WM8985GEFL Wolfson Microelectronics, WM8985GEFL Datasheet - Page 41

• Manufacturer Part Number: WM8985GEFL
• Description: Audio CODECs Multimedia CODEC with Class D HP
• Manufacturer: Wolfson Microelectronics

Specifications of WM8985GEFL

• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: QFN-32
• Minimum Operating Temperature: - 25 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Production Data
w
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. 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.
Where:
f
The coefficients are calculated as follows:
These values are then converted to 2’s complement notation to determine the register values.
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
PD, Rev 4.6, July 2009
WM8985
41