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(4) Tuner Block
A. Low pass filter & high pass filter
This consists of IF trap circuit and UHF & VHF separation circuit. If the input signal is IF(45.75MHz), this filter
prevents interference.
B. Single tune & RF AMP
This consists of a filter circuit, RF AMP, impedance conversion circuit, image trap and a single tuning circuit. It
prevents noise and other interference signals. RF AMP is controlled by AGC come from IF DEMOD block.
C. Double tune
It consists of a double tuning circuit to improve rejection characteristic which results in a better band characteris-
tic.
D. MOP IC (Mixer, OSC, PLL)
It consists a VHS and UHF OSC and mixer circuit. We applied a double balance mixer to have better rejection
characteristic, it shows especially various beat characteristic.
It serects channels and contains charge pump band driver. The minimum step standard frequency 27.97KHZ.
L.P.F
FROM
MD SECTION
H.P.F
S.T(VL)
H.P.F
+
V.RF Amp
IF trap
S.T(VL)
S.T(U)
U.RF Amp
AGC
from IF Section
Fig. 7-32 Tuner Section Block Diagram
D.T(VL)
D.T(VH)
VHF
OSD
D.T(U)
UHF
OSD
LPF
Tu voltage
out
Circuit Operating Descriptions
MOP IC
CXA3250AN (SONY)
SN761672A (TEXAS Instruments)
V.MIX
U.MIX
IF
OSC
AMP
AMP
Prescaler
C.P.
BAND SW
REF
Fsc IN
Tu
Clock
Data
+B
IF
S.T
IF
to IF Section
VL
VH
U
7-35
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