92706 / 12506 MS OT B8-6236 No.A0203-1/5
LA1235M
Overview
The LA1235M is an FM IF system IC developed to feature a high signal-to-noise ratio and low distortion. It features a
signal-to-noise ratio of 88dB and a distortion of 0.015%, and is a highly integrated IC that provides essentially all the
functions related to the IF stage of an FM tuner. The IF amplifier and limiter stage consists of an AMR 6-stage
double-ended differential amplifier and the signal meter drive circuit that runs in parallel with that circuit consists of a
4-stage level detection circuit that features a wide linearity range through powerful input levels. The FM detection
circuit is a double balanced quadrature detection circuit that includes the associated low-frequency preamplifier and
muting control circuits. The muting drive stage consists of a circuit that takes the logical OR of the weak signal muting
drive circuit that detects the signal strength and the detuning muting drive circuit that detects the S-curve DC output,
and thus can also prevent noise associated with the tuner being in the detuned state. Additionally, the weak signal
muting drive circuit includes a Schmitt circuit, which has hysteresis to prevent incorrect muting operation due to
amplitude components in the weak signal. The AFC output and tuning meter drive stage are current drive type circuits
and allow the AFC sensitivity and detuned state muting band to be adjusted. Furthermore, this stage includes a tuning
meter null (short) circuit so that, when the IF amplifier is stopped, the tuning meter can be forcibly set to 0. The IF
amplifier stop circuit stops the FM IF amplifier during AM reception and minimizes impulse noise due to switching
between the FM and AM reception modes.
Functions
IF amplifier and limiter.
Quadrature detection.
AF preamplifier.
Signal strength muting drive output.
Detuning muting drive output.
AF signal muting circuit.
Signal meter drive circuit.
AFC and tuning meter drive output.
IF amplifier stop circuit.
Tuning meter null circuit.
Ordering number : ENA0203
Monolithic Linear IC
FM IF System IC
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at values that exceed, even momentarily, rated values (such as maximum ratings, operating condition
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products described or contained herein.