LG HB620, Руководство по обслуживанию

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Only for training and service purposes
3. TECHNICAL BRIEF
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3.2 GSM Mode
3.2.1 GSM Receiver
The Dual-mode HB620T’s receiver functions are operated by only one RFIC as follows:
■
EGSM-900, DCS-1800, PCS-1900 and UMTS-2100 modes use the RTR6275 IC only. Each mode
has independent front-end circuits and down-converters, but they share common baseband circuits
(with only one mode active at a time). All receiver control functions are beginning with SBI
2 -
controlled parameters.
RF Front end consists of antenna, antenna switch module (LSHS-M090UH) which includes three RX
saw filters (EGSM-900, DCS-1800 and PCS-1900). The antenna switch module allows multiple
operating bands and modes to share the same antenna. In HB620T, a common antenna connects to
one of six paths: 1) UMTS-2100 Rx/Tx, 2) EGSM-900 Rx, 3) EGSM-900 Tx, 4) DCS-1800 Rx, and 5)
DCS-1800, PCS-1900 Tx(High Band Tx’s share the same path), 6) PCS-1900 Rx. UMTS operation
requires simultaneous reception and transmission, so the UMTS Rx/Tx connection is routed to a
duplexer that separates receive and transmit signals. GSM900, DCS1800, and PCS1900 operation is
time division duplexed, so only the receiver or transmitter is active at any time and a frequency
duplexer is not required.
The GSM900, DCS1800, and PCS1900 receiver inputs of RTR6275 are connected directly to the
transceiver front-end circuits(filters and antenna switch module). GSM900, DCS1800, and PCS1900
receiver inputs use differential configurations to improve common-mode rejection and second-order
non-linearity performance. The balance between the complementary signals is critical and must be
maintained from the RF filter outputs all the way into the IC pins.
Since GSM900, DCS1800, and PCS1900 signals are time-division duplex (the handset can only
receive or transmit at one time), switches are used to separate Rx and Tx signals in place of frequency
duplexers - this is accomplished in the switch module.
2 The RFIC operating modes and circuit parameters are MSM-controlled through the proprietary 3- line Serial Bus Interface (SBI). The Application
Programming Interface (API) is used to implement SBI commands. The API is documented in AMSS Software - please see applicable AMSS
Software documentation for details.
ANT_SEL0 ANT_SEL1 ANT_SEL2
EGSM TX HIGH HIGH LOW
DCS/PCS TX HIGH LOW LOW
UMTS2100 HIGH LOW HIGH
EGSM RX LOW LOW/HIGH LOW
DCS RX LOW HIGH HIGH
[Table 3.1] Antenna Switch Module Control logic
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