WM8978 Wolfson Microelectronics Ltd., WM8978 Datasheet - Page 37
![no-image](/images/no-image-200.jpg)
WM8978
Manufacturer Part Number
WM8978
Description
The WM8978 is a low power, high quality stereo codec designed for portable applications such as Digital still camera or Digital Camcorde
Manufacturer
Wolfson Microelectronics Ltd.
Datasheet
1.WM8978.pdf
(108 pages)
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
WM8978CGEFL/RV
Manufacturer:
WOLFSON
Quantity:
10 000
Part Number:
WM8978CGEFL/RV
Manufacturer:
WOLFSON
Quantity:
20 000
Company:
Part Number:
WM8978G
Manufacturer:
SANYO
Quantity:
87 018
Part Number:
WM8978G
Manufacturer:
WM
Quantity:
20 000
Part Number:
WM8978GEFL
Manufacturer:
WOLFSON
Quantity:
20 000
Company:
Part Number:
WM8978GEFL/RV
Manufacturer:
WOLFSON
Quantity:
9 870
Preliminary Technical Data
w
PROGRAMMABLE NOTCH FILTER
Table 18 Notch Filter Function
DIGITAL ADC VOLUME CONTROL
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:
The output of the ADCs can be digitally attenuated over a range from –127dB to 0dB in 0.5dB steps.
The gain for a given eight-bit code X is given by:
0.5
The coefficients are calculated as follows:
a
w
w
c
R27
Notch Filter 1
R28
Notch Filter 2
R29
Notch Filter 3
R30
Notch Filter 4
1
= centre frequency in Hz, f
0
b
REGISTER
ADDRESS
(G-255) dB for 1
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
G
13
12
w
w
w
0
b
255;
)
b
b
= -3dB bandwidth in Hz, f
NFA0[13:7]
NFEN
NFU
NFA0[6:0]
NFU
NFA1[13:7]
NFU
NFA1[6:0]
NFU
/
/
) 2
) 2
LABEL
MUTE for G = 0
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.
PTD Rev 2.6 November 2005
DESCRIPTION
WM8978
37