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This lesson goes on to talk about the GSM 900 call channel of Xiaomi mobile phone

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Find the schematic diagram of Mi 10 Pro, and then go to the next lesson

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GSM 900 reaches U0600 from the antenna end,

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this is the low-band power amplifier plus antenna switch

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The internal 2 pin of the antenna switch lead to 44 pin

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The reception of GSM900 is also the reception of B8

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Let's keep watching

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Because it is a receiving signal, before the receiving signal reaches the RF transceiver,

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it must go to the receiving amplifier chip

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Double click it

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It reaches a capacitor, and after the coupling of the capacitor, it is given to the G1 pin of a chip

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This chip is called U1000

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This chip internally amplifies the power of the received signal

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After it reaches the G1 pin, there are groups, there are two groups of receiving amplifiers,

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and one group of receiving amplifiers

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Here is LNA1, here is LNA2

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LN1 corresponds to OUT1, which is GSM900

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It comes in from the G1 pin and goes out through the D4 pin after zooming in

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The amplified received signal is bound to the RF transceiver

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When we see this SDR, we can also expect that its next chip is a radio frequency transceiver

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Double click it

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GSM900 has reached the A8 pin of a chip SDR865

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The chip is a Qualcomm radio frequency transceiver

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After reaching pin A8 of this RF transceiver

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This radio frequency generator removes the high-frequency carrier wave of about 900 megabytes,

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and only retains the initial demodulated voice signal

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So where does the demodulated voice signal go, it is not described here

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It is described in the third part of the RF transceiver, called the Q LINK bus

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This Qlink bus is to the baseband CPU

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Here is the radio frequency transceiver

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Let's look at its line

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If we just find a DL, we can find the baseband CPU that leads to it, U1601

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This is the analog signal part of the baseband CPU

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Because this Qlink signal is an analog signal

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This chip is called SDX55M, which is a baseband CPU of Qualcomm

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This is the receiving channel line of Xiaomi's GSM900

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When we look for the line, we can find this baseband.

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That's all for this lesson