Toshiba RD-XS24SB Service Manual page 163

13-3 Tuner
1) 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.
2) Single tune
This consists of a filter circuit, RF AMF, impedance conversion circuit, image trap and a single tuning circuit. It
prevents noise and other interference signals. It is very important part which improves NF (noise figure) and
prevents the various of spurious signals.
3) RF AMF
RF AMF is made of FET (Field Effects Transistor). It is controlled by AGC coming from IF DEMOD block.
4) Double tune
It consists of a double tuning circuit to improve characteristic of rejection that results in a better band
characteristic.
5) Mixer IC (Mixer, OSC, PLL)
It consists a VHF and UHF OSC and Mixer circuit. We applied mixer to make better characteristic of rejection,
it shows especially various beat characteristic.
6) PLL IC
The PLL IC plays a role selection of Tuner channel. It was built-in three wire PLL IC, charge pump and band
driver.
The minimum of step frequency is 31.25KH z.
VHF
a
b
8.P.F
~
Fran
Modulafor
~
~
VHF
Single Tune
VHF VHF
d
VHF Double Tune
SingleTune
c
RF Amp
VHF Mixer
VHF
VHF
-RF Amp
Double Tune
e
3
1
IF Amp
Mixer
OSC 8uffer
VHF OSC
Mix IC IC100 7 8
VHF OCS
VHF
VHF OSC
Fig.13-3
IF Single
5
12
f PLL IC
4
9
1/8 Prescaler
OSC Amp
Prog.Dirlder
3
2
Phese Code
1
Charge Pump
L.P.F
16
^
&
PB TU
Circuit Operating Descriptions
Fram IF Sectlon
>
<
AGC
TO IF Sect lon
< >
IF
Fram IF Sect lon
< >
+B
V V U
L
H
10 9 8 6
Band Driver
4MHz
15 X-tal
Band Driver
~
1
3wice Bas
Recelver
14
13 12
) 1
* (
LOCK
CLOCK DATA ENABLE
13-3