BA1404 FM transmitter chip internal principle block diagram and application circuit diagram

BA1404 FM transmitter chip internal principle block diagram and application circuit diagram

BA1404 is a dedicated integrated circuit for stereo FM transmitter, which can also be used in remote control circuits. BA1404 is a product of the American ROHM company. It has high integration, requires few peripheral components, and works reliably. The power supply voltage has a wide adaptability range and can still work normally when it is as low as 1.5V.

Figure 1 BA1404 internal circuit principle block diagram

Figure 2 BA1404 application circuit

BA1404 application notes:

(1) In order to make the frequency characteristics of FM transmission consistent with the frequency characteristics of FM broadcast receiver, a pre-emphasis circuit with a time constant of 50μs needs to be connected in series to the left and right channel input terminals, 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.

(6) It is not easy to find a 38KHz crystal oscillator. A 57P capacitor can be connected between pins 5 and 6 of the circuit to work instead, but the three-dimensional effect will be less obvious.