WM8978 Wolfson Microelectronics Ltd., WM8978 Datasheet - Page 44

• Manufacturer Part Number: WM8978
• Description: The WM8978 is a low power, high quality stereo codec designed for portable applications such as Digital still camera or Digital Camcorde
• Manufacturer: Wolfson Microelectronics Ltd.

WM8978
w
AUTO-MUTE
DIGITAL HI-FI DAC VOLUME (GAIN) CONTROL
Table 24 DAC Digital Volume Control
Note: An additional gain of up to +12dB can be added using the gain block embedded in the
digital peak limiter circuit (see DAC OUTPUT LIMITER section).
5-BAND EQUALISER
3-D ENHANCEMENT
DAC DIGITAL OUTPUT LIMITER
The DAC output phase defaults to non-inverted. Setting DACPOLL will invert the DAC output phase
on the left channel and DACPOLR inverts the phase on the right channel.
The DAC has an auto-mute function which applies an analogue mute when 1024 consecutive zeros
are detected. The mute is released as soon as a non-zero sample is detected. Automute can be
disabled using the AMUTE control bit.
The signal volume from each Hi-Fi DAC can be controlled digitally. The gain and attenuation range
is –127dB to 0dB in 0.5dB steps. The level of attenuation for an eight-bit code X is given by:
0.5
A 5-band graphic equaliser function which can be used to change the output frequency levels to suit
the environment. This can be applied to the ADC or DAC path and is described in the 5-BAND
EQUALISER section for further details on this feature.
The WM8978 has an advanced digital 3-D enhancement feature which can be used to vary the
perceived stereo separation of the left and right channels. Like the 5-band equaliser this feature can
be applied to either the ADC record path or the DAC playback path but not both simultaneously.
See the 3-D STEREO ENHANCEMENT section for further details on this feature.
The WM8978 has a digital output limiter function. The operation of this is shown in Figure 22. In
this diagram the upper graph shows the envelope of the input/output signals and the lower graph
shows the gain characteristic.
R11
Left DAC
Digital Volume
R12
Right DAC
Digital Volume
REGISTER
ADDRESS
(X-255) dB for 1
7:0
8
7:0
8
BIT
X
DACVOLL
[7:0]
DACVU
DACVOLR
[7:0]
DACVU
255;
LABEL
MUTE for X = 0
11111111
( 0dB )
Not
latched
11111111
( 0dB )
Not
latched
DEFAULT
Left DAC Digital Volume Control
0000 0000 = Digital Mute
0000 0001 = -127dB
0000 0010 = -126.5dB
... 0.5dB steps up to
1111 1111 = 0dB
DAC left and DAC right volume do
not update until a 1 is written to
DACVU (in reg 11 or 12)
Right DAC Digital Volume Control
0000 0000 = Digital Mute
0000 0001 = -127dB
0000 0010 = -126.5dB
... 0.5dB steps up to
1111 1111 = 0dB
DAC left and DAC right volume do
not update until a 1 is written to
DACVU (in reg 11 or 12)
PTD Rev 2.6 November 2005
DESCRIPTION
Preliminary Technical Data
44