How does a mobile phone make calls and send text messages?

1. The working principle of mobile phones: Generally speaking, we ordinary users only need to learn how to use mobile phones well, and there is no need to delve into its specific working principles; however, in the process of using mobile phones, due to Affected by various factors, mobile phones will inevitably malfunction. If every time you encounter even the smallest malfunction, you have to send it to a professional repair shop for repair, you may find it troublesome. If you have considerable electrical knowledge, you may want to learn to repair it yourself, but to learn to repair it, you must first be familiar with the working principle of the mobile phone. Only in this way can you determine the cause of the malfunction and find the corresponding solution. At the same time, understanding the working principle of mobile phones can also serve as a reserve of knowledge for ordinary people. In order to help these users who love mobile phones learn to repair quickly, the author will use Motorola mobile phones as an example to introduce in detail how mobile phones work. The author believes that the reason why mobile phones can communicate with each other is the result of the coordinated work of three parts. These three parts are the radio frequency part, the logic part and the power part. To understand the working principle of mobile phones, you only need to understand how these three parts work. Okay, now the author will introduce the working principles of these three parts separately. Radio frequency part Usually the radio frequency part is composed of a signal receiving part and a signal transmitting part. When the mobile phone receives a signal, it first uses the antenna to pass the received 935-960MHz radio frequency signal through U400 and SW363 to separate the transmitted signal and the received signal so that the sending and receiving do not interfere with each other. Input the fifth pin output from the fourth pin of U400 and enter the receiving front-end loop. The working status of U400 is controlled by the potential of the third pin, which in turn is controlled by the TXON and RXON signals from the CPU. The RF signal passing through the antenna switch is first filtered by the bandpass filter FL451, and then sent to the high-frequency amplifier tube Q418 for amplification. The output of Q418 is filtered by FL452 and sent to the Q420 mixing tube for mixing. The local oscillation signal is generated by RXVCO, and is filtered by FL453 before being sent to the base of Q420 for mixing. Taking the difference, a 153MHz intermediate frequency signal is output from the collector of Q420. After filtering by FL420, a 153MHz pure medium-frequency diesel engine signal is obtained. Now it is amplified by Q421 and sent to pin 31 of U201. The 153MHz IF signal and the 153MHz carrier signal are demodulated in 32D53 to generate RXI and RXQ analog baseband signals, which are sent to 14# and 15# of U501 via 46# and 48# of U201. After A/D conversion in U501, it is sent to a digital signal processor for further processing. The 153MHz carrier wave consists of U201's 41#, 42#, and 43# connected to a 306MHz oscillation circuit composed of peripheral circuits to form a 306MHz Hui wave signal, which forms a 153MHz carrier wave after the second frequency. For the transmitting part, the TXIN, TXIP, TXQN, and TXQP transmit frequency band signals output from 21#, 22#, 23#, and 24# of 501 enter 61#, 62#, 63#, and 64# of U201. 6#, 7#, and 10# of U201 are externally connected to a 216MHz VCO to generate a 216MHz carrier signal. This signal is divided by the frequency divider in U201 to generate a 108MHz transmit intermediate frequency signal. The four modulated signals complete 108MHz carrier modulation in U201 and are output from pin 4 to 4# of U300. U300 completes the transmission of the sampling signal and the TXVCO phase gentle frequency, and takes the difference to get the 108MHz signal and the TXIF phase of the 4# input to generate a phase detection error voltage, which is output from the 8th pin to control the capacity of the varactor diode CR300 to change the oscillation of the TXVCO Frequency, the 890-915MHz transmit signal output from the C pole of Q300 is amplified by the Q301 preamplifier and driven by Q302, and then enters the power amplifier Q302. The amplified signal enters the first pin of the antenna U400, and then is emitted from the 4# sending antenna of U400. Logic part In the logic part, the received RXI and RXQ analog baseband signals complete D/A conversion, decryption and adaptive equalization inside the modem U501, and then the digital baseband signal is sent from 6# of U501 to 10# of the CPU, and is processed in the CPU. After channel decoding, error correction code source and real control information are removed, the recovered voice data flows through the data line and address line and is sent to the voice unit U801 for decoding.

The generated digital voice signal is sent from 78# of U801 to 8# of PCM decoder U803. The digital voice signal completes pressure reduction and A/D conversion in the PCM decoder, and then passes through the digital volume positioner to adjust the received signal and volume. Then the analog audio signal is output from U803's 4# to U900's 6# and 21 #. The ringing signal input from 6# is amplified by the internal ringing driver and drives the ringer to send audio signals from the 4# and 5# outputs of U900. It is input from 21# and passes through the internal audio amplifier. 19# and 20# output amplified voice signals to drive the earpiece to sound. When our user is speaking, the voice is sent to 9# of the power integrated circuit U0- after being converted by the earpiece. After being amplified by the internal audio, the amplified analog audio signal is output from 10#. The signal is sent to 18# of PCM codec U803 and PCM encoding is completed inside U803. The PCM signal output from 13# is sent to 89# of the speech encoder 801. The voice data line and address line are inserted into U801 to flow the voice data to the central processor U701. After U701 completes the channel coding, the voice data flow passes through U701 11# is sent to the 4# of the modem U501. After the signal undergoes D/A conversion, encryption and other processing in U501, the generated four-way modulated signals TXIP, TXIN, TXQP and TXQN are sent to the transceiver intermediate frequency circuit U201. To generate and transmit intermediate frequency ITX and IF signals. As for the power supply part, once we install the battery on the mobile phone, the electronic Q999 is connected; at the same time, the 48# of the 32D54 is connected to the positive pole of the power supply. At this time, if we press the power button again, the 24# of the U900 becomes low level. The four stable output voltages of U900 are R275V, L2.75V, R4.75V, and L5.0V. No. 30# generates a reset signal and No. 27# generates a boot application signal. The 13MHz clock oscillator is composed of 32D53, 13MHz crystal and transformer diode to generate a 13MHz clock. After internal shaping and amplification in 32D53, it is sent from the 59# output to the 17# of the buffer interface circuit U703, and from the 37# of U703 Send the CPU's 50# to send the boot maintenance signal to the U900's 29# to maintain normal booting. In addition, the collector voltages of Q202 and Q203 are both 2.75V, which supply power to the internal receiving or transmitting circuit of 32D53. The L5.0V sent by U900 No. 3 supplies power to the negative voltage generating circuit. Version, SIM card and PCM codec U803 are also powered by L5.0V. The R2.75V voltage sent by U900 No. 28 supplies power to all logic modules. The 2.75V voltage sent out by U900 No. 28 is supplied to the RF part. The R4.75V voltage sent by U900 No. 41 supplies power to the transceiver IF circuit 32D53, and the VXW conversion voltage output by U900 No. 37 supplies power to the emitters of Q202 and Q203.