setting sampling rates of an ADC

[haydaa]

aic23 schematic chrystal

Hi,

How does a designer (manufacturer) calibrate, set, arrange sampling rates of an ADC?

How does a user change its sampling frequency?

Added after 1 minutes:

I have been using C6713 DSP starter kit. Various sampling rates can be choosen. Also everybody use sound card and we can record sound at various sampling rates.

How does this happen?

 

[nitu]

aic23 in 16khz

Hi..
If I am able to understand correctly, you are asking how to decide sampling rate.
It depends upon the frequency and bandwidth of the signal. As per NYQUIST criteria you need to have sampling rate atleast two times the maximum frequency of signal which is going to be sampled.

I hope it helps..

 

[haydaa]

My question is not related the Nyquist rate or antialiasing.

My question is related ADC's operating frequency setting. How can you sample a signal 8 kHz instead 16 khz? By choosing 16 kHz what are changed? I think one of them may be clock frequency

 

[RegUser_2]

My question is not related the Nyquist rate or antialiasing.

My question is related ADC's operating frequency setting. How can you sample a signal 8 kHz instead 16 khz? By choosing 16 kHz what are changed? I think one of them may be clock frequency

Your question is EXACTLY related to the Nyquist rate. The ADC sampling rate have to be higher than the Nyquist rate, so the original signal could be reconstructed correctly.

Regarding HOW to set an ADC sampling rate, it dependes on the ADC type. Most SAR ADC have START convert to initiate conversion (which takes N ADC CLK periods, where N is the ADC resolution and the ADC CLK is fast internal ADC clock). When the conversion is doine and the result is settled in the SAR register, the ADC sets a RDY flag to inform you to take the data.

So in this case, it's entirely up to you how fast YOU want to initiate conversion (what is the ADC sampling rate).

In other classes like for instance the Sigma-Delta modulators, it is advantageous to let the ADC free running and have it interrupt your processor when the data is ready. naturally the ADC sampling in this case is set when the ADC got initialized.


In your case the kit is equiped with TLV320AIC23. So read the manual : https://www.ti.com/lit/gpn/tlv320aic23



The TLV320AIC23 is a high-performance stereo audio codec with highly integrated analog functionality. The analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) within the TLV320AIC23 use multibit sigma-delta technology with integrated oversampling digital interpolation filters. Data-transfer word lengths of 16, 20, 24, and 32 bits, with sample rates from 8 kHz to 96 kHz, are supported. The ADC sigma-delta modulator features third-order multibit architecture with up to 90-dBA signal-to-noise ratio (SNR) at audio sampling rates up to 96 kHz, enabling high-fidelity audio recording in a compact, power-saving design. The DAC sigma-delta modulator features a second-order multibit architecture with up to 100-dBA SNR at audio sampling rates up to 96 kHz, enabling high-quality digital audio-playback capability, while consuming less than 23 mW during playback only. The TLV320AIC23 is the ideal analog input/output (I/O) choice for portable digital audio-player and recorder applications, such as MP3 digital audio players.

Integrated analog features consist of stereo-line inputs with an analog bypass path, a stereo headphone amplifier, with analog volume control and mute, and a complete electret-microphone-capsule biasing and buffering solution. The headphone amplifier is capable of delivering 30 mW per channel into 32 . The analog bypass path allows use of the stereo-line inputs and the headphone amplifier with analog volume control, while completely bypassing the codec, thus enabling further design flexibility, such as integrated FM tuners. A microphone bias-voltage output provides a low-noise current source for electret-capsule biasing. The AIC23 has an integrated adjustable microphone amplifier (gain adjustable from 1 to 5) and a programmable gain microphone amplifier (0 dB or 20 dB). The microphone signal can be mixed with the output signals if a sidetone is required.

While the TLV320AIC23 supports the industry-standard oversampling rates of 256 fs and 384 fs, unique oversampling rates of 250 fs and 272 fs are provided, which optimize interface considerations in designs using TI C54x digital signal processors (DSPs) and universal serial bus (USB) data interfaces. A single 12-MHz crystal can supply clocking to the DSP, USB, and codec. The TLV320AIC23 features an internal oscillator that, when connected to a 12-MHz external crystal, provides a system clock to the DSP and other peripherals at either 12 MHz or 6 MHz, using an internal clock buffer and selectable divider. Audio sample rates of 48 kHz and compact-disc (CD) standard 44.1 kHz are supported directly from a 12-MHz master clock with 250 fs and 272 fs oversampling rates.

Low power consumption and flexible power management allow selective shutdown of codec functions, thus extending battery life in portable applications. This design solution, coupled with the industry’s smallest package, the TI proprietary MicroStar Junior™ using only 25 mm2 of board area, makes powerful portable stereo audio designs easily realizable in a cost-effective, space-saving total analog I/O solution: the TLV320AIC23.

 

[haydaa]

Hi RegUser_2

You said "it's entirely up to you how fast YOU want to initiate conversion (what is the ADC sampling rate)." I need, search, want this.

If you have detailed documents or web sites or something about this. Please share it.

Added after 10 minutes:

AIC23 can sample at 8, 16, 24, 32, 44.1 48, 96 kHz.

I need higher. I have searched ADC daughtercards. Like AIC23, their ADC's operate at predefined frequency. Generally it is mentioned about only highest freq.

1.If I want to sample any other rate? How can I do this?

