xwm8722eds ETC-unknow, xwm8722eds Datasheet - Page 9

• Manufacturer Part Number: xwm8722eds
• Description: Stereo Dac With Integrated Tone Generator And Line/variable Level Outputs
• Manufacturer: ETC-unknow

WM8722
DEVICE DESCRIPTION
ANALOGUE MIXER
WM8722 is a complete low cost stereo audio DAC, including digital interpolation filter, multi-bit sigma
delta with dither, and switched capacitor multi-bit stereo DAC and output smoothing filters. A novel
multi-bit sigma-delta DAC design is used, utilising a 64x oversampling rate, to optimise signal-to-
noise performance and increase clock jitter tolerance. The WM8722 also provides an analogue
mixing function, which allows user-selectable control over mixing of an external analogue input signal
(line level sources or microphone output) with the converted output signal. The device provides both
line level and variable outputs. The WM8722 contains a high performance sine wave generator
circuit, which can be used to generate low distortion sinusoidal waveforms of varying frequency and
amplitude. The WM8722 uses a minimum of external components, with the internally generated mid-
rail references used to provide DC bias of output signals requiring only a single external capacitor for
decoupling purposes.
The WM8722 is controlled through a software control interface. This allows control of variables such
as gain levels through each path, tone frequency and duration, and audio data interface format. The
software control interface may be operated using either a 3-wire (SPI compatible) or 2-wire MPU
interface. Selection of interface format is achieved by monitoring the state of BUSY pin at power up.
In 2-wire mode, the latch pin becomes an address select, allowing two WM8722 devices to be used
on the same bus.
Operation using system clock of 256fs or 384fs is provided, selection between clock rates being
automatically controlled. Alternatively, the user can select the clock rate through the software
interface. Sample rates (fs) from less than 8ks/s to 96ks/s are allowed, provided the appropriate
system clock is input.
Tolerance of asynchronous word clock jitter is provided, the internal signal processing of the device
re-synching to the external LRCIN clock once the phase difference between left-right and system
clocks exceeds half an LRCIN period. During this re-synch period, the oversampling filters either
miss an audio sample, or repeat the last sample value, so minimising the audible effects of this
operation.
The interface supports normal (right justified) and I
formats, in both packed and unpacked forms. (Packed has exactly the number of serial clocks
corresponding to the number of data bits, per LRCIN period). Additionally the device automatically
detects when it is connected to a 16 bit packed data source (32 serial clocks per LRCIN) and
switches automatically into 16 bit mode. 44.1kHz de-emphasis is supported, with frequency scaling if
other sample rates are used.
The tone generator circuit uses a high quality sine weighted DAC, and sophisticated noise shaping
techniques to achieve high quality tones with low noise and spurious tone generation. Using the
nominal master tone clock (TCLK) frequency of 27MHz, any frequency from 1Hz to 32kHz may be
generated in 1Hz increments. The duration of the tone burst may be programmed from 0.1second to
25.5 seconds. The next tone may be pre-programmed during a current tone burst, and is then
loaded, in phase continuous manner at the end of the current tone so allowing continuous generation
of varying frequency.
The device is packaged in a small 5.3mm wide 20-pin SSOP package. Single 3V to 5V supplies may
be used, the output amplitude scaling with absolute supply level. Low supply voltage operation and
low current consumption, the low pin count small package and the analogue mixing features, make
the WM8722 attractive for many consumer audio applications, including VCD, CD, DVD-Audio, set-
top boxes and digital TV. Separate analogue and digital supply pins are provided, allowing 3V
operation of digital and 5V operation of analogue circuits.
The analogue mixer circuits comprise signal paths to allow signal switching and gain adjust for each
of the mixer line-in, DAC output, and tone generator signals. Additionally, mono signals can be
created using the completely flexible switching arrangements, and 6dB attenuation switching circuits.
Individual control bits are provided for each of the 5 switch inputs to each summing stage in the
mixer, each signal path therefore being individually controllable. Any combination of output signal is
therefore permissible. Fixed output level line outputs and volume adjusted variable output level
outputs are provided.
2
S (Philips left justified, one bit delayed) interface
AI Rev 2.1 June 2001
Advanced Information
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