wm8940gefl-v Wolfson Microelectronics plc, wm8940gefl-v Datasheet - Page 84

• Manufacturer Part Number: wm8940gefl-v
• Description: Mono Codec With Speaker Driver
• Manufacturer: Wolfson Microelectronics plc

WM8940
Figure 48 Cumulative Notch + Low Pass Filters Responses (48kHz);
NF0 fc = 1kHz; NF1 fc = 5kHz; NF2 fc = 10kHz; LPF fc = 11kHz; fb = 100Hz, 600Hz, 2kHz
The following example illustrates how to calculate the a0 and a1 coefficients for a desired centre frequency and -3dB
bandwidth.
w
NOTCH FILTER WORKED EXAMPLE
f
f
f
NFn_A0 = -a0 x 2
NFn_A1 = -a1 x 2
These values are then converted to a 14-bit sign / magnitude notation:
NFn_A0[13] = 1; NFn_A0[12:0] = 13’h1F95; NFn_A0 = 14’h3F95 = 14’b11111110010101
NFn_A1[13] = 0; NFn_A1[12:0] = 13’h1F85; NFn_A1 = 14’h1F85 = 14’b01111110000101
a
c
b
s
w
w
a
0
1
= 1000 Hz
= 48000 Hz
= 100 Hz
b
0
R
E
S
P
O
N
S
E
(dB)
=
=
=
=
−
1
1
-10
-15
-20
-25
-30
-35
-40
2
2
+0
-5
1 (
−
+
π
π
20
f
f
tan(
tan(
+
b
c
f /
f /
a
0
s
s
w
w
)
=
cos(
=
b
b
/
/
2
2
) 2
) 2
13
12
π
π
w
= -8085 (rounded to nearest whole number)
= 8069 (rounded to nearest whole number)
x (100 / 48000) = 0.01308996939 rads
x (1000 / 48000) = 0.1308996939 rads
=
0
50
)
1
1
=
−
+
tan(
tan(
−
1 ( +
. 0
. 0
. 0
100
0130899693
0130899693
9869949627
200
/ 9
/ 9
)
cos(
) 2
) 2
= 0.9869949627
. 0
1308996939
500
Frequency (Hz)
)
= -1.969995945
1k
2k
5k
10k
PD, Rev 4.2, April 2008
20k
Production Data
T T T
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