Digital transmitter and receiver system using direct modulation and demodulation processes

摘要

The system has a reception part for selectively receiving and amplifying a desired channel band signal. The amplified signal is mixed with the carrier frequency and a modulated signal is subtracted. The signal is compared with a reference signal, and the demodulated signal is output. A transmitter provides power amplification of a demodulated transmission signal, filters the interference components, and outputs a filtered signal. A transmission and reception control switch connects the antenna to the transmitter or receiver, according to a mode signal. A PLL modulator generates the carrier frequency according to an oscillator control signal, and outputs the carrier frequency. The transmission data are modulated according to a frequency sample. The data is output. A second transmission selection switch switches an output of the PLL modulator to the transmitter or receiver, according to the transmission mode control signal. A control part identifies the frequency offset of the received demodulated data, or monitors the carrier frequency from the PLL modulator. An oscillator control signal is generated to keep the carrier frequency constant, and provide a transmission and reception mode signal according to an operating state.