STMicroelectronics Pop-free 120 mW stereo headphone amplifier DEMOTS488S DEMOTS488S データシート
製品コード
DEMOTS488S
Application information
TS488-TS489
24/32
Doc ID 11971 Rev 5
Note:
In case F
CL
is kept the same for calculation, It must be taken in account that the
1st order high-pass filter on the input and the 1st order high-pass filter on the
output create a 2nd order high-pass filter in the audio signal path with an
attenuation 6 dB on F
output create a 2nd order high-pass filter in the audio signal path with an
attenuation 6 dB on F
CL
and a roll-off 40db
⁄
decade.
4.4
Higher cutoff frequency
In the high-frequency region, you can limit the bandwidth by adding a capacitor C
feed
in
parallel with R
feed
. It forms a low-pass filter with a -3 dB cutoff frequency F
CH
. Assuming that
F
CH
is highest frequency to be amplified (with a 3 dB attenuation), the maximum value of
C
feed
is:
Figure 79.
Lower cutoff frequency vs.
input capacitor
input capacitor
Figure 80.
Lower cutoff frequency vs.
output capacitor
output capacitor
1
10
100
1000
10
100
1k
10k
Rin=50k
Ω
Rin=100k
Ω
Rin=20k
Ω
Lo
w
er C
u
t-
o
ff fr
eq
uency (Hz
)
Cin (nF)
Rin=10k
Ω
0.1
1
10
100
1000
10
100
1k
10k
R
L
=32
Ω
R
L
=600
Ω
R
L
=16
Ω
Lo
wer
C
u
t-off fr
e
que
nc
y
(Hz
)
Cout (
μF)
Figure 81.
Higher cutoff frequency vs. feedback capacitor
F
CH
1
2
π R
feed
C
feed
⋅
⋅
---------------------------------------------
=
0.01
0.1
1
10
100
100
1k
10k
100k
Rfeed=40k
Ω
Rfeed=80k
Ω
Rfeed=20k
Ω
H
igh
e
r C
u
t-off F
requen
c
y
(kH
z
)
Cfeed
(
μF
)
Rfeed=10k
Ω