Cirrus Logic WM8940 Manual page 28

28
REGISTER BIT
ADDRESS
R20
15
Notch Filter 2A
14
13:0
R21
15
Notch Filter 2B
13:0
Table 17 Notch Filter 2 Function
REGISTER BIT
ADDRESS
R22
15
Notch Filter 3A
14
13:0
R23
15
Notch Filter 3B
14
13:0
Table 18 Notch Filter 3 Function
The notch filter coefficients must be entered using a sign / magnitude notation.
The MSB of the 14-bit register word (NFx_Ax[13]) is reserved for the sign part, leaving the 13
remaining bits for the magnitude part.
The notch filter coefficients are calculated as follows:
−
1 tan( w
=
b
a
+
0
1 tan( w
b
= − +
a 1 ( a ) cos(
1 0
Where:

=
w 2 f / f
0 c s

=
w 2 f / f
b b s
f = centre frequency in Hz, f
c
LABEL DEFAULT
0
NF2_UP Notch filter 2 update. The notch filter 2
values used internally only update when
one of the NFU bits is set high.
0
NF2_EN Notch filter 2 enable.
0=Disabled
1=Enabled
0
NF2_A0 Notch filter 2 a0 coefficient
0
NF2_UP Notch filter 2 update. The notch filter 2
values used internally only update when
one of the NFU bits is set high.
0
NF2_A1 Notch filter 2 a1 coefficient
LABEL DEFAULT
0
NF3_UP Notch filter 3 update. The notch filter 3
values used internally only update when
one of the NFU bits is set high.
0
NF3_EN Notch filter 3 enable.
0=Disabled
1=Enabled
0
NF3_A0 Notch filter 3 a0 coefficient
0
NF3_UP Notch filter 3 update. The notch filter 3
values used internally only update when
one of the NFU bits is set high.
0
NF3_LP Notch filter 3 mode select
0 = Notch Filter mode
1 = Low Pass Filter mode
0
NF3_A1 Notch filter 3 a1 coefficient
/ ) 2
/ ) 2
w )
0
= -3dB bandwidth in Hz, f
b
WM8940
DESCRIPTION
DESCRIPTION
= sample frequency in Hz
s
Rev 4.4