TCL T728 Service Manual
TCL Mobile Communication
CO., Ltd
第
21
页
共
32
页
pieces of audio signal outputted from CPU MT6205. One of them is sent to the
Spe&Rec for making voice tone directly after passing through a filtering network
composed by L1. The other ring tone signal will be amplified by an audio amplifier
LM4990 ,and then sent to
Spe&Rec for making ring tone
3.7.2 Microphone circuit
After the voice tone is transferred into a electronic-audio signal inside of a Mic, the
audio signal will be filtered in a fi
ltering network composed by L202
、
L203
、
C218
、
C219 ,coupled by C209
、
C211 ,processed by CPU MT6205 (entered this unit from its A10 and
B10 pin ). In the following diagram, the MICBIAS is for offering a bias voltage for Microphone
circuit.
3.8 LCD displaying circuit
The T728 is a phone with a black and white LCD, which have a simple displaying circuit. The
LCD is 128*64 pixel, black and white.
3.9 SIM Card circuit
The function of SIM card circuit is to found a circuit, which makes it possible to pass signal
between CPU and SIM card, also make it possible to pass information between handset and
network by offering all kinds of preferences needed by network (so that the network can recognize
the user and offer relative business. The SIM card circuit is also simple. Next, here is showing the
function of every pin of SIM card. The Vcc pin offers electric power for the SIM card circuit. The
RST is a pin of reset. The CLK pin offers the system clock signal. The I/O stands for in and out.
The VPP connects with a high level. The GND connects to the ground.
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