2. If I want to design an ADC itself; How can I set its operating,sampling frequency?

 

[RegUser_2]

Hi RegUser_2

You said "it's entirely up to you how fast YOU want to initiate conversion (what is the ADC sampling rate)." I need, search, want this.

If you have detailed documents or web sites or something about this. Please share it.

Added after 10 minutes:

AIC23 can sample at 8, 16, 24, 32, 44.1 48, 96 kHz.

I need higher. I have searched ADC daughtercards. Like AIC23, their ADC's operate at predefined frequency. Generally it is mentioned about only highest freq.

1.If I want to sample any other rate? How can I do this?

2. If I want to design an ADC itself; How can I set its operating,sampling frequency?

Like I said, read the USER MANUAL https://www.ti.com/lit/gpn/tlv320aic23

page 3-9

3.3.2 Audio Sampling Rates

The TLV320AIC23 can operate in master or slave clock mode. In the master mode, the TLV320AIC23 clock and sampling rates are derived from a 12-MHz MCLK signal. This 12-MHz clock signal is compatible with the USB specification. The TLV320AIC23 can be used directly in a USB system.

In the slave mode, an appropriate MCLK or crystal frequency and the sample rate control register settings control the TLV320AIC23 clock and sampling rates.

The settings in the sample rate control register control the clock mode and sampling rates.

......

It is unlikely you can get ADC sampling rates above the 96 kHz. May be you can up the ADC oscilator frequency to higher, but in your case the codec is part of a system, so I doubt this to be possible.

 

[haydaa]

Hi again RegUser_2,

I will hit "helped me" button for you. You have amplified my thoughts.

I need and want more. Yes, I can control sampling rate by using clock (crystal) frequency. You have supported this idea.

It would be super if there is some circuit diagrams, application examples, detailed explanation of mechanism. So I can understand clearly and apply it in practice easily.

Added after 6 minutes:

From Introduction AIC23:

While the TLV320AIC23 supports the industry-standard oversampling rates of 256 fs and 384 fs, unique oversampling
rates of 250 fs and 272 fs are provided, which optimize interface considerations in designs using TI C54x digital signal
processors (DSPs) and universal serial bus (USB) data interfaces.

In my opininon, This type of knowledges are meaningles without application.

What is fs? Why 250fs 272fs? ...

How can I generate and apply suitable crystal (clock) frequency to the AIC23 or any other ADC?...

 

[RegUser_2]

Hi again RegUser_2,

I will hit "helped me" button for you. You have amplified my thoughts.

I need and want more. Yes, I can control sampling rate by using clock (crystal) frequency. You have supported this idea.

It would be super if there is some circuit diagrams, application examples, detailed explanation of mechanism. So I can understand clearly and apply it in practice easily.

Added after 6 minutes:

From Introduction AIC23:

While the TLV320AIC23 supports the industry-standard oversampling rates of 256 fs and 384 fs, unique oversampling
rates of 250 fs and 272 fs are provided, which optimize interface considerations in designs using TI C54x digital signal
processors (DSPs) and universal serial bus (USB) data interfaces.

In my opininon, This type of knowledges are meaningles without application.

What is fs? Why 250fs 272fs? ...

How can I generate and apply suitable crystal (clock) frequency to the AIC23 or any other ADC?...

250fs 272fs is the operational frequency of the Sigma Delta Modulator (SDM), where fs is the output data sampling rate (ADC sampling frequency).

To understand how this work you should download some e-book with description of the theory and implementation of SDM (for instance ) and educate yourself. Like Aristotel used to say to Phillip the Makedonian who ask him if there's a fast way to learn science for his soon Alexander - "THERE IS NOT KING'S ROAD IN SCIENCE". Want to know more - educate yourself.

 

[haydaa]

You are right.

If you look at my post at 09 Jun 2007 20:16
I have said "If you have detailed documents or web sites or something about this. Please share it."

"Instead re-invention of wheel" some expert person can help to go true and short way. The best guide may to show correct book, to advise correct software, a few keywords or something like this.

A Turkish person (me) says: "SCIENCE WOULDN'T BE DOWNLOADED LIKE HOLLY BOOK; WE HAVE TO SEARCH IT"

You say, "educate yourself". I say "please advise correct way: docs, web sites, books etc".

I believe that It doesn't matter a person KING or SLAVE who want science, reach it definitely. This is guaranteed by ALLAH (GOD). This is part of my religion. I have written this paragraph for some accusation feelings. Please try to set empathy.

 

[RegUser_2]

You are right.

If you look at my post at 09 Jun 2007 20:16
I have said "If you have detailed documents or web sites or something about this. Please share it."

"Instead re-invention of wheel" some expert person can help to go true and short way. The best guide may to show correct book, to advise correct software, a few keywords or something like this.

A Turkish person (me) says: "SCIENCE WOULDN'T BE DOWNLOADED LIKE HOLLY BOOK; WE HAVE TO SEARCH IT"

You say, "educate yourself". I say "please advise correct way: docs, web sites, books etc".

I believe that It doesn't matter a person KING or SLAVE who want science, reach it definitely. This is guaranteed by ----- (---). This is part of my religion. I have written this paragraph for some accusation feelings. Please try to set empathy.

That's why I posted to you links to (i hope) usefull materials to read. Regarding your current problem about the maximuum ADC sampling rate of 96 kHz, I believe it is indded the fastest one you will ever get with this kind of codec. This nimber also is listed in the MAX allawable for this particular codec chip, what means that probabbility to get reliable operation at higher ADC sampling rates falls exponentially.