WM8738
Production Data
AUDIO DATA SAMPLING RATES
In a typical digital audio system there is only one central clock source producing a reference clock to
which all audio data processing is synchronised. This clock is often referred to as the audio system’s
Master Clock. The external master system clock can be applied directly through the MCLK input pin.
In a system where there are a number of possible sources for the reference clock it is recommended
that the clock source with the lowest jitter be used to optimise the performance of the ADC.
The master clock for WM8738 supports audio sampling rates from 256fs to 768fs, where fs is the
audio sampling frequency LRCLK, typically 32kHz, 44.1kHz, 48kHz, or 96kHz. The master clock is
used to operate the digital filters and the noise shaping circuits.
The WM8738 has a master clock detection circuit that automatically determines the relationship
between the master clock frequency and the sampling rate (to within +/- 32 system clocks). If there is
a greater than 32 clocks error the interface is disabled and maintains the output level at the last
sample. The master clock must be synchronised with LRCLK, although the WM8738 is tolerant of
phase variations or jitter on this clock. Table 1 shows the typical master clock frequency inputs for
the WM8738.
If MCLK is stopped for greater than 10us then the device will enter a low power mode where the
current taken from AVDD is greatly reduced. Note that when the device enters this mode the
references are powered down.
Table 1 shows the common MCLK frequencies for different sample rates.
SAMPLING
RATE
Master Clock Frequency (MHz)
256fs
384fs
512fs
768fs
(LRCLK)
32kHz
8.192
11.2896
12.288
24.576
12.288
16.9340
18.432
36.864
16.384
22.5792
24.576
24.576
33.8688
36.864
44.1kHz
48kHz
96kHz
Unavailable Unavailable
Table 1 Master Clock Frequency Selection
PD Rev 4.4 August 2006
13
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
