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C-1408T
C-1408T
e SIF, S-Detector and DC-Attenuator Circuits
A single chip IC, in Fig. 16, provides the PIF, P-detector,
AFT, SIF, S-detector and DC-attenuator circuits. The
Audio freq.: 400 Hz
audio IF signal from the PIF amplifier of IC201 is trans-
1
Modulation: pes a
ferred to the SIF detector circuit via the preamplifier to
Sound
control:
Max.
provide the SIF (5.5 MHz) signal, which yet contains
i
video signals, at pin
@Q . The output signal is then
eeu
[pe
filtered at the band-pass filter (CF301) to eliminate
4
the video signals. The pure 5.5 MHz signal is fed into pin
| ov
a
3m,
() 2
Figure 14.
In IC201, the SIF signal is detected at the FM detector
(peak differential
detector) circuit through the limiter
Output Characteristic of DC Attenuator Circuit
amplifier to provide the audio signal. Then, the audio
Atpin (2 ( ) )
signal is sent to the DC attenuator circuit, where its
signal amplitude is regulated with the DC voltage of
pin (@2 , and the resultant signal appears at pin (7 via
the audio driver amplifier.
Here, C312 at pin @) is a capacitor of the deemphasis
circuit, and resistor at pin
(@ determines the gain of
amplifiers with different feedbacks of the audio driver
amplifier.
See Fig. 14 for the audio output signals and Fig. 15 for
the signal processing at the DC attenuator circuit.
DC Voltage (V) at pin
=
The sound control varies__..
in this range.
Audio Output Signals at pin ()) ( (0 )
'
(SA)
L301
TO IC 801
$P301
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I1c305
C233;
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Q203,
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R304
L202
00
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+
Mcs08
czo7f
(6)
Ic301
Qae@oa
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R213,
:
0) Py
i
R303
(d-da)
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uid
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c31077
e@ Audio Output Circuit
Figure 15.
The audio signal coming from IC201 is applied to IC301
via pin @) where it is amplified by about 30 dB and goes
out of pin G) of 1C301.
Capacitor at pin @) is to prevent abnormal noise which
may be caused when the power switch is turned on.
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R202
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11
12
Figure
16.
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