Circuit Operating Descriptions
7-36
(5) IF Block
A. SAW FILTER
It passes only needed band of the signal that is converted to IF frequency and decrease other band to minimize
the effect of adjacent channel.
B. IF AMP
IF signal ,which is selected in SAW FILTER, is amplified in IF amp frequency enough to be detected. The IF AMP
has parallel inputs & outputs structure and consists of 3 series step AMP.Each step has about 20dB gains.These
gains are controlled by AGC voltage has maximum 63dB attenuation range.
C. RF AGC CONTROL
It is adjusted to determine RF AGC working point in tuner.
D. FM DETECTOR
After removing AM signal in the limiter AMP ,amplified SIF signal is applied FM detector.
This FM detector is PLL detecting type.
E. AFT DETECTER
AFT automatically controls the OSC frequency in the tuner, so that it retains a constant level.
It is a quadrature detection type. The carrier, which is detected from video det is directly input to AFT detector .
The 90 degree delayed phase signal is input at the same time to AFT detector and ,the results come out.
Detected AFT voltage is amplified by DC AMP and then applied to pin 13.
AUDIO
OUT
FROM TUNER
SECTION
SAW
FILTER
FM
DET
RF
AGC
IF
AGC
VIF
AMP
VIDEO
DET
AGC
1'
ST
AMP
1'
ST
DET
AFT
VCO
HPF
HPF
MIX
HPF
4.5MHz
BPF
VIDEO
OUT
SIF
TRAP
VCO TANK
VCC
EQ
AMP
AMP
TO TUNER
RF AGC
AFT OUT
Fig. 7-33 IF Ssection Block Diagram
Содержание SV-DVD40
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