NTE789
Integrated Circuit
Stereo Multiplex Decoder
Description:
The NTE789, a monolithic silicon integrated circuit, is a stereo multiplex decoder intended for FM multiplex
systems.
This stereo multiplex decoder requires only one low鈥搃nductance tuning coil (requires only one adjustment for
complete alignment), provides automatic stereo switching, energizes a stereo indicator lamp, and operates
from a wide range of voltage supplies.
Figure 1 shows the block diagram for the NTE789. The input signal form the detector is amplified by a low鈥揹is-
tortion preamplifier and simultaneously applied to both signal, generated by a local voltage鈥揷ontrolled oscilla-
tor (VCO), is counted down by two frequency dividers to a 38kHz signal and to two 19鈥搆Hz pilot鈥搕one supplied
by the FM detector is compared to the locally generated 19鈥搆Hz signal in a synchronous detector.
The resultant signal controls the voltage controlled oscillator (VC)) so that it produces an output signal to
phase鈥搇ock the stereo decoder with the pilot tone. A second sychronous detector compares the locally gener-
ated 19鈥搆Hz signal with the 19鈥搆Hz pilot tone. If the pilot tone exceeds and externally adjustable threshold
voltage, a Schmitt trigger circuit is energized. The signal from the Schmitt trigger lights the stereo indicator,
enables the 38鈥搆Hz synchronous detector, and automatically switches the NTE789 form monaural to stereo
operation. The output signal from the 38鈥搆Hz detector and the composite signal from the preamplifier are ap-
plied to a matrixing circuit from which emerge the resultant left and right channel audio signals. These signals
are applied to their respective left and right post amplifiers for amplification to a level sufficient to drive most
audio amplifiers.
The NTE789 utilizes the 16鈥搇ead quad鈥搃n鈥搇ine plastic package and operates over the ambient temperature
range of 鈥?0擄C to +85擄C.
Features:
D
Requires the use of only one low鈥搃nductance tuning coil
D
Automatic stereo switching
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Directly drives a stereo indicator lamp up to 100mA
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Includes driver for stereo鈥搇amp indicator
D
Operates from a wide range of power supplies: 10 to 16 volts
D
Requires only one adjustment for alignment
D
Switching from monaural to stereo and stereo to monaural produces no audible thumps
D
Low distortion: under 0.5%
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Separate dc input permits stereo defeat or enable
D
High signal output: directly drives audio amplifiers
D
Excellent SCA (storecast) rejection: 55dB typ.
D
High audio channel separation: 40dB typ.
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