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input I.Q mixer (which contains high/low paratactic two mixer part), mix with surge signal caused by local
oscillator in U104, these surge signals must match the currently working frequency of mobile phone. Modulate
them into four low frequency I.Q signal around 100KHz after mix (there is phase relation in these four paths of
signal). Second, I.Q must input in low pass filter for eliminate syntonic interfere. After this process, input signals
into channel filter. Channel filter is a five-class belt passes filter with self adjust function. Its center frequency is
100KHz. For avoid leading distortion caused by signal attenuated too much after many times sieve, before
sieve, it should match 8dB step magnify for each class. Signals after sieve match 4dB step magnify for
compensate direct current excursion. Finally, these signals input intermediate frequency buffer waiting for input
U201 ABB which will manage them.
I.Q signal is transfer into digital signal by ADC when input in ABB, then output from ABB to U201 DBB.
DBB do farther digital sieve to these signals, GMSK demodulating, complect removing, decoding, channel
decoding, PCM decoding etc. voice decode arithmetic manage. Then the signals passes VSP port (Voiceband
serial port) between U201 and U202 into U202 and managed by DAC in U202. Finally, analogy signal are sent
to earphone or headphone and transfer them into voice signal.
7.5: RF manage circuit----transmit circuit:
As the picture shows: transmit circuit is made up of: DBB(U201)
、
ABB(U202)
、
Transceiver(U602)
、
PA(U603)
，
RF-Switch(FE600)
，
RF-Connector(CN600)
，
Antenna etc.
Voice signal from user is transmit into analogy electronic signal, and then input in ABB U202. After
transferred by ADC in U202, pass VSP port into DBB U201. In U201, signals will be impulse sampling, PCM
coding, channel coding, coding, complecting, GMSK modulating etc. voice demodulating manage, and then
pass BSP path into ABB U202. Managed signals by DAC in ABB, divided into four paths of analogy base band
I.Q signal after passing low frequency filter. Finally, input these signals into transceiver U602
In U602, base band signal is modulated to transmit intermediate frequency by I.Q modulation. This I.Q
modulation with low harmonic wave distortion, low carrier wave divulge, high syntonic interference restrain etc.
can reduce phase error furthest. Then pass high frequency modulate, signal are modulated to final frequency
needed. Finally, the signals are sent to PA for magnifying.
Summary of Contents for W420
Page 1: ...Voxtel Repair Manual Item W420 ...
Page 23: ...23 3 LDO circuit ...
