ABSTRACT
In this paper, a FM transmitter is proposed. It is based on a dedicated chip BH1417F, with the necessary composition of the external circuit. The main circuit includes an audio signal processing circuit, a FM modulation circuit and a power amplifier. Audio signal can be inputted from a microphone or line input. Using a processing circuit, which includes a pre-emphasis circuit, a limiter, a low-pass filter and mixer, the audio signals are composed into stereo signal. The stereo signal is then modulated by the FM modulation circuit. A power amplifiers enlarge the modulated signal and transmit out with the antenna. The frequency band of the FM transmitter can be chosen between 87.7MHz-88.9MHz or 106.7MHz-107.9MHz. With the digital phase-locked loop integrated in the BH1417F, high frequency stability can be achieved. The total transition power is less than 20mW. Tests show that FM signal can be received within 10 meters, and the design objectives are basically realized.
