Blu LIFE 8, Service Manual, Page: 13 / 29

3.2 TX Part troubleshooting
3.2.1 TX process analysis
The TX circuit is composed of two parts
，
modulation and power amplify circuit.
The modulation circuit is composed of transceiver IC (MT6166). The power amplify circuit
is include PA IC (SKY77590).
First, Voice be converted to electric signal by microphone then input CPU IC
After A/D (analog signal convert to digital signal) in CPU, became 64kbits/s dataflow, then
going channel encode to 13kbits/s numerical audio dataflow, system encode
again ,dataflow became 22.8bits/s, these processes were processed in DSP section. Then
the dataflow pass D/A converter, output four signals (I&Q I,IB,Q,QB) from CPU to
transceiver IC.
The I/Q signals come into the MT6166 and then are modulated into RF signals after going
through the PLL circuit and mix frequency circuit, then amplify the RF signal. The RF
signals are sent out to PA (SKY77590).
Transceiver IC block diagrams as flow:
After sent into the SKY77590, the signals are amplified and transmitted as the
electromagnetic wave by the antenna after passing through the ASM(antenna switch
module) witch in PA(SKY77590).
PA is controlled by the way of voltage which from CPU. It’s used to amplify the power of
the signals according to the requirements of the system. The power of the signals is
amplified to different levels by VAPC (Vramp) control pin. The power level of the GSM
TX signal is at 5 to19, 3.2mW to 2W; The DCS is at 0 to15, 1mW to 1W. The TX_EN will
control the working state of the PA chipset, The PA’s working states is not continuous.
IQ signal from CPU to TC
Modulation, mix, filter and amplify
PA