NXP Semiconductors TFA9812 - Manual (Page 18)

TFA9812_2 © NXP B.V. 2009. All rights reserved.
Preliminary data sheet Rev. 02 — 22 January 2009 18 of 66
NXP Semiconductors
TFA9812
BTL stereo Class-D audio amplifier with I 2 S input
(5)
The ranges of the TFA9812 parametric equalizer settings for each band are:
• The Gain, G is from
−
30 dB to +12 dB.
• The center frequency, f
c
is from 0.0004 * f
s
to 0.49 * f
s
.
• The quality factor Q is from 0.001 to 8.
Using I 2 C control, filter coefficients need to be entered for each filter stage to configure it
as desired.
Figure 6 , Figure 7 and Figure 8 show some of the possible transfer functions of the
equalizer bands. The relations are symmetrical for the suppression and amplification
functions. A skewing effect can be observed for the higher frequencies.
Different configurations are available for the same filter transfer function, thus allowing
optimum numerical noise performance. The binary filter configuration parameters t
1
and t
2
control the actual configuration and should be chosen according to Equation 6 .
(6)
A maximum of 12 dB amplification per equalizer stage can be achieved with respect to the
input signal. Each band of the equalizer is provided with a
−
6 dB amplification, so in order
to prevent numerical clipping for some filter settings with over 6 dB of amplification, band
filters can be scaled by 0 dB or
−
6 dB. For optimum numerical noise performance steps of
−
6 dB amplification should be applied to the highest possible sections that are still within
scale signal processing safeguards. Band filters can be scaled with the binary parameters
listed in
Table 14 .
8.5.1.3 Equalizer band control
For compact representation with positive signed parameters, parameters k
1
’ and k
2
’ are
introduced in Equation 7 .
The parameters k
0
, k
1
', k
2
', t
1
, t
2
and s must be combined in two 16-bit control words,
word1 and word2, and must fit within the representation given in Table 15 . Parameters k
1
'
and k
2
' are unsigned floating-point representations in Equation 8 .
Table 14. Equalizer scale factor coding
s scale factor (dB)
0 0
1
−
6
K
0
G =
K
1
ω
cos – =
K
2
2Q
ω
sin –
( )
2Q
ω
sin +
( ) ⁄
=
G 1
≥
t
1
0
ω
<=
π
2
⁄
1
ω
>
π
2
⁄


=
t
2
0 k
2
>=0
1 k
2
<0



=