Transmitter circuit composed of BA1404

Relevant key device information applied in this article: BA1404 BA1404 is a special integrated circuit for FM stereo emission. Due to its excellent working performance, it is also often used for radio remote control. BA1404 requires low operating power supply voltage, low power consumption, complete circuit structure, and required external connections. Few components, stable and reliable operation. When using BA1404, you should pay attention to the following matters: (1) In order to make the frequency characteristics of the transmitter consistent with the frequency characteristics of the FM broadcast receiver, it is necessary to connect the left and right channel input terminals in series for a period of time The pre-emphasis circuit with a constant of 50μs is as shown in the figure. When used in a radio remote control transmitting circuit, the left and right input terminals can be combined and connected to the signal input terminal with a 0.1~1μF capacitor. (2) External R and C components are connected to pins 12 to 14 to ensure that when the output signal of the stereo modulator and the pilot signal are combined into a composite signal, the phase characteristics of the two are consistent and the channel separation is not worsened. Under normal circumstances, no changes are allowed. . If any changes are needed, they should be determined after actual testing. (3) During stereo modulation, the upper limit of the audio frequency of the modulated signal is 19kHz. If the input signal is accompanied by a pulse signal, in order to prevent buzzing and deterioration of channel separation, a low-pass filter should be connected in series at the input end. (4) Pins 16 to 17 are used to adjust the balance. Even if these two pins are not connected to anything, satisfactory separation can be obtained. In normal use, a 50kΩ potentiometer is always connected to further improve the separation by adjusting the DC balance. (5) The DC output voltage of pin 11 is fixed to VDD~0.7V by the internal circuit.