wm8974gefl-v Wolfson Microelectronics plc, wm8974gefl-v Datasheet - Page 21

• Manufacturer Part Number: wm8974gefl-v
• Description: Mono Codec With Speaker Driver
• Manufacturer: Wolfson Microelectronics plc

Production Data
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PROGRAMMABLE NOTCH FILTER
Table 12 Notch Filter Function
A programmable notch filter is provided. This filter has a variable centre frequency and bandwidth,
programmable via two coefficients, a0 and a1. These coefficients should be converted to 2’s
complement numbers to determine the register values. A0 and a1 are represented by the register
bits NFA0[13:0] and NFA1[13:0]. Because these coefficient values require four register writes to
setup there is an NFU (Notch Filter Update) flag which should be set only when all four registers are
setup.
The coefficients are calculated as follows:
Where:
The coefficients are calculated as follows:
These values are then converted to 2’s complement notation to determine the register values.
R27
Notch Filter 1
R28
Notch Filter 2
R29
Notch Filter 3
R30
Notch Filter 4
REGISTER
ADDRESS
f
NFA0 = -a0 x 2
NFA1 = -a1 x 2
a
a
w
w
c
= centre frequency in Hz, f
1
0
0
b
=
=
=
=
1
1
−
2
2
π
π
1 (
−
+
6:0
7
8
6:0
8
6:0
8
6:0
8
f
f
tan(
tan(
c
b
+
BIT
/
/
a
13
12
f
f
0
w
w
s
s
)
b
b
cos(
NFA0[13:7]
NFEN
NFU
NFA0[6:0]
NFU]
NFA1[13:7]
NFU
NFA1[6:0]
NFU
/
/
) 2
) 2
LABEL
w
0
b
)
= -3dB bandwidth in Hz, f
0
0
0
0
0
0
0
0
0
DEFAULT
Notch Filter a0 coefficient, bits [13:7]
Notch filter enable:
0=Disabled
1=Enabled
Notch filter update. The notch filter
values used internally only update when
one of the NFU bits is set high.
Notch Filter a0 coefficient, bits [6:0]
Notch filter update. The notch filter
values used internally only update when
one of the NFU bits is set high.
Notch Filter a1 coefficient, bits [13:7]
Notch filter update. The notch filter
values used internally only update when
one of the NFU bits is set high.
Notch Filter a1 coefficient, bits [6:0]
Notch filter update. The notch filter
values used internally only update when
one of the NFU bits is set high.
s
= sample frequency in Hz
PD, Rev 4.5, September 2008
DESCRIPTION
WM8974
21