WM8983_06 Datasheet, PDF (42/123 Pages) Wolfson Microelectronics plc – Mobile Multimedia CODEC with 1W Speaker Driver

WM8983
NOTCH FILTER WORKED EXAMPLE
Production Data
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 = 2πf _c / f _{s = 2π x (1000 / 48000) = 0.1308996939 rads}
w_b = 2πf _b / f _{s = 2π x (100 / 48000) = 0.01308996939 rads}
a₀
= ^{1 − tan(wb}
1 + tan(w_b
/ 2)
/ 2)
=
1 − tan(0.01308996939 / 2)
1 + tan(0.01308996939 / 2) _{= 0.9869949627}
a₁ = −(1 + a₀ ) cos(w₀ ) _{= − (1 + 0.9869949627) cos(0.1308996939) = -}
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
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:
0.5 × (G-255) dB for 1 ≤ G ≤ 255;
MUTE for G = 0
w
PD Rev 4.0 November 2006
42