[Photo] Frequency-synthetic FM stereo transmitter IC-BH1417

2002, Issue 7, Category: Electronic Products and Devices

Many FM enthusiasts have used BA1400 to make FM stereo transmission circuits, but their transmission frequency is determined by the LC oscillator, which may cause oscillation frequency drift. In view of this, Japan ROHM has launched BH1414 ~ BH1417 FM stereo transmitter IC, the high-frequency oscillation part uses a frequency synthesis circuit, the oscillation frequency is very stable, and can easily change the transmission frequency. Among them, BH1414 and BH1415 are controlled by an external MCU. BH1416 and BH1417 can be changed by the parallel data setting end to transmit frequency. BH1416 is suitable for the Japanese frequency band, while BH1417 is suitable for the 88 ~ 108MHz frequency band in China.
BH1417 internally integrates a stereo modulation circuit, a phase-locked loop frequency synthesizer and a high-frequency oscillation circuit. The peripheral circuit of the FM stereo transmitter board composed of it is very simple. And it has pre-emphasis circuit, limiter circuit and low-pass filter, which can obviously improve the sound quality. The total harmonic distortion reaches 0.3%, the stereo separation is 40dB, and the RF output level is 100dBμV.
BH1417 adopts patch SOP22 package, the internal structure is shown in Figure 1. The functions of each pin are as follows:
The {1} and {22} pins are the left and right channel signal input terminals. The {2} and {21} pins are connected to the pre-emphasis circuit, and the time constant can be changed by the external circuit (T = 22.7kΩ × C). The {3} and {20} pins are the adjustable ends of the low-pass filter. An external 150pF capacitor can limit the input of signals above 15kHz. The {4} foot is the filter terminal, and an external capacitor can improve the ripple factor of the reference voltage. The {5} pin is the output of the stereo composite signal. The {6} pin is grounded, and the {7} pin is the output of the PL phase detector. The {8} foot is the power terminal, connected to + 5V power supply. {9} The foot is the end of the RF oscillator, which forms a voltage-controlled oscillation circuit with peripheral components. {10} The foot is the RF ground terminal. The {11} pin is the output terminal of the RF signal, and is connected to the antenna or the post-stage power amplifier through a band-pass filter. {12} The pin is the power supply terminal of PL. The {13} and {14} feet are connected to a 7.6MHz crystal oscillator. Pins {15} ～ {18} are parallel data setting terminals, and they control the output frequency of the transmitter. Pin {19} is the pilot signal adjusting terminal.
Figure 2 shows the typical application circuit of BH1417. The output frequency range is from 88.0MHz to 89.2MHz in 200kHz steps.

? Tianjin Yan Jing



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[Photo] Simple frequency modulation transmitting circuit with stable frequency

The working voltage of this circuit is 9V, working ...

Published on 2006-04-15 20:45 • 760 views
[Photo] Simple frequency modulation transmitting circuit with stable frequency
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