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Q120 TV Maintenance Manual
4
1.2 Detailed Description of Circuit Chart
1.3 RF circuit
This phone is designed on MTK6252 platform. RF main chip is intergraded into
MT6252, PA use
RPF88162B-TB
, TCXO uses 26MHz crystal oscillator.
(1) Receiving circuit
The GSM or DCS signal received from a base station via antenna is inputted from
the pin U102 27, and sent to MT6252. The signals are amplified by their own
low-noise amplifier (LNA). The amplified signal is sent to a down converter, where
the signal is mixed with local oscillation (LO) output from RX VCO to generate zero
intermediate frequency (ZIF) signals. The zero-IF signal passes through a filter and is
amplified by programmable gain amplifier (PGA), then the signal is outputted to I and
Q demodulator to generate I/Q base band signals. The demodulated I and Q base band
signals are outputted to the base band part for further processing.
(2)
Transmitting circuit
A transmitter consists of I/Q modulation circuit, up-conversion mixer circuit,
power amplifier and duplex switch. The I/Q signal is inputted to be performed signal
modulation as the modulation signal. The modulated TXIF signal restrain its third
harmonic by harmonic suppression filter. The follow-up TXIF signal will be sent to a
discriminator on the offset frequency phase lock loop (OPLL). Then perform
射频
PA
U102
高频滤波
器
U103
CPU
U201
摄像头
按键板
马达
SIM
卡
SIM
卡
切换
开关
麦克
扬声器
LCD
蓝牙
FM
RF PA+switch
U102
High Frequency Filter
U103/U104/U105
SIM card
Switch
Blue Tooth
Speaker
MIC
Camera
Keypad
Board
Motor
CPU
U202
SIM card
Summary of Contents for Q120 TV
Page 3: ...Q120 TV Maintenance Manual 3 1 Circuit diagram instruction 1 1 Main board explored view...
Page 6: ...Q120 TV Maintenance Manual 6 1 5 Function circuit FM circuit U802 FM receiving chip RDA5802E...
Page 7: ...Q120 TV Maintenance Manual 7 BT circuit U701 BT receiver chip MT6612CN L...
Page 10: ...Q120 TV Maintenance Manual 10 3 2 No ring tone...
Page 11: ...Q120 TV Maintenance Manual 11 3 3 LCD display fault...
Page 12: ...Q120 TV Maintenance Manual 12 3 4 Charging fault...
Page 14: ...Q120 TV Maintenance Manual 14 3 6 Fail to identify SIM card...
Page 15: ...Q120 TV Maintenance Manual 15 3 7 MIC fault...
Page 18: ...Q120 TV Maintenance Manual 18 3 10 Vibrate fault...
Page 19: ...Q120 TV Maintenance Manual 19 3 11 FM fault...
Page 23: ...Q120 TV Maintenance Manual 23 3 15 Unable to use USB END...