AD1939 CODEC sample rate

SigmaDSP & SigmaStudio DKF638 Mar 25, 2020 00:00 2 replies Original on forum ↗

ICs: AD1939

DKF638 Question

Mar 25, 2020 00:00

For the AD1939 CODEC, data sheet specifies sample rates of 128/176.4/192 kHz if you set control register to '10'. We did that and are at 192 kHz. How do we get 128 kHz instead ? That's the ADC/DAC sample rate we really want. Thanks.

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DaveThib Reply

Mar 26, 2020 00:00

Hello DKF638.

Notice that for each setting there are three sample rates shown.

32/44.1/48kHz

64/88.2/96kHz

128/176.4/192kHz

Note that this register setting only adjusts a divider to divide the master clock.

So here is the list again but with the divider added that divides down from the master clock.

32/44.1/48kHz, MCLK divided by 256

64/88.2/96kHz, MCLK divided by 128

128/176.4/192kHz, MCLK divided by 64

So which of the three sampling rates you get depends on the master clock rate.

If you use a 12.288MHz master clock then the three register settings will give you 48, 96, or 192kHz fs.

So you will need to change the master clock to be 128 x 64 = 8.192MHz.

This is still within the range of the PLL so all you need to do is change the crystal to an 8.192MHz crystal ( or change the master clock source ) and you will be running at 32, 64 or 128kHz sampling rates.