PRODUCT SUMMARY
SKY77555 Tx–Rx FEM Based on CMOS PA for Dual-Band
GSM / GPRS (880–915 MHz and 1710–1785 MHz)
Applications
•
Dual-band cellular handsets
encompassing
-
Class 4 GSM900
-
DCS1800
-
Class 12 GPRS multi-slot
operation
Description
The SKY77555 is a transmit and receive front-end module (FEM) based on CMOS Power Amplifier for
dual-band cellular handsets comprising GSM900 and DCS1800 operation. Designed in a low profile,
compact form factor, the SKY77555 offers a complete Transmit VCO-to-Antenna and Antenna-to-
Receive SAW filter solution. The FEM also supports Class 12 General Packet Radio Service (GPRS)
multi-slot operation.
The module consists of a GSM900/DCS1800 CMOS PA, Tx harmonics filtering, high linearity and low
insertion loss PHEMT RF switches, and diplexer. The CMOS device integrates a full dual-band
GSM/GPRS power amplifier function. High accuracy power control and ramping is achieved on the
CMOS chip via a closed loop power control system. Current drain is limited under load mismatch
conditions via the nature of the innovative power control circuit. The output of the CMOS PA die and
the outputs to the two receive pads are connected to the antenna pad through PHEMT RF switches
and a diplexer. The CMOS die, PHEMT die, and passive components are mounted on a multi-layer
laminate substrate. The assembly is encapsulated with plastic overmold.
Band selection and control of transmit and receive modes are performed using two external control
pads. Refer to the functional block diagram in Figure 1. The band select pad (BS) selects between
GSM and DCS modes of operation. The transmit enable (TxEN) pad controls the receive or transmit
mode of the respective RF switch (Tx = logic 1). Proper timing between transmit enable (TxEN) and
Analog Power Control (VRAMP) allows for high isolation between the antenna and Tx-VCO while the
VCO is being tuned prior to the transmit burst.
The SKY77555 is compatible with logic levels from 1.6 V to 2.8 V for BS and TxEN pads, depending on
the level applied to the VLOGIC pad. This feature provides additional flexibility for the designer in the
selection of FEM interface control logic.
Features
•
Efficiency
-
36% GSM (33.0 dBm)
-
29% DCS (30.5 dBm)
•
Log linear power control
response with <100 dB/V
power control slope
•
Low Rx band noise
•
Supply current
-
1.58 A GSM (33.0 dBm)
-
1.10 A DCS (30.5 dBm)
•
Fully integrated closed loop
•
50
Ω
matched Input/Output
•
Tx–VCO-to-antenna and
antenna-to-Rx-SAW filter
RF interface
•
PHEMT RF switches afford
high linearity, low insertion
loss, and low current in
receive modes
•
Small, low profile package
-
5 mm x 6 mm x 1.05 mm
•
Compatible with multiple
logic families
Figure 1. SKY77555 Functional Block Diagram
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201256A • Skyworks Proprietary and Confidential Information • Products and Product Information are Subject to Change Without Notice. • March 3, 2010
1
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