Pre Production
WM8941
HPFCUT
FS (KHZ)
SR=101/100
SR=011/010
SR=001/000
44.1 48
8
11.02
5
12
16
22.0
5
24
32
000
001
010
011
100
101
110
111
82
113
141
180
225
281
360
450
563
122
153
156
245
306
392
490
612
82
113
141
180
225
281
360
450
563
122
153
156
245
306
392
490
612
82
113
141
180
225
281
360
450
563
122
153
156
245
306
392
490
612
102
131
163
204
261
327
408
102
131
163
204
261
327
408
102
131
163
204
261
327
408
Table 14 High Pass Filter Cut-off Frequencies (HPFAPP=1)
Note that the High Pass filter values (when HPFAPP=1) work on the basis that the SR register bits
are set correctly for the actual sample rate as shown in Table 14.
PROGRAMMABLE NOTCH FILTERS
Four programmable notch filters are provided. These filters have a programmable centre frequency
and bandwidth, programmable via two coefficients, a0 and a1. a0 and a1 are represented by the
register bits NFx_A0[13:0] and NFx_A1[13:0]. The notch filter coefficients should be converted to
sign / magnitude notation to enter into the registers. Notch Filter 3 can also be programmed as a 1st
order low pass filter.
Because these coefficient values require two register writes to set up there is an NFx_UP (Notch
Filter Update) flag for each filter which should be set only when both A0 and A1 for the filter have
been set.
The notch filters can be individually enabled, using the corresponding NFx_EN register bit, as can be
seen in Figure 11:
Figure 11 Labelling of Notch Filters and Arrangement of Notch Filter Enables
The notch filter coefficients must be entered using a sign / magnitude notation.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R16
15
14
NF0_UP
0
Notch filter 0 update. The notch filter 0
values used internally only update when
one of the NF0_UP bits is set high.
Notch Filter 0A
NF0_EN
0
Notch filter 0 enable:
0=Disabled
1=Enabled
13:0
15
NF0_A0
NF0_UP
0
0
Notch Filter 0 a0 coefficient
R17
Notch filter 0 update. The notch filter 0
values used internally only update when
one of the NF0_UP bits is set high.
Notch Filter 0B
13:0
NF0_A1
0
Notch Filter 0 a1 coefficient
Table 15 Notch Filter 0 Function
PP, Rev 3.3, December 2007
27
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
