wm8974gefl-v Wolfson Microelectronics plc, wm8974gefl-v Datasheet - Page 22

• Manufacturer Part Number: wm8974gefl-v
• Description: Mono Codec With Speaker Driver
• Manufacturer: Wolfson Microelectronics plc

WM8974
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NOTCH FILTER WORKED EXAMPLE
DIGITAL ADC VOLUME CONTROL
Table 13 ADC Volume
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
NFn_A0 = -a0 x 213 = -8085 (rounded to nearest whole number)
NFn_A1 = -a1 x 212 = 8069 (rounded to nearest whole number)
These values are then converted to 2’s complement:
NFA0 = 14’h206B = 14’b10000001101011
NFA1 = 14’h1F85 = 14’b 01111110000101
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:
Gain = 0.5 x (x–255) dB for 1 ≤ x ≤ 255, MUTE for x = 0
a
a
w
w
R15
ADC Digital
Volume
1
0
0
b
=
=
REGISTER
ADDRESS
=
=
−
1
1
2
2
1 (
−
+
π
π
f
f
tan(
tan(
+
c
b
f /
f /
a
0
s
s
w
w
)
=
cos(
=
b
b
/
/
2
2
) 2
) 2
π
π
w
7:0
x (100 / 48000) = 0.01308996939 rads
BIT
x (1000 / 48000) = 0.1308996939 rads
=
0
)
1
1
=
−
+
tan(
tan(
−
ADCVOL
[7:0]
1 ( +
. 0
. 0
LABEL
. 0
0130899693
0130899693
9869949627
11111111
( 0dB )
DEFAULT
/ 9
/ 9
)
cos(
) 2
) 2
= 0.9869949627
. 0
1308996939
ADC Digital Volume Control
0000 0000 = Digital Mute
0000 0001 = -127dB
0000 0010 = -126.5dB
… 0.5dB steps up to
1111 1111 = 0dB
)
= -1.969995945
PD, Rev 4.5, September 2008
DESCRIPTION
Production Data
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