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This lesson talks about the GSM 900 call channel of Xiaomi mobile phone
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The GSM 900 channel, we regard it as the calling channel of China Mobile card
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Let's take a look at its launch channel
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Its transmission channel is from the baseband CPU to the radio frequency,
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to the low-band power amplifier, to the filter, to the small antenna switch,
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to the coaxial switch, to the antenna
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Open its drawing
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The source of the transmitted signal is from the baseband
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The baseband modulates the voice-containing signal sent by the CPU,
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and then sends it to the radio frequency from the uplink after modulation.
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We double click it
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It reaches the third part of the RF transceiver U1301
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When it comes to its R36, R35, R28, P29, this is an uplink transmission signal
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After arriving here, the radio frequency transceiver itself generates a high-frequency carrier wave,
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carries the voice signal on it, and finally transmits it out
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There are a lot of launching pins here
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There is a high frequency of transmission, definitely not GSM 900,
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GSM 900 belongs to the low frequency band
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After the RF transceiver is mixed and converted, it is output from the A32 pin,
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and it must reach the power amplifier for power amplification
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You can see after double-clicking it, it goes to a capacitor, goes through an inductor
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GSM 900 continues to go, reaching pin 24 of chip U0600
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What chip does this chip belong to?
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It is called a low-band antenna switch plus power amplifier,
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in fact, it also includes a 2G power amplifier
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After the GSM 900 comes in, after being amplified inside the power amplifier,
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it reaches the antenna end through the 2-pin output
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This is the low frequency antenna
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The transmit signal continues to go, to the 2 pin of the filter, and then to the LB ANT
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Of course this is not the end of the antenna
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We double click it
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It goes to pin 6 of a small RF switch S0308
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RF2 and RF4 inside the switch are turned on
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The transmit signal reaches the antenna end from pin 8, and then reaches pin 8 of a filter
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Then output from pin 3 to this coaxial switch
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Pin 2 and pin 1 of the coaxial switch are always on
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The transmit signal has reached the ANT0 LMH
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It conducts through the coupling of two 0 ohm resistors,
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and then through the coupling of capacitor C0218, finally reaches the antenna base J0204
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Antenna mounted on the antenna pedestal
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The antenna turns the high-frequency electrical signal of GSM 900 into electromagnetic waves,
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transmits them into the air, and the base station can receive them
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This is the transmission line of the GSM 900 signal from the baseband to the antenna of Xdiaomi 10 Pro
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That鈥檚 all for this lesson
