WM8737L
Production Data
Figure 7 ADC Digital Filter
The ADC digital filters contain a digital high pass filter, selectable via software control. The high-pass
filter response is detailed in the “Digital Filter Characteristics” section. When the high-pass filter is
enabled the dc offset is continuously calculated and subtracted from the input signal. By setting
HPOR, the last calculated d.c. offset value is maintained but still subtracted from the input.
The output data format can be programmed by the user to accommodate stereo or monophonic
recording on both inputs. The polarity of the output signal can also be changed under software
control. The software control is shown below.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R5 (05h)
ADC Control
0
4
ADCHPD
0
ADC High Pass Filter Enable (Digital)
1: Disable High Pass Filter
0: Enable High Pass Filter
Store dc offset
HPOR
0
0: Present offset maintained
1: Continuously update offset
00: Polarity not inverted
01: L polarity invert
6:5
POLARITY
00
10: R polarity invert
11: L and R polarity invert
Table 10 ADC Control
ADC MAXIMUM OUTPUT CODES
The ADC output codes are limited by the digital gain of the stage following the 3D enhancement
filters. This limits the max full scale positive output to 7F7FFFh and full scale negative to 808000h. To
get the maximum positive output code (7FFFFFh) and negative code (800000h) from the ADC, the 3D
enhancement filters should be bypassed. This can be done by first setting register R13 (0Dh) to
1_110x_xxxx (1C0h), where x_xxxx represents the required values for the ALC in the application, and
then setting register R28 (1Ch) to 0_0000_0100 (004h).
Note that the above sequence uses test bits that are not documented and the use of these test bits,
other than as described above, is not recommended and is not supported.
3D STEREO ENHANCEMENT
The WM8737L has a 3D stereo enhancement function for use in applications where the natural
separation between stereo channels is low. The function is activated by the 3DEN bit, and artificially
increases the separation between the left and right channels. The 3DDEPTH setting controls the
degree of stereo expansion. Additionally, one of four filter characteristics can be selected for the 3D
processing, using the 3DFILT control bits.
When 3D enhancement is enabled (and/or the tone control for playback) it may be necessary to
attenuate the signal by 6dB to avoid limiting. This is a user selectable function, enabled by setting
DIV2.
PD, Rev 4.4, January 2012
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
