LG KU950 Service Manual page 28

-. 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. Typical
duplexer Tx-band isolation value is 57 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 bands 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.
3.5.3 UMTS Power Amplifier (U103)
The SKY77420, a Wide-band Code Division Multiple Access(WCDMA) Power Amplifier (PA), is a fully
matched 16 -pin surface mount module developed for WCDMA handset applications. This power
amplifier module operates in the 1920-1980MHz band-width. The SKY77420 meets the stringent
WCDMA linearity requirements for output power of up to 28dBm. A low current (VMODE) pin is
provided for high efficiency improvement of the low output power range.
The SKY77420 is manufactured on an advanced InGaP GaAs HBT (Hetero-junction Bipolar
Transistor) MMIC (Microwave Monolithic Integrated Circuit) technology offering state-of-the-art
reliability, temperature stability and ruggedness. The SKY77420 is self contained, incorporating 50ohm
input and output matching networks.
Figure3.5.3-1 UMTS PA functional block diagram
3. TECHNICAL BRIEF
- 29 -