LG VX8560 Service Manual page 44

VX8560
2.3 Circuit Description
2.3.1 Keypad/LCD and Receptacle Part
Once the keypad is pressed, the key signals are sent out to QSC6075 for processing. In addition, when the key is
pressed, the keypad lights up through the use of 2 LEDs. The terminal status and operation are displayed on the
screen for the user with the characters and icons on the LCD.
Moreover, it exchanges audio signals and data with external sources through the receptacle, and then receives power
from the battery or external batteries.
2.3.2 Audio Processing Part
MIC signals are amplified through OP AMP, inputted into the audio codec(included in QSC6075) and converted into
digital signals. Oppositely, digital audio signals are converted into analog signals after going through the audio codec.
These signals are amplified at the audio amplifier and transmitted to the ear-piece. The signals from QSC6075
activate the ringer by using signals generated in the timer in QSC6075.
2.3.3 MODEM Part
QSC6075 is the core element of CDMA system terminal that includes ARM926 EJS microprocessor core. It supports
both CDMA and GPS, operating in both the cellular and PCS spectrums. The subsystems within the QSC6075
include a CDMA processor, a multi-standard Vocoder, an integrated CODEC with earpiece and microphone
amplifiers, general-purpose ADC for subsytem monitoring, an ARM926 EJS microprocessor, and both Universal
Serial Bus(USB) and an RS-232 serial interfaces supporting forward and reverse link data communications of 307.2
Kbps simultaneously. And it also contains complete digital modulation and demodulation systems for CDMA
standards, as specified in IS-95-A/B/C.
In QSC, coded symbols are interleaved in order to cope with multi-path fading. Each data channel is scrambled by
the long code PN sequence of the user in order to ensure the confidentiality of calls. Moreover, binary quadrature
codes are used based on walsh functions in order to discern each channel. Data created thus are 4-phase modulated
by one pair of Pilot PN code and they are used to create I and Q data.
When received, I and Q data are demodulated into symbols by the demodulator, and then de-interleaved in reverse to
the case of transmission. Then, the errors of data received from viterbi decoder are detected and corrected. They are
voice-decoded at the vocoder in order to output digital voice data.
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