Circuit Block - Toshiba CN27E90 Technical Training Manual

1. CIRCUIT BLOCK

EL466L
Tuner
RF AGC
1-1. Outline
(1) RF signals sent from an antenna are converted into
intermediate frequency band signals (video: 45.75 MHz,
audio: 41.25 MHz) in the tuner. (Hereafter, these signals
are called IF signals.)
(2) The IF signals are band-limited in passing through a
SAW filter.
(3) The IF signals band-limited are detected in the VIF
circuit to develop video and AFT signals.
(4) The band-limited IF signals are detected in the SIF
circuit and the detected output is demodulated by the
audio multiplexer, developing R and L channel outputs.
These outputs are fed to the A/V switch circuit.
(5) A sound processor (S.PRO.) is provided.
1-2. Major Features
(1) The VIF/SIF circuit is fabricated into a small module by
using chip parts considerably.
(2) As the tuner, EL466L that which contains an integrated
PLL circuit is employed.
(3) Wide band double SAW filter F1802R used.
(4) FS (frequency synthesizer) type channel selection system
employed.
IF/MTS/S.PRO Module MVUS34S
VIF/SIF
SAW
Circuit
Filter
TP12
Video output
AFT output
Fig. 2-1 Block diagram
17
SIF
output
Sound
Multiplex
Circuit
C-IN
TV TV
R-OUT L-OUT
To A/V switch circuit
(5) VIF/SIF circuit uses PLL sync detection system to
improve performances shown below:
• Telop buzz in video over modulation
• DP, DG characteristics (video high-fidelity
reproduction)
• Cross color characteristic (coloring phenomenon at
color less high frequency signal objects)
(6) HIC SBX1637A-22 is used in the audio multiplexer
circuit to minimize the size with increased performance.
(7) As a sound control processor, TA1217N is used. I
bus data control the DAC inside the IC to perform
switching of the audio multiplexer modes.
S.PRO Circuit
R-IN L-IN
C-OUT
R-OUT
L-OUT
(L+R)
-OUT
2
C-