Generally speaking, we ordinary users only need to learn how to use the mobile phone well, and we don't need to study its specific working principle carefully; However, in the process of using mobile phones, due to various factors, mobile phones will inevitably malfunction. If you encounter even the smallest fault every time, it may be troublesome to send it to a professional repair shop for repair. If you have good electrical knowledge, you may want to learn to repair it yourself, but if you want to learn to repair it, you must be familiar with the working principle of the mobile phone first. Only in this way can you judge the cause of the fault and find out the corresponding solution. At the same time, understanding the working principle of mobile phones can also be used as a knowledge reserve for ordinary people. In order to help these users who love mobile phones learn to repair quickly, the author takes Motorola mobile phones as an example to introduce how mobile phones work in detail. The reason why mobile phones can communicate with each other is because it is the result of the cooperative work of radio frequency part, logic part and power supply part. To understand the working principle of mobile phones, we only need to understand how these three parts work. The following author will introduce the working principles of these three parts respectively. The radio frequency part is usually a radio frequency part, which consists of a signal receiving part and a signal sending part. When a mobile phone receives a signal, it first separates the received RF signal of 935-960MHz from the received RF signal through U400 and SW363, so that the transceivers do not interfere with each other. Input the fourth pin of U400 and output the fifth pin, and enter the receiving front-end loop. The working state of U400 is controlled by the third pin potential, which in turn is controlled by TXON and RXON signals sent by CPU. The RF signal passing through the antenna switch is filtered by the band-pass filter FL45 1 and then sent to the high-frequency amplifier Q4 18 for amplification. The output of Q4 18 is filtered by FL452 and sent to Q420 mixer for mixing. The local oscillator signal is generated by RXVCO, filtered by FL453 and sent to the base of Q420 for mixing, and the difference is taken. The collector of Q420 outputs an intermediate frequency signal of 153MHz, and after filtering by FL420, a pure signal of 153MHz is obtained. Now it is amplified by Q42 1 and sent to 3 1 of U2065438. The intermediate frequency signal of 153MHz and the carrier signal of 153MHz are demodulated within 32D53 to generate RXI and RXQ analog baseband signals, which are sent to U50 1 14# and/kloc-through 46# and 48# of U20 1. After A/D conversion in U50 1, it is sent to digital signal processor for further processing. The carrier wave of 153MHz is a 306MHz oscillator circuit composed of 4 1#, 42# and 43# of U20 1, which forms a wave signal of 306MHz, and after two frequencies, forms the carrier wave of 153MHz. In the transmitting part, TXIN, TXIP, TXQN and TXQP signals output from 2 1#, 22#, 23# and 24# of 50 1 enter 6 1#, 62#, 63# and U20 1. U20 1 6#, 7# and 10# are externally connected with a VCO of 2 16MHz to generate a carrier signal of 2 16MHz, which is divided by the frequency divider in U20 1 to generate the transmission of 108MHz. Four modulated signals are modulated by 108MHz carrier in U20 1 and output from the 4 # pin of U300. U300 completes the phase smoothing frequency between the transmitted sampling signal and TXVCO, and takes the difference to obtain 108MHz signal and TXIF input of No.4 to generate phase discrimination error voltage, which is output from the eighth pin to control the capacity of varactor CR300 and change the oscillation frequency of TXVCO. The 890-9 15MHz transmission signal output from the C pole of Q300 enters the power amplifier Q302 after being amplified by Q30 1 and pushed by Q302. The amplified signal enters the 1 pin of the antenna U400, and then is emitted from the 4# transmitting antenna of U400. The logic part is in the logic part. After the D/A conversion, decryption and adaptive equalization of the received RXI and RXQ analog baseband signals are completed in the modem U50 1, the digital baseband signals are sent from 6# of U50 1 to 10# of the CPU, and the channel decoding is performed in the CPU. After removing the error correcting code source and obtaining the actual control information, the recovered voice data flows through the data line and the address line. The generated digital voice signal is sent from 78# of U80 1 to 8# of PCM decoder U803. The digital voice signal is decompressed and A/D converted in PCM decoder, then the received signal and volume are adjusted by digital volume locator, and then the analog audio signal is output from 4# of U803 to 6# and 2 1# of U900. After the ringing signal of the 6# input is amplified by the internal ringing driver, the 4# and 5# outputs of U900 drive the ringer to send the inter-tone signal, the 2 1# input, and the amplified voice signals from 19# and 20# output drive the receiver to sound. When our users are on the phone, the voice is converted by the receiver and sent to the 9# terminal of the power integrated circuit U0-. After internal audio amplification, the amplified analog audio signal is output from the 10# terminal. The signal is sent to the PCM codec U803 of 18#, and the pulse code modulation is completed inside U803. The PCM signal output by 13# is sent to the 89# speech encoder of 80 1, and the speech data line and address line are fed into U80 1, and the speech data stream is loaded into the central processor U70 1. After the channel coding of the voice data stream is completed in U70 1, the 1 1# after U70 1 is sent to the 4# of the modem U50 1, and the signal is subjected to D/A conversion and encryption processing in U50 1. At the same time, 48# of 32D54 is connected to the positive pole of power supply. At this time, if we press the power-on key again, the 24# of U900 will become low level, and the four voltages stably output by U900 are R275V, L2.75V, R4.75V and L5.0V respectively. The 30th # generates a reset signal, and the 27th # generates an application start signal. The 13MHz clock oscillator consisting of 32D53 and 13MHz crystal and transformer diode * * generates the 13MHz clock, which is shaped and amplified in the 32D53, and then output from 59 # to 17# of the buffer interface circuit U703, and then sent to 57 # of the CPU from 37 # of U703. In addition, the collector voltages of Q202 and Q203 are both 2.75V, which supplies power for the receiving or transmitting circuit inside 32D53. L5.0V sent by No.3 U900 supplies power to the negative voltage generating circuit. Version, SIM card and PCM codec U803 are also powered by L5.0V The voltage of R2.75V from U900 No.28 supplies power to all logic modules. The voltage of 2.75V sent by U900 on 28th is supplied to the RF part. The R4.75V voltage sent by U900' s 4 1 # generates power for the transceiver intermediate frequency circuit 32D53, and the VXW conversion voltage output by U900' s 37 # supplies power for the emitters of Q202 and Q203. Because the model of the mobile phone is different from the manufacturer, the working principle mentioned above may not be applicable to some mobile phones, but the general workflow should be the same.