TBA120 Demodulator Circuit

Description: The TBA120 Series integrated circuits (ICs) offer a high-gain limiting intermediate frequency (IF) amplifier and a quadrature coincidence detector in a single package. These ICs are primarily designed for the extraction of television intercarrier sound, which is frequency modulated onto a 5.5 MHz or 6 MHz subcarrier in Europe. The television waveform presents a significant interfering signal, and the TBA120 exhibits superior performance compared to earlier Foster-Seeley and Ratio Detector systems, significantly reducing the component count. The TBA120 functions as an amplitude modulation (AM) demodulator. Equivalent components include SN76660N (Texas Instruments) and S041P (the latter being a low-power variant). The TBA120 operates as a continuous wave (CW), single sideband (SSB), and AM multimode detector, with the beat frequency oscillator (BFO) line connected to the signal from the IF stage. It has been tested in the Drake 2-B receiver. It is important to note that variants such as TBA120AS, TBA120S, TBA120C, and TBA120D may not perform satisfactorily in this application. The device can also be adapted for use as an SSB detector; however, it is an older component, and its circuit is primarily of interest as a reference, with the maximum expected IF level being 50 mV RMS. The MC1351 should not exceed levels of 10-20 mV, while the TDA1576 may become overloaded with input levels above 100 mV RMS. Other components like NE/SA604/614 could potentially be utilized, although they have not been tested. The TBA120U serves as an IF amplifier with a symmetrical frequency modulation (FM) demodulator and an audio frequency (AF) amplifier that features adjustable output voltage. This AF amplifier includes an output for volume control and an input for VCR operation.

The TBA120 Series ICs are designed for applications requiring efficient extraction of intercarrier sound in television systems. The high-gain limiting IF amplifier is crucial for maintaining signal integrity while minimizing noise, which is essential in environments with significant electromagnetic interference. The quadrature coincidence detector allows for precise demodulation of the amplitude-modulated signals, enhancing the clarity of the audio output.

In practical applications, the TBA120 can be integrated into various television receiver designs, where its reduced component count leads to lower manufacturing costs and improved reliability. The versatility of the TBA120 as a multimode detector makes it suitable for a range of communication systems beyond television, including amateur radio setups where CW and SSB signals are prevalent.

The performance specifications indicate that the TBA120 operates optimally within specified voltage levels, making it essential to adhere to these parameters to avoid distortion or damage. The inclusion of a volume control output in the TBA120U variant allows for seamless integration into user interfaces, providing flexibility in audio management.

Overall, the TBA120 Series ICs represent a significant advancement in the field of audio signal processing, combining multiple functionalities into a single package while maintaining high performance and low power consumption.The TBA120 Series ICs provide a high-gain limiting IF amplifier and a quadrature coincidence detector in one package. These ICs are primarily intended for extraction of TV intercarrier sound, which (in Europe) is frequency modulated onto a 5.

5MHz or 6MHz subcarrier. The TV waveform constitutes an extreme interfering signal, and the TBA120 provides superior performance in comparison to early Foster-Seeley and Ratio Detector systems, with a considerable reduction in component count. TBA120 as AM demodulator. Equivalents are SN76660N (TI) and S041P (the latter is a low power version). It is in fact a CW/SSB/AM-multimode-detector, but the BFO line is connected to the signal from the IF.

Believe I tested it in my Drake 2-B. Please note that TBA120AS, TBA120S, TBA120C, TBA120D etc are different and may not function satisfactorily in this construction. It is also suggested the change for use as SSB detector, but it is an old device and the circuit has more interest as a reference IF level is supposed to be maximum 50mV RMS.

MC1351 should not have more than 10-20mV, and TDA1576 is overloaded with higher levels than 100mV RMS. NE/SA604/614 could also well be used, but have not been tested. The TBA120U is an i. f. amplifier with a symmetrical FM demodulator and an a. f. amplifier with adjustable output voltage. The a. f. amplifier is also provided with an output for volume control and an input for VCR operation.