WM8985_07 WOLFSON [Wolfson Microelectronics plc], WM8985_07 Datasheet - Page 41

• Manufacturer Part Number: WM8985_07
• Description: Multimedia CODEC With Class D Headphone and Line Out
• Manufacturer: WOLFSON [Wolfson Microelectronics plc]

Pre-Production
w
NOTCH FILTER WORKED EXAMPLE
DIGITAL ADC VOLUME CONTROL
Table 18 ADC Digital Volume Control
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
NFA0 = -a0 x 2
NFA1 = -a1 x 2
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
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;
a
a
w
w
R15 (0Fh)
Left channel
ADC Digital
Volume
R16 (10h)
Right channel
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
13
12
/
/
2
2
) 2
) 2
= -8085 (rounded to nearest whole number)
= 8069 (rounded to nearest whole number)
π
π
w
7:0
8
7:0
8
BIT
x (100 / 48000) = 0.01308996939 rads
x (1000 / 48000) = 0.1308996939 rads
=
0
)
1
1
=
−
+
tan(
tan(
−
ADCLVOL
[7:0]
ADCVU
ADCRVOL
[7:0]
ADCVU
1 ( +
LABEL
. 0
. 0
. 0
0130899693
0130899693
9869949627
MUTE for G = 0
11111111
( 0dB )
Not
latched
11111111
( 0dB )
Not
latched
DEFAULT
/ 9
/ 9
)
cos(
) 2
) 2
= 0.9869949627
. 0
1308996939
Left ADC Digital Volume Control
0000 0000 = Digital Mute
0000 0001 = -127dB
0000 0010 = -126.5dB
... 0.5dB steps up to
1111 1111 = 0dB
ADC left and ADC right volume do not
update until a 1 is written to ADCVU (in
reg 15 or 16)
Right ADC Digital Volume Control
0000 0000 = Digital Mute
0000 0001 = -127dB
0000 0010 = -126.5dB
... 0.5dB steps up to
1111 1111 = 0dB
ADC left and ADC right volume do not
update until a 1 is written to ADCVU (in
reg 15 or 16)
)
= -1.969995945
DESCRIPTION
PP, Rev 3.5, January 2007
WM8985
41