Off-Chip Rf Components - LG U300 Service Manual

The off-chip loop filter allows optimization of key PLL performance characteristics (stability, transitory
response, settling time, and phase noise) for different applications. Guidelines are provided in the next
subsection for proper implementation of this critical circuit.

3.5 Off-chip RF Components

3.5.1 Antenna Switch Module(U100)
The CXG1190AEQ is one of a range of low insertion loss, high power MMIC antenna switches for
GSM/UMTS dual-mode handset. The low insertion loss serves to extend the handset talk time.
The switch also contains on-chip logic circuits and built-in dual-LPF on GSM transmit paths for
suppression of transmitter harmonics. The dual-LPF is mounted on the lead frame and enables the
reduction of component count and simple PCB layout.
(Applications: GSM (Triple/Quad band)/UMTS dual-mode handset)
3.5.2 UMTS duplexer (FL104)
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 U300 typical losses:
UMTS Tx = 1.3 dB, UMTS Rx = 1.7 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. Typical duplexer Rx band isolation value is 44 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. Typical
duplexer Tx-band isolation value is 64 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 <2.3:1).
3. TECHNICAL BRIEF
- 29 -