LG KF600w Service Manual page 34

2.3 Circuit Description
2.3.1 Keypad/LCD and Receptacle Part
Once the keypad is pressed, the key signals are sent out to MSM6550 for processing. In addition, when the key is
pressed, the keypad/LCD lights up through the use of 7 LEDs. The terminal status and operation are displayed on the
screen for the user with the characters and icons on the LCD.
2.3.2 Audio Processing Part
MIC signals are amplified through OP AMP, inputted into the audio codec (included in MSM6550) 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
MSM6550 activate the ringer by using signals generated in the timer in MSM6550.
2.3.3 MSM Part
MSM6550 is the core element of CDMA system terminal that includes ARM926EJ-S microprocessor core. It
supports both CDMA and Digital FM, operating in both the cellular and PCS spectrums. The subsystems within the
MSM6550 include a CDMA processor, a DFM processor, a multi-standard Vocoder, an integrated CODEC with
earpiece and microphone amplifiers, general-purpose ADC for subsystem monitoring, an ARM926EJ-S
microprocessor, and Universal Serial Bus(USB) 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 MSM, 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.