High-fidelity digital FM transmitter made by BH1417
The new generation of FM stereo transmitter IC: BH1417 series launched by Japan RHOM Company adopts a frequency synthesis circuit for its high-frequency oscillation part, and the oscillation frequency is stable. The audio signal processing integrates the pre-emphasis circuit, limiter circuit, and low-pass filter circuit (LPF), which greatly improves the quality of the audio signal compared with BA 1404.
The FM stereo transmitter board circuit made by BH1417 is shown in the figure.
Pin ①and pin {22} are audio signal input terminals. It is best to use ELNA audio-specific electrolysis or tantalum electrolysis for the coupling capacitor. Pin ③ and pin {20} are the adjustable ends of the low-pass filter. Connect a 150pF capacitor to filter out signals above 15kHz. Connect a 10μF electrolytic capacitor to the fourth pin to improve the reference voltage ripple coefficient. The stereo signal is output from the ⑤ foot, and the 10μF electrolytic capacitor also plays an important role in sound quality. Connect an adjustable resistor to adjust the sound level. Pin ⑦ is the PLL phase detection output. Peripheral capacitance, inductance, varactor diodes of the ⑨ foot constitute a voltage-controlled oscillation circuit. Pin {11} is the RF output terminal. Pins {15}-{18} are parallel data setting terminals, and the output frequencies corresponding to their high and low levels are shown in the attached table.
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