Datasheet
f
c(HPF)
+
1
2p 10 kW C
I
C
I
+
1
2p 10 kW f
c(HPF)
C
I
+
1
2p R
I
f
c
f
c(LPF)
+
1
2p R
a
C
a
C
a
+
1
2p 1kΩ f
c(LPF)
f
c(LPF)
+
1
2p R
F
C
F
where R
F
is the internal 40 kW resistor
f
c(LPF)
+
1
2p 40 kW C
F
C
F
+
1
2p 40 kW f
c(LPF)
9 dB
f
c(HPF)
= 100 Hz
12 dB
AV
+20 dB/dec
−40 dB/dec
−20 dB/dec
f
f
c(LPF)
= 10 kHz
f
c(HPF)
+
1
2p R
I
C
I
where R
I
is the input resistor
TPA6211A1
SLOS367D –AUGUST 2003– REVISED JUNE 2011
www.ti.com
directly affects the bass (low frequency) performance
of the circuit. Consider the example where R
I
is 10
(8)
kΩ and the specification calls for a flat bass response
down to 100 Hz. Equation 2 is reconfigured as Therefore,
Equation 3.
(9)
(3)
Substituting 100 Hz for f
c(HPF)
and solving for C
I
:
In this example, C
I
is 0.16 μF, so the likely choice
C
I
= 0.16 μF
ranges from 0.22 μF to 0.47 μF. Ceramic capacitors
are preferred because they are the best choice in
At this point, a first-order band-pass filter has been
preventing leakage current. When polarized
created with the low-frequency cutoff set to 100 Hz
capacitors are used, the positive side of the capacitor
and the high-frequency cutoff set to 10 kHz.
faces the amplifier input in most applications. The
The process can be taken a step further by creating a
input dc level is held at V
DD
/2, typically higher than
second-order high-pass filter. This is accomplished by
the source dc level. It is important to confirm the
placing a resistor (R
a
) and capacitor (C
a
) in the input
capacitor polarity in the application.
path. It is important to note that R
a
must be at least
10 times smaller than R
I
; otherwise its value has a
Band-Pass Filter (R
a
, C
a
, and C
a
)
noticeable effect on the gain, as R
a
and R
I
are in
It may be desirable to have signal filtering beyond the
series.
one-pole high-pass filter formed by the combination of
C
I
and R
I
. A low-pass filter may be added by placing
Step 3: Additional Low-Pass Filter
a capacitor (C
F
) between the inputs and outputs,
R
a
must be at least 10x smaller than R
I
,
forming a band-pass filter.
Set R
a
= 1 kΩ
An example of when this technique might be used
would be in an application where the desirable
(10)
pass-band range is between 100 Hz and 10 kHz, with
a gain of 4 V/V. The following equations illustrate how
Therefore,
the proper values of C
F
and C
I
can be determined.
Step 1: Low-Pass Filter
(11)
Substituting 10 kHz for f
c(LPF)
and solving for C
a
:
C
a
= 160 pF
(4)
Figure 32 is a bode plot for the band-pass filter in the
previous example. Figure 31 shows how to configure
the TPA6211A1 as a band-pass filter.
(5)
Therefore,
(6)
Substituting 10 kHz for f
c(LPF)
and solving for C
F
:
C
F
= 398 pF
Step 2: High-Pass Filter
Figure 32. Bode Plot
(7)
Decoupling Capacitor (C
S
)
Since the application in this case requires a gain of
The TPA6211A1 is a high-performance CMOS audio
4 V/V, R
I
must be set to 10 kΩ.
amplifier that requires adequate power supply
Substituting R
I
into equation 6.
decoupling to ensure the output total harmonic
distortion (THD) is as low as possible. Power-supply
decoupling also prevents oscillations for long lead
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