Gsm Mode - LG KF700Q Service Manual

3. TECHNICAL BRIEF

3.2 GSM Mode

3.2.1 GSM Receiver
The Dual-mode KF700Q's receiver functions are operated by only one RFIC as follows:
■ GSM850, EGSM-900, DCS-1800, PCS-1900 and UMTS-2100 modes use the converters, but they
share common baseband circuits (with only one mode active at a time). All receiver control functions
are beginning with SBI
RF Front end consists of antenna, antenna switch module (D5015) which includes three RX saw filters
(GSM850, EGSM-900, DCS-1800 and PCS-1900). The antenna switch module allows multiple
operating bands and modes to share the same antenna. In KF700Q, a common antenna connects to
one of eight paths: 1) UMTS-850 Rx/Tx, 2) UMTS-2100 Rx/Tx, 3) GSM850 Rx, 4) EGSM-900 Rx, 5)
DCS-1800 Rx, 6)PCS-1900 Rx, 7) GSM850, EGSM-900 Tx (Low Band Tx's share the same path) and
8) DCS-1800, PCS-1900 Tx(High Band Tx's share the same path).UMTS operation requires
simultaneous reception and transmission, so the UMTS Rx/Tx connection is routed to a duplexer that
separates receive and transmit signals. GSM850, EGSM900, 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.
GSM850/EGSM900 TX
DCS1800/PCS1900 TX
WCDMA850
WCDMA2100
GSM850 RX
EGSM900 RX
DCS1800 RX
PCS1900 RX
The GSM850, EGSM900, DCS1800, and PCS1900 receiver inputs of RTR6280 are connected directly
to the transceiver front-end circuits(filters and antenna switch module). GSM850, EGSM900,
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 GSM850, EGSM900, 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.
The RFIC operating modes and circuit parameters are MSM-controlled through the proprietary 3- line Serial Bus Interface (SBI). The Application
2
Programming Interface (API) is used to implement SBI commands. The API is documented in AMSS Software - please see applicable AMSS
Software documentation for details.
LGE Internal Use Only
-controlled parameters.
2
ANT_SEL0
HIGH
HIGH
LOW
LOW
LOW
LOW
LOW
LOW
[Table 3.1] Antenna Switch Module Control logic
- 18 -
ANT_SEL1 ANT_SEL2
HIGH LOW
LOW LOW
HIGH LOW
LOW HIGH
HIGH HIGH
LOW HIGH
HIGH LOW
LOW LOW
Copyright © 2008 LG Electronics. Inc. All right reserved.
Only for training and service purposes
ANT_SEL3
LOW
LOW
HIGH
HIGH
LOW
LOW
LOW
LOW