Programmable Notch Filters - Cirrus Logic WM8940 Manual

HPF Output
Notch Filter 0
Figure 11 Labelling of Notch Filters and Arrangement of Notch Filter Enables
Rev 4.4

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 1
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.
NF0_EN NF1_EN
Notch Filter 1
The notch filter coefficients must be entered using a sign / magnitude notation.
REGISTER BIT
ADDRESS
R16
15
Notch Filter 0A
14
13:0
R17
15
Notch Filter 0B
13:0
Table 15 Notch Filter 0 Function
REGISTER BIT
ADDRESS
R18
15
Notch Filter 1A
14
13:0
R19
15
Notch Filter 1B
13:0
Table 16 Notch Filter 1 Function
NF2_EN
Notch Filter 2
LABEL DEFAULT
0
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.
0
NF0_EN Notch filter 0 enable:
0=Disabled
1=Enabled
0
NF0_A0 Notch filter 0 a0 coefficient
0
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.
0
NF0_A1 Notch filter 0 a1 coefficient
LABEL DEFAULT
0
NF1_UP Notch filter 1 update. The notch filter 1
values used internally only update when
one of the NFU bits is set high.
0
NF1_EN Notch filter 1 enable.
0=Disabled
1=Enabled
0
NF1_A0 Notch filter 1 a0 coefficient
0
NF1_UP Notch filter 1 update. The notch filter 1
values used internally only update when
one of the NFU bits is set high.
0
NF1_A1 Notch filter 1 a1 coefficient
WM8940
NF3_LP NF3_EN
To Audio
Notch Filter 3
Interface
(or low pass)
DESCRIPTION
DESCRIPTION
st
order
27