LA1235 FM IF System Applications
Overview
The LA1235 is a high integrated IC developed for use in
high S/N, low distortion FM IF system applications. This
IC features S/N=88dB, distortion factor=0.015% and has
almost all functions required for FM tuner IF stage.
The IF amplifier and limiter stage consist of 6 stages of
double ended differential amplifier having an excellent
AMR, and this stage is followd by the signal meter driver
which consists of 4 stages of level detector, thereby
creating extended linearity up to strong input. The FM
detector stage consists of a double balanced quadrature
detector to which a low frequency preamplifire and a
muting controller are attached. The muting drive stage
consists of an OR circuit for weak signal muting drive
output which detects signal intensity and detuning muting
drive output which detects S curve DC output and enables
the prevention of noise at the time of weak signal and
detuning. Further, the weak signal muting drive output
circuit contains a Schmitt circuit having hysteresis and
enables the prevention of muting malfunction due to
amplitude component at the time of weak signal. The AFC
output and tuning meter drive stage is of current drive type
which makes it possible to adjust AFC sensitivity and
muting band width by means of an external resistor, and
the built-in tuning meter null (short) circuit foreces the
tuning meter to be [0] when th IF amplifier stops working.
The IF amplifier stop circuit, being a circuit to stop the FM
IF amlifier at the time of AM reception, makes it possible
to decrease shock noise due to FM-AM receiving mode
switchover.
Functions
&127; IF amplifier, Limiter.
&127; Quadrature detection.
&127; AF preamplifier.
&127; Signal intesity muting drive output.
&127; Detuning muting drive output.
&127; AF signal muting circuit.
&127; Signal meter drive output.
&127; AFC, tuning meter drive output.
&127; IF amplifier stop circuit.
&127; Tunig meter null circuit.
Features
&127; High S/N (88dB typ.).
&127; Low distortion (0.015% typ.).
&127; Weak signal muting dirve output having hysteresis.
&127; Tuning mete null (short) circuit.
&127; Signal meter dirve output having wide dynamic range.
&127; High limiting sensitivity.
&127; Built-in constant-voltage regulated circuit (Operating
voltage : 10 to 14V).
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