NXP Semiconductors TFA9812, Предварительный информационный лист

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TFA9812_2 © NXP B.V. 2009. All rights reserved.
Preliminary data sheet Rev. 02 — 22 January 2009 17 of 66
NXP Semiconductors
TFA9812
BTL stereo Class-D audio amplifier with I
2
S input
In the above equation f
c
is the center frequency and f
s
is the sample frequency.
The definition of the quality factor is the center frequency divided by the 3 dB bandwidth,
see
Equation 1 . In parametric equalizers this is only valid when the gain is set very small
(
−
30 dB).
(1)
Each band filter can be programmed to perform a band-suppression (G < 1) or a
band-amplification (G > 1) function around the center frequency.
Each band of the TFA9812 equalizer has a second-order Regalia-Mitra all-pass filter
structure. The structure is shown in
Figure 5 .
The transfer function of this all-pass filter is shown in Equation 2 :
(2)
A(z) is the second-order filter structure. The transfer function of A(z) is shown in
Equation 3 :
(3)
The relationship between the programmable parameters K
0
, K
1
, and K
2
and the filter
parameters G,
ω
, Q is shown in Equation 4 and Equation 5 .
Use Equation 4 to calculate band suppression (G < 1) functions.
(4)
Use Equation 5 to calculate band amplification (G
≥
1) functions.
Fig 5. Regalia filter flow-diagram
Q
f
c
f
2
f
1
–
----------------- ; =
f
1
: 20
10
A
f
1
A
f
c
--------
 
 
 
log 3dB f
c
f
1
>
=
f
2
: 20
10
A
f
2
A
f
c
--------
 
 
 
log 3dB f
2
f
c
>
, =
½
X(z)
A(z)
s
Y(z)
+
+
+
−
010aaa406
K
0
/2
H z
( )
1 2
⁄
1 A z
( )
+
( )
K
0
2
⁄
1 A z
( )
–
( ) ⋅
+
⋅
=
A z
( )
K
1
K
2
1 K
1
+
( )
Z
1 –
Z
2 –
+
⋅ ⋅
+
1 K
2
1 K
1
+
( )
Z
1 –
K
1
Z
2 –
⋅
+
⋅ ⋅
+
---------------------------------------------------------------------------------
=
K
0
G =
K
1
ω
cos – =
K
2
2Q G
ω
sin –
⋅ ( )
2Q G
ω
sin +
⋅ ( ) ⁄
=
G 1
<