WM8940GEFL 查看數據表（PDF） - Wolfson Microelectronics plc

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产品描述 (功能)

生产厂家

WM8940GEFL

Mono CODEC with Speaker Driver

Wolfson Microelectronics plc 

WM8940

Pre-Production

+0

-5

R -10

E

S

P

-15

O

N

S

-20

E

-25

(dB)

-30

-35

-40

20

50

100

200

500

1k

2k

Frequency (Hz)

T

5k

10k

20k

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

NOTCH FILTER WORKED EXAMPLE

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

w0 = 2πfc / fs = 2π x (1000 / 48000) = 0.1308996939 rads

wb = 2πfb / fs = 2π x (100 / 48000) = 0.01308996939 rads

a0

=

1− tan( wb

1+ tan(wb

/ 2)

/ 2)

=

1− tan(0.01308996939 / 2) = 0.9869949627

1+ tan(0.01308996939 / 2)

a1 = −(1+ a0 )cos(w0 ) = −(1+ 0.9869949627)cos(0.1308996939) = -1.969995945

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 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

w

Pre-Production, Rev 3.0, February 2007

82

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