's all in the same package. What do you think?

posted by Steve Thackery 02 Jan 2019
10 months, 2 weeks ago.

Quote:

which makes me wonder if it's all in the same package. What do you think?

Yes, it's all in the same package. If you deep-dive into the datasheet that is on the link you sent you'll find TI's information of how to read the data. The SPI bus will read the data and you will get your 16 -32 bit data out of the ADC. Lots of examples out in cyberspace and on TI's website for this.

Thanks, Bill and Ned, for your assistance. Very much appreciated.

posted by Steve Thackery 03 Jan 2019