Tfa9812, Nxp semiconductors – NXP Semiconductors TFA9812 User Manual
Page 17
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
. 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
.
The transfer function of this all-pass filter is shown in
:
(2)
A(z) is the second-order filter structure. The transfer function of A(z) is shown in
:
(3)
The relationship between the programmable parameters K
0
, K
1
, and K
2
and the filter
parameters G,
ω
, Q is shown in
Use
to calculate band suppression (G < 1) functions.
(4)
Use
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
<