WM8711BL
Production Data
CLOCKING SCHEMES
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. To allow WM8711BL to be used in a centrally clocked system, the WM8711BL is
capable of either generating this system clock itself or receiving it from an external source as will be
discussed.
For applications where it is desirable that the WM8711BL is the system clock source, then clock
generation is achieved through the use of a suitable crystal connected between the XTI/MCLK input
and XTO output pins (see CRYSTAL OSCILLATOR section).
For applications where a component other than the WM8711BL will generate the reference clock, the
external system Master Clock can be applied directly through the XTI/MCLK input pin with no
software configuration necessary. Note that in this situation, the oscillator circuit of the WM8711BL
can be safely powered down to conserve power (see POWER DOWN section)
CORE CLOCK
The WM8711BL DSP core can be clocked either by MCLK or MCLK divided by 2. This is controlled
by software as shown in Table 6 below.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
0001000
6
CLKIDIV2
0
Core Clock divider select
Sampling
Control
1 = Core Clock is MCLK divides by 2
0 = Core Clock is MCLK
Table 6 Software Control of Core Clock
Having a programmable MCLK divider allows the device to be used in applications where higher
frequency master Clocks are available. For example the device can support 512fs master clocks
whilst fundamentally operating in a 256fs mode.
CRYSTAL OSCILLATOR
The WM8711BL includes a crystal oscillator circuit that allows the audio system’s reference clock to
be generated on the device. This is available to the rest of the audio system in buffered form on
CLKOUT. The crystal oscillator is a low radiation type, designed for low EMI. A typical application
circuit is shown Figure 12.
XTI/MCLK
XTO
Cp
Cp
DGND
DGND
Figure 12 Crystal Oscillator Application Circuit
The WM8711BL crystal oscillator provides an extremely low jitter clock source. Low jitter clocks are a
requirement for high quality audio DACs, regardless of the converter architecture. The WM8711BL
architecture is less susceptible than most converter techniques but still requires clocks with less than
approximately 1ns of jitter to maintain performance. In applications where there is more than one
source for the master clock, it is recommended that the clock is generated by the WM8711BL to
minimise such problems.
PD, Rev 4.2, December 2011
2044
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
