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 lowinductance 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 lowdistortion preamplifier and simultaneously applied to both signal, generated by a local voltagecontrolled oscillator (VCO), is counted down by two frequency dividers a 38kHz signal and to two 19kHz pilottone supplied by the FM detector is compared to the locally generated 19kHz signal in a synchronous detector. The resultant signal controls the voltage controlled oscillator (VC)) so that it produces an output signal to phaselock the stereo decoder with the pilot tone. A second sychronous detector compares the locally generated 19kHz signal with the 19kHz 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 38kHz synchronous detector, and automatically switches the NTE789 form monaural to stereo operation. The output signal from the 38kHz detector and the composite signal from the preamplifier are applied 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 16lead quadinline plastic package and operates over the ambient temperature range to +85°C. Features: D Requires the use of only one lowinductance tuning coil D Automatic stereo switching D Directly drives a stereo indicator lamp 100mA D Includes driver for stereolamp indicator D Operates from a wide range of power supplies: 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% D 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.
Absolute Maximum Ratings: (TA = +25°C unless otherwise specified) DC Supply Voltage. 16V Current Pin12. 100mA Input Signal Voltage (Composite)(Note 1). 400mV Operating Ambient Temperature Range. to +85°C Storage Ambient Temperature Range. to +150°C Lead Temperature (During Soldering, 1/32" (0.79mm) from case,10s max.). +265°C Note 1. For stereo operation, a minimum input signal voltage (composite) 40mV is required. Electrical Characteristics: (TA = 12 unless otherwise specified) Parameter Static Characteristics
Total Current Pin10,Pin11) DC Voltage Pin1 Pin6 (Indicator Lamp OFF) Pin9 and Pin10 Pin12 (Indicator Lamp OFF) Voltage Differential Pin1) Current at Pin12 (In actual use external circuit resistance (e.g. lamp should limit Pin12 to the maximum rated value of 100mA) Itotal V1 VIN (at = 16V Lamp OFF mA
Input Impedance Channel Separatiom + R Reference) Channel Balance (Monaural) Monaural Gain Stereo/Monaural Gain Ratio Indicator Lamp TurnON Voltage Capture Range (Deviation from 76kHz center frequency) Distortion (75µs Deemphasis) 2nd Harmonic 3rd, 4th, and 5th Harmonic 19kHz Rejection 38kHz Rejection SCA (Storecast) Rejection Stereo Defeat Voltage (V4) Stereo Enable Voltage (V4) Zin VIN = 180mV, Note 3 VIN = 180mV VIN = 180mV VIN = 180mV, Note 3 19kHz pilottone Pin1 19kHz pilottone voltage mV %
Note 2. For improved pilot sensitivity and overload characteristics, replace the.039µF capacitor between Pin7 and Pin8 with a Series LC Network = 0.015µF). Under these conditions, Indicator Lamp Sensitivity: "ON" = 3.3mV, "OFF" = 2.0mV. Note 3. For stereo operation, test conditions require a composite stereo input signal (modulated at 1kHz) including 19kHz (18mV) pilottone signal.
Composite FM 1 Detected Signal Input Bypass 2 GND 3 GND 4 GND 5 RC Network 6 19kHz Pilot Lamp 7 Sensitivity Network 8
Indicator Input 16 76kHz Network Capacitor Input 15 76kHz Network 14 Phase Lock Filter Loop Network 13 GND 12 Lamp Drive Circuit 11 VCC 10 Right Ch Output 9 Left Ch Output