BA1404 modulator circuit

BA1404 is a product of Toyo Corporation of Japan, with an operating voltage range of 1"3V. The circuit is a monolithic integrated circuit composed of an FM stereo mixer, 38KHZ oscillator, FM modulator and high-frequency amplifier. Working principle (see Figure 1): The stereo audio signal is input from pins 1 and 2 through the weighting and matching network, and then enters the FM stereo mixer after amplification to produce a stereo composite signal consisting of the L+R main signal and the LR secondary signal, which is buffered and amplified and output from pin 14. (Pins 16 and 17 can adjust the parameters of the composite signal and control the left and right balance); the external discrete components of pins 4, 5, and 6 and the internal circuit form a 38KHZ oscillator to generate a 38KHZ signal, which is buffered and amplified and supplied to the mixer and 1 respectively. /2 frequency divider, the 38KHZ signal gets a 19KHZ pilot signal through the divider and is output from pin 13; the composite signal and pilot signal are output from pins 13 and 14 and enter the FM modulator (9, 10) through the matching network through pin 11 The peripheral components of the pin determine the oscillation frequency) to generate an FM signal, which is amplified and output by pin 7; pin 2 is the AF bias, pin 3 is the AF ground point, pin 8 is the RF ground point, and pin 15 is the positive pole of the power supply. (Note: Pin 11 outputs a reference voltage to facilitate peripheral discrete components to control the oscillation frequency, which is not used here.) The signal at pin 7 is finally amplified and output by μpc1651. Production points: The circuit can be densely installed on a universal circuit board. Remove the excess copper points; the resistors on pins 13 and 14 are only reference values. Since their values ​​are related to the stereo separation, they should be set according to the actual situation; L is an iron-shell adjustable inductor, and its parameters are related to frequency. This is the key to frequency stabilization, so be careful; if you want to use mains power, pay attention to the power supply. Since the current is not large, you can use a discrete filtered voltage-stabilized power supply; the working voltage of μpc1651 is 5V, which must not be exceeded, as it is easy to burn out in the experiment. Summary: Since many netizens on the "Electronic News" BBS requested detailed information on FM stereo transmitters, I re-collected the relevant information and conducted experiments on simple discrete, combined, and integrated FM stereo transmitters. I felt that This combination of BA1404+μpc1651 is the easiest to make and debug, and the frequency stability is quite high (compared to the previous BA1404 circuit), and the transmit power will not exceed the legal range. Since I am still a student, my technical level is limited, and this experimental data is not available. This is a circuit design based on existing knowledge after collection. There must be many inadequacies. I hope anyone with common interests can give me some pointers. Parameter Unit Test Conditions Minimum Value Typical Value Maximum Quiescent Current IQ (mA) 3.5 3 5 Input Resistance Rin ( KΩ) f=1KHZ 360 540 720 Input gain GV(dB) Vin=0.5mv 30 37 Channel balance CB(dB) 2 Mixer output maximum voltage Vom(mvp-p) THD=<3% 200 38KHZ leakage voltage Voo( mv) When there is no signal 1 Pilot output voltage Vop (mvp-p) When there is no load 460 580 Channel separation Sep (dB) 25 45 Input noise Vin (μV) 1 High amplifier output maximum voltage Vosc (mV) 350 600