When the digital mobile phone is working, it uses the antenna to receive and transmit. In order to isolate the receiving channel from the transmitting channel and keep the unidirectional path, a component called duplexer is connected behind the antenna. The duplexer consists of a receiving filter, a transmitting filter and an antenna.

Closed circuit components? The signal received by the antenna enters the receiving circuit through the receiving filter of the duplexer. The signal output by the transmitting circuit is fed to the antenna for transmission through the transmitting filter of the duplexer.

2.PLL frequency synthesizer

Mobile communication devices usually use frequency synthesizers to provide a series of signal sources with high stability and accuracy. signal source

There are two main functions:? First, it is used to provide the RF signal of the transmitting circuit; ? The second is to receive the first local signal of the frequency conversion circuit.

Number.

Step 3: receiver

The receiver is actually a superheterodyne high frequency receiver with secondary frequency conversion. Its task is to choose from various wireless signals and interference waves.

Select the useful signal to receive. The wireless receiving part includes input loop high frequency filtering. High frequency amplification? Frequency conversion? IF filtering, IF amplification and demodulation. After receiving the high-frequency signal from the base station, the mobile phone sends it to a low-noise amplifier for high-frequency amplification. So as to improve the receiving sensitivity and the signal-to-noise ratio. The amplified high-frequency signal is sent to the first mixing circuit for down-conversion with the local oscillator signal provided by the phase-locked frequency synthesizer. The first intermediate frequency signal is gated by the frequency selection loop. The first intermediate frequency signal is mixed by a second mixer to obtain a second intermediate frequency. The signal is amplified and demodulated. Recover the digital signal. Digital signals include voice signals and various control information.

4. Transmitter

The function of the transmitter is to transmit the signal to be transmitted. (Voice signal,? Data signals, etc. )? Modulate on a radio frequency carrier. And amplified by strength.

Then it is transmitted to the base station in the form of radio waves through the antenna. The transmitter is mainly modulated by radio frequency. Radio frequency power amplification? Band-pass filtering and other parts.

The audio signal generated by the microphone is amplified at low frequency and sent to the voice circuit for modeling? Digital conversion speech coding? Channel coding? transmit

Knitting therapy? And then send it to the RF modulator. The modulated high-frequency signal is sent to the mixer and upconverted with the local oscillator signal provided by the phase-locked frequency synthesizer. The frequency doubling circuit improves the frequency of the mixed signal. Finally, it is amplified by a high-frequency power amplifier and fed in.

Transmitting antenna.

5. Microprocessor control unit

Microprocessor control unit is the main control part of mobile phone working state and each module state. Its core components are single chip microcomputer, memory and data processor. Used to complete the processing of complex signaling and system control. The mobile phone receives the signaling from the base station. Logic electricity

After processing, the channel coding instruction is issued to control the oscillation of the frequency synthesizer. So as to tune to the required operating frequency. Additional miniature

The processor is controlled by the stored program of the mobile phone. Can automatically search and select communication channels. Realize the switching control of the transceiver channel and send a busy tone to the user. Call tones and other signal tones. The control information generated by keyboard operation of this machine is sent to the microprocessor for processing.

Microprocessor control of mobile phone working state? Including timing control,? Digital system control? Transceiver control and man-machine

Interface control, etc.

The interface part is mainly as follows:

Voice interface? Such as transmitters and receivers? And then what? Switch interface.

Data interface? : mainly data terminal adapters.

Man-machine interface? : including pressing the keyboard, Interface between display and subscriber identification card.