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This lesson talks about the relevant circuits of the handset of MediaTek

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Our example is Redmi K50, which uses MediaTek's CPU solution

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Xiaomi 12 uses Qualcomm's CPU, but their audio circuits are similar

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Let's take a look

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This is the earpiece shrapnel

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Here is the small audio, SMARTPA

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This is a stereo receiver, that is, the receiver can replace the speaker, it has the function of a speaker

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Speakers can play music

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What does it do when it's not playing music?

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When we don't turn on the hands-free, this speaker will make a sound

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It is exactly the same as the driver circuit of the speaker

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Including the small audio chip that drives the handset, all of the same model

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This is a small audio, also called an audio amplifier

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The sound signal is transmitted between the CPU and the small audio through the I2S3 bus

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The code name of the handset is SPKR, which is the same as the code name of the speaker

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Its circuit working process is like this

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When making a call, the sound signal is transmitted from the radio frequency to the baseband,

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the baseband is transmitted to the CPU,

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and the CPU is transmitted to the small audio through the I2S3 bus.

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Small audio converts it to digital-to-analog conversion, and then performs power amplification after conversion

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After the power is amplified, the audio signals for driving the handset are output

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from these two lines to make the handset emit sound

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So we can hear each other

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This is when the speakerphone is off

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The handset only works when the handsfree is not turned on

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Stereo just adds a new feature

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The earpiece is driven by small audio, and its power can become very large

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When it gets loud, it can act as a speaker to play music

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Let's look at this older model, MTK's Changxiang 20 Pro

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It's an early cell phone, it's not stereo, the main audio drives the handset

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Its earpiece code name is EAR

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We want to find the earpiece circuit, first search for EAR

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Changxiang 20 Pro uses MediaTek's solution, and the power supply includes the main audio

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Earpiece with large audio driver does not support music playback

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The handset is the handset, it only makes a sound when the speakerphone is not turned on

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Let's look at the main audio inside the power supply

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It uses MOSI bus and MISO bus to transmit data between it and the main CPU

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One is output and the other is input

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And each has three sets of data, 0, 1, 2

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This is the handset circuit of Changxiang 20 Pro and Redmi K50,

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one is an early model and the other is a modern model, both of which use MediaTek solutions

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That's all for this lesson