WM8976 Wolfson Microelectronics Ltd., WM8976 Datasheet - Page 28

• Manufacturer Part Number: WM8976
• Description: The WM8976 is a low power, high quality stereo codec designed for portable applications such as Digital still camera or Digital Camcorde
• Manufacturer: Wolfson Microelectronics Ltd.

WM8976
w
NOTCH FILTER WORKED EXAMPLE
DIGITAL ADC VOLUME CONTROL
Table 16 ADC Digital Volume Control
The following example illustrates how to calculate the a0 and a1 coefficients for a desired centre
frequency and -3dB bandwidth.
fc = 1000 Hz
fb = 100 Hz
fs = 48000 Hz
1.969995945
NFA0 = -a0 x 213 = -8085 (rounded to nearest whole number)
NFA1 = -a1 x 212 = 8069 (rounded to nearest whole number)
These values are then converted to a 14-bit sign / magnitude notation:
NFA0[13] = 1; NFA0[12:0] = 13’h1F95; NFA0 = 14’h3F95 = 14’b11111110010101
NFA1[13] = 0; NFA1[12:0] = 13’h1F85; NFA1 = 14’h1F85 = 14’b01111110000101
The output of the ADC 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
w
w
a
a
R15
ADC Digital
Volume
0
1
0
b
REGISTER
ADDRESS
(G-255) dB for 1
1
1
2
2
1 (
f
f
tan(
tan(
b
c
/
/
a
f
f
0
s
w
w
s
)
7:0
8
=
=
b
b
BIT
cos(
/
/
2
2
) 2
) 2
G
w
ADCVOLL
[7:0]
ADCVU
x (100 / 48000) = 0.01308996939 rads
x (1000 / 48000) = 0.1308996939 rads
=
0
255;
LABEL
1
1
)
=
tan(
tan(
. 0
. 0
MUTE for G = 0
1 (
0130899693
0130899693
11111111
( 0dB )
Not
latched
DEFAULT
. 0
9869949627
ADC Digital Volume Control
0000 0000 = Digital Mute
0000 0001 = -127dB
0000 0010 = -126.5dB
... 0.5dB steps up to
1111 1111 = 0dB
ADC volume does not update until a 1 is
written to ADCVU
/ 9
/ 9
) 2
) 2
)
= 0.9869949627
cos(
DESCRIPTION
. 0
1308996939
PP Rev 3.0 April 2006
Pre-Production
)
= -
28