U3550BM

U3550BM www.DataSheet4U.com Low-Power FM Transmitter / Synthesizer System 26 to 50 MHz Description The U3550BM is a radio-frequency IC for analog cordless telephone applications in the 26/50-MHz band (CTO standard). The IC performs full duplex communication. The transmitting and receiving frequency depends on whether the IC is used in the handset or in the base station. The U3550BM’s frequency converter consists of an FM transmitter with switchable output power and receiver Mixer 1 in the same unit. A two-wire bus interface can be used for frequency control as well as for switching the transmitter’s power amplifier and the receiver. Fine frequency adjustment of the reference crystal oscillator is programmable. The receive part is designed for a double-conversion architecture. The incoming radio-frequency signal will be filtered and amplified before reaching the first mixer. At this stage, the RF signal will be converted down to the first intermediate frequency (10.7 MHz) by using a local adjustable oscillator (VCO3). The frequency of this oscillator is controlled by the PLL. The transmitter part contains two PLL-controlled VCOs. The frequency modulation is accomplished by superposing the incoming audio signal on the first PLL control voltage. In this system, the frequency is a product of mixing VCO1 with local oscillator (VCO3). The FMmodulated carrier is amplified by external power amplifier before entering the output filter and the antenna connector. Features D All PLLs a...