WM8985_07 WOLFSON [Wolfson Microelectronics plc], WM8985_07 Datasheet - Page 40

• Manufacturer Part Number: WM8985_07
• Description: Multimedia CODEC With Class D Headphone and Line Out
• Manufacturer: WOLFSON [Wolfson Microelectronics plc]

WM8985
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PROGRAMMABLE NOTCH FILTER
Table 17 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. 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.
Where:
f
The actual register values can be determined from the coefficients as follows:
a
The coefficients are calculated as follows:
w
w
c
R27 (1Bh)
Notch Filter 1
R28 (1Ch)
Notch Filter 2
R29 (1Dh)
Notch Filter 3
R30 (1Eh)
Notch Filter 4
1
= centre frequency in Hz, f
0
b
=
REGISTER
ADDRESS
=
=
−
2
2
1 (
π
π
f
f
+
c
b
NFA0 = -a0 x 2
NFA1 = -a1 x 2
a
a
f /
f /
0
0
s
s
)
=
cos(
1
1
−
+
tan(
tan(
w
0
6:0
7
8
6:0
8
6:0
8
0-6
8
)
BIT
w
w
b
b
13
12
/
/
) 2
) 2
b
= -3dB bandwidth in Hz, f
NFA0[13:7]
NFEN
NFU
NFA0[6:0]
NFU
NFA1[13:7]
NFU
NFA1[6:0]
NFU
LABEL
DEFAULT
0
0
0
0
0
0
0
0
0
s
= sample frequency in Hz
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.
DESCRIPTION
PP, Rev 3.5, March 2007
Pre-Production
40