WM8980CGEFL/RV WOLFSON [Wolfson Microelectronics plc], WM8980CGEFL/RV Datasheet - Page 33

• Manufacturer Part Number: WM8980CGEFL/RV
• Description: Stereo CODEC with Speaker Driver and Video Buffer
• Manufacturer: WOLFSON [Wolfson Microelectronics plc]

Pre-Production
w
PROGRAMMABLE NOTCH FILTER
Table 16 Notch Filter Function
NOTCH FILTER WORKED EXAMPLE
A programmable notch filter is provided. This filter has a variable centre frequency and bandwidth,
programmable via two coefficients, a0 and a1. The coefficients must be entered in 2’s complement
notation. 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:
The following example illustrates how to calculate the a0 and a1 coefficients for a desired centre
frequency and -3dB bandwidth.
a
The coefficients are calculated as follows:
w
w
c
R27
Notch Filter 1
R28
Notch Filter 2
R29
Notch Filter 3
R30
Notch Filter 4
= centre frequency in Hz, f
1
0
b
REGISTER
ADDRESS




2
2

1 (

NFA0 = -a0 x 2
NFA1 = -a1 x 2
a
f
f
c
b
0

/
/

a
f
f
0
1
1
s
s
)


cos(
6:0
7
8
6:0
8
6:0
8
0-6
8
tan(
tan(
BIT
13
12
w
w
w
0
b
)
= -3dB bandwidth in Hz, f
b
b
NFA0[13:7]
NFEN
NFU
NFA0[6:0]
NFU
NFA1[13:7]
NFU
NFU
NFA1[6:0]
/
/
) 2
) 2
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 3.8, May 2012
WM8980
33