WM8721

Product Preview

WOLFSON MICROELECTRONICS LTD

PP Rev 1.3 November 2000

23

USB MODE SAMPLE RATES

In USB mode the MCLK input is 12MHz only.

SAMPLING

RATE

DAC

MCLK

FREQUENCY

SAMPLE

RATE

REGISTER SETTINGS

DIGITAL

FILTER

TYPE

KHz

MHz

BOSR

SR3

SR2

SR1

SR0

48

12.000

0

0

0

0

0

0

44.1 (Note 2)

12.000

1

1

0

0

0

1

8

12.000

0

0

0

0

1

0

8 (Note 1)

12.000

1

1

0

0

1

1

32

12.000

0

0

1

1

0

0

96

12.000

0

0

1

1

1

3

88.2 (Note 3)

12.000

1

1

1

1

1

2

Table 13 USB Mode Sample Rate Look-up Table

Notes:

1.

8k not exact, actual = 8.021kHz

2.

44.1k not exact, actual = 44.118kHz

3.

88.1k not exact, actual = 88.235kHz

4.

All other combinations of BOSR and SR[3:0] that are not in the truth table are invalid

The BOSR bit represents the base over-sampling rate. This is the rate that the WM8721 digital signal

processing is carried out at and the sampling rate will always be a sub-multiple of this. In USB mode,

with BOSR = 0, the base over-sampling rate is defined at 250Fs, with BOSR = 1, the base over-

sampling rate is defined at 272Fs. This can be used to determine the actual audio sampling rate

required by the DAC.

The exact sample rates supported for all combinations are defined by the relationships in Table 14

below.

ACTUAL SAMPLING RATE

TARGET

SAMPLING

RATE

BOSR=0

( 250FS)

BOSR=1

(272FS)

KHz

KHz

KHz

8

8.021

8

12MHz/(250 x 48/8)

12MHz/(272 x 11/2)

32

32

12MHz/(250 x 48/32)

not available

44.117

44.1

not available

12MHz/272

48

48

12MHz/250

not available

88.235

88.2

not available

12MHz/136

96

96

12MHz/125

not available

Table 14 USB Mode Actual Sample Rates