WM8940
Pre-Production
1− tan(wb / 2)
1+ tan(wb / 2)
a0 =
a1 = −(1+ a0 )cos(w0 )
Where:
w0 = 2πfc / fs
wb = 2πfb / fs
fc = centre frequency in Hz, fb = -3dB bandwidth in Hz, fs = sample frequency in Hz
The actual register values can be determined from the coefficients as follows:
NFn_A0 = -a0 x 213
NFn_A1 = -a1 x 212
To configure Notch Filter 3 as a 1st order low pass filter, set the NF3_LP bit to 1 and calculate the
coefficients as follows:
a0 = 0
tan(wc / 2) −1
tan(wc / 2) +1
a1 =
Where:
wc = 2πfc / fs
fc = cutoff frequency in Hz, fs = sample frequency in Hz
The actual register values can be determined from the coefficients as follows:
NF3_A0 = 0
NF3_A1 = -a1 x212
DIGITAL ADC VOLUME CONTROL
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
REGISTER
ADDRESS
BIT
7:0
LABEL
DEFAULT
DESCRIPTION
R15
ADCVOL
[7:0]
11111111
( 0dB )
ADC Digital Volume Control
0000 0000 = Digital Mute
0000 0001 = -127dB
0000 0010 = -126.5dB
... 0.5dB steps up to
1111 1111 = 0dB
ADC Digital
Volume
Table 19 ADC Volume
Pre-Production, Rev 3.0, February 2007
26
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