Off-Chip Rf Components - LG TU550 Service Manual

3. TECHNICAL BRIEF

3.5 Off-chip RF Components

3.5.1 Antenna switch module (U100 : CXG1198AEQ)
The antenna switch module allows multiple operating bands and modes to share the same antenna. In
the TU550 design, a common antenna connects to one of eight paths: 1) UMTS-850 Rx/Tx, 2) UMTS-
1900 Rx/Tx, 3) GSM-850 Rx, 4) GSM-900 Rx, 5) GSM-850/GSM-900 Tx(Low Band Tx's share the
same path), 6) DCS-1800 Rx, and 7) DCS-1800,PCS-1900 Tx(High Band Tx's share the same path),
8) 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. GSM band of
operation is time division duplexed, so only the receiver or transmitter is active at any time and a
frequency duplexer is not required. The module includes lowpass filters for the GSM bands transmit
paths to reduce out-of-band emissions, PA harmonics in particular.
3.5.2 UMTS duplexer (FL106_
A UMTS duplexer splits a single operating band into receive and transmit paths. Important performance
requirements include;
-. Insertion loss . this component is also in the receive and transmit paths ; In the TU550 typical losses :
UMTS1900_ Tx = 2.1 dB, UMTS1900_ Rx = 2.8 dB and UMTS850_ Tx =1.9 dB, UMTS850_ Rx = 2.7 dB
-. Out-of-band rejection or attenuation . the duplexer provides input selectivity for the receiver, output filtering for
the transmitter, and isolation between the two. Rejection levels for both paths are specified over a number of
frequency ranges. Two Tx-to-Rx isolation levels are critical to receiver performance:
-. Rx-band isolation . the transmitter is specified for out-of-band noise falling into the Rx band. This noise leaks
from the transmit path into the receive path, and must be limited to avoid degrading receiver sensitivity. The
required Rx-band isolation depends on the PA out of-band noise levels and Rx-band losses between the PA
and LNA. Minimum duplexer Rx band isolation value is about 45 dB.
-. Tx-band isolation . the transmit channel power also leaks into the receiver. In this case, the leakage is outside
the receiver passband but at a relatively high level. It combines with Rx band jammers to create cross-
modulation products that fall in-band to desensitize the receiver. The required Tx-band isolation depends on the
PA channel power and Tx-band losses between the PA and LNA. Minimum duplexer Tx-band isolation value is
about 55 dB.
-. Passband ripple . the loss of this fairly narrowband device is not flat across its passband. Passband ripple
increases the receive or transmit insertion loss at specific frequencies, creating performance variations across
the band.s channels, and should be controlled.
-. Return loss . minimize mismatch losses with typical return losses of 10 dB or more (VSWR <2:1).
-. Power handling . high power levels in the transmit path must be accommodated without degraded
performance. The specified level depends on the operating band class and mobile station class (per
the applicable standard), as well as circuit losses and antenna EIRP. Several duplexer
characteristics depend upon its source and load impedances. QUALCOMM strongly recommends an
isolator be used between the UMTS PA and duplexer to assure proper performance.
LGE Internal Use Only
: ACMD7402 , FL107_
UMTS1900
- 28 -
: B7637 )
UMTS850
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