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This lesson talks about the connection channels of the 4G frequency bands

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of the three major platforms in the circuit diagram

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This section is about the Redmi K50, which is the 4G frequency band receiving

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and transmitting channels of the MediaTek platform.

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Let's first open the frame diagram of this model

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This is the frequency band used by China Unicom and China Telecom

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This is the frequency band used by China Unicom and China Telecom

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Its antenna is this one A N T 5 is the fifth antenna

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Why are we looking for this J0114?

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MHB is the middle and high frequency band

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And what we are looking for is B1, B1, they also belong to the mid-band, so we are looking for this antenna

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Of course, in this mobile phone, its 4G mid-band is not limited to this one antenna

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We just find the channel for one of the antennas

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Receive from Antenna to Antenna Mount J0114

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The antenna induces high-frequency electromagnetic waves and turns them

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into high-frequency electrical signals to the antenna base

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This high-frequency receiving signal will continue to go through the J0304 normally closed contact

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Pin 2 and pin 1 of the normally closed contact are always on

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Its use is mainly for factory testing, and under normal circumstances,

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the second pin and the first pin are a conductive line

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Continue to go after receiving the signal through the normally closed contact

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Its name has changed, there is a 3P3T three-knife three-throw switch

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Let's keep watching

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This received signal passes through a filter to filter out some unwanted clutter

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Only keep some signals of the frequency bands we need in the past

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After the received signal passes through the filter, it reaches the three-knife three-throw switch

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It's actually a toggle switch for the antenna.

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Usually we can also call it a small antenna switch

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After reaching the three-knife three-throw switch, the 6-pin and 12-pin of the switch are turned on

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Arrived at another three-pole three-throw switch

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It has three internal line channels

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The small RF switch of S0401 is also called a small antenna switch. Its 4-pin and 12-pin conduction

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The receiving signal continue walking, and its name changes

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This receive signal goes on

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Before the received signal reaches the RF transceiver chip, it must amplify the power of the received signal

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This receive signal reaches U0700 to pin 57

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Internally amplifies the power of the received signal

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After amplification, the PRX signal is output from pin 45 and pin 46, which is the received signal

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Then the received signal power is amplified

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The amplified received signal is sent to the G22 and F21 pins of the RF transceiver U1300

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Then the radio frequency transceiver mixes this frequency band signal containing very high frequency

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Remove the carrier and demodulate the DL signal

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This DL signal, we can also regard it as belonging to the received data

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This bus is actually the QLINK bus

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The DL pin sends the received data to the big CPU, which is actually to the baseband CPU part in the big CPU.

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The baseband CPU performs a series of processing such as final demodulation on the received signal

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This is its receiving channel

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Then launch is a reverse process

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Transmission is the output of mobile phone data

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In the process of checking its launch channel, we can also start from the big CPU

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Where do the big CPU slots start?

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Just look for the UL signal of the QLINK bus

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UL is called uplink, which belongs to the signal of transmitting mobile phones

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It transmits some data that is emitted

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The large CPU output is sent to the radio frequency U1300, and the U1300 generates high-frequency carrier waves

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Because this UL signal is a low frequency signal

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For example, it contains some data that the mobile phone needs to communicate with the base station

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But this low-frequency signal cannot be transmitted quickly and long-distance in the air,

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only high-frequency signals have this property

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At this time, the radio frequency transceiver generates a high-frequency carrier wave in its own circuit

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Put some data of this low frequency including our mobile phone on the high frequency carrier

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After being loaded, it is output from the launch channel

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At this time, it is necessary to find the transmission code of the medium frequency band,

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and there is also a line with the code name of MB

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Since B1 belongs to M B, it is necessary to find this route

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After the U1300 mixes and up-converts, it forms high-frequency signals in these frequency bands

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These transmit frequency band signals have been formed,

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and it will be handed over to the transmit power amplifier, that is, the PA power amplifier.

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Give it to the power amplifier inside the U0700, the power amplifier performs power amplification,

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Then the transmit signal continues to go from the antenna terminal pin of the power amplifier

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Continue to go through the 3-pole 3-throw switch to reach the filter

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Pins 1 and 3 of the filters conduct and then it reaches the normally closed contact

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It ends up at the antenna terminal

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The transmitted signal is transformed into a high-frequency electromagnetic wave

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through the antenna and transmitted into the air, and the base station receives it

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When checking this line, we will use the previous knowledge

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B1 belongs to the mid-band, we will look for MB

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When looking at the launch, we need to know what frequency band to look for

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What frequency range does this frequency band belong to?

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B1, B3, B2, B4, B25, B34, B39, they are all mid-band

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Also note that there is a distinction here. PRX is the main set of receivers, which is what we usually look for.

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TX is transmit

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We also have to know that the receiver must be amplified by the receiver to reach the radio frequency

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If the transmission wants to reach the antenna end,

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it must go through the power amplifier when it comes out of the radio frequency

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That's all for this lesson