Sansui 6060 - Page 19

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FM IF SYSTEM BLOCK DIAGRAM
(IC HA1137W)
10.7MHz Coil
2000) 703
Audio Out
(to MPX IC)
Mute
Mute Circuit Circuit
SIGNAL METER
* Functions (IC HA1137W)
This IC has operating functions of various circuits as
listed below.
1) IF AMP.
2) Quadrature detection.
3) Low-Noise audio Preamp.
4) Delayed AGC detector and driver for Front-end.
5) Signal meter circuit.
6) Center meter circuit.
7) Muting (operation to input signal strength).
8) Muting (operation at detuning).
9) Multipass circuit? -~- --
* Main features (IC HA1137W)
1. This IC includes all functions required in FM iF stage.
2. As indicated above, this IC has functions of Muting
circuit which operates below a certain input signal
level. And also the IC includes new muting circuit,
namely it has 0 volt switch which operates the mu-
. ting circuit when the difference (absolute value) of
detector output voltage between Tuning-ON and
Detuning exceeds a certain voltage, utilizing S-curve
characteristics of FM detector. By this advantage, it
is possible to eliminate or avoid “Pop noise” caused
by variation of the DC voltage at tuning-OFF.
3. The IC makes it possible to produce high-quality
tuner having better selectivity and sensitivity by
connecting 6-element filters between Front-end and
the IC, as it has higher gain and better suppression
ratio in amplitude modulation.
4. Linear swing of signal meter is obtained.
> Main features of PLL (IC HA1196)
In the multiplex demodulation circuit, because of sub-
carrier wave (38kHz) being required for demodulation,
the pilot signal (19kHz) sent from FM stereo broadcast-
ing station is being made while doubling.
It is necessary for this sub-carrier wave that its phase
confirms to that of pilot signal correctly, and if there is
any phase difference between them, FM stereo separa-
tion becomes poor.
In the conventional products, LC resonance circuit has
been used so far for the circuit of this section, on the
other hand, in model 7070, IC in PLL is used, which
prevents FM stereo separation from becoming poor due
to deviation in resonance frequency or phase to tempa-
rature change and, in result, ensures stereo separation
of more than 50dB at 1kHz.
Advantages
1) Selectivity is superior.
2) Phase characteristics is good.
3) It is virtually not affected by temperature.
4) No secular change occurs.
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