Query on AIC-23 Codec

Hi All,

   i am going through the datasheet of AIC-23 Codec on TI board, in the
datasheet i have come acrros this statement
         BOSR Base oversampling rate
                             USB mode:    0 = 250 fs 1 = 272 fs
                             Normal mode: 0 = 256 fs 1 = 384 fs
where 0 and 1 are the bit to be set in the BOSR Register.
        My Query is, what actually mean by the 250 * fs and on what
basis they get these values?

Note: the Data sheet is in the following link
                 "http://focus.ti.com/lit/ds/symlink/tlv320aic23b.pdf"
and page number 3-9

please help me out in solving this query,
Rgds
-Prasad

Prasad

>   i am going through the datasheet of AIC-23 Codec on TI board, in the
> datasheet i have come acrros this statement
>         BOSR Base oversampling rate
>                             USB mode:    0 = 250 fs 1 = 272 fs
>                             Normal mode: 0 = 256 fs 1 = 384 fs
> where 0 and 1 are the bit to be set in the BOSR Register.
>        My Query is, what actually mean by the 250 * fs and on what
> basis they get these values?

This is to do with the crystal used for the oscillator. Devices with USB 
connectivity often have a 12MHz crytal source, so to save money on large 
production runs the codec allows you to use a USB crystal oscillator source 
to run the codec.

In USB mode, both PC and CD sampling rates can be derived.

12MHz / 250 = 48kHz (PC standard)
12MHz / 272 ~= 44.1kHz (CD standard)

In Normal mode, other oscillator sources are used such as 12.288MHz to 
derive sample rates such as 48kHz using simple 2^n oversampling rates - see 
section 3.3.2.2 of the AIC pdf document.

Cheers, Howard