WM8940
Pre-Production
HPFCUT
FS (KHZ)
SR=011/010
22.05
SR=101/100
11.025
SR=001/000
44.1
8
12
16
24
32
48
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]. 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
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R16
0
15
14
NF0_UP
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 0 enable:
Notch Filter 0A
0
NF0_EN
0=Disabled
1=Enabled
0
0
13:0
15
NF0_A0
NF0_UP
Notch Filter 0 a0 coefficient
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 0 a1 coefficient
R17
Notch Filter 0B
0
13:0
NF0_A1
Table 15 Notch Filter 0 Function
Pre-Production, Rev 3.0, February 2007
24
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
