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 the FM tuner IF stage. The IF amplifier and limiter stage consist of 6 stages of a double-ended differential amplifier having an excellent AMR, and this stage is followed by the signal meter driver which consists of 4 stages of the 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 preamplifier 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 the amplitude component at the time of the 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 bandwidth by means of an external resistor, and the built-in tuning meter null (short) circuit forces the tuning meter to be [0] when the IF amplifier stops working. The IF amplifier stop circuit, being a circuit to stop the FM IF amplifier at the time of AM reception, makes it possible to decrease shock noise due to FM-AM receiving mode switchover.
