Only For Training And Service Purposes - LG KP330 Service Manual

3.6.7 UMTS Diversity Rx RF filter
The diversity receiver path does not require a duplexer to separate Rx and Tx signals, but
must include an Rx filter before the first gain stage to achieve performance comparable to the
Rx-path within a duplexer. In the UMTS paths the first gain stage is at the RTR6285 input.
Key performance requirements of the first bandpass filter include:
Insertion loss – this component is positioned before the first gain stage, so its loss degrades
■
receiver noise figure (sensitivity) directly. Insertion loss is most critical here!
Out-of-band rejection or attenuation – this filter provides input selectivity for the receiver and
■
suppresses transmitter leakage. Rejection levels are specified over a number of frequency
ranges (see device data sheets for representative values).
Tx-band leakage – the transmitter channel power combines with Rx-band jammers to create
□
cross-modulation within the LNA or pre-LNA that falls in-band and corrupts receiver
performance. Furthermore, the secondary UMTS chains have low operating points and might
be driven into compression if sufficient suppression is not achieved. The RF filter must provide
rejection of this Tx-band leakage.
Other frequencies of particular concern – bands known to include other wireless transmitters
□
that may deliver significant power levels to the receiver input.
Of course, passband ripple and return loss are still important in all cases for the same reasons
explained in the duplexer section. This Rx input filter has a single-ended configuration at its
input and output.
Copyright © 2008 LG Electronics. Inc. All right reserved.

Only for training and service purposes

KP330 Operational Description
- 45 -
3. TECHNICAL BRIEF
LGE Internal Use Only