SKY77527

• High efficiency:
  - GSM850
    38% @ 32.7 dBm
  - GSM900
    38% @ 32.7 dBm
  - DCS1800
    33% @ 30.9 dBm
  - PCS1900
    31% @30.9 dBm
• Low loss PHEMT RF antenna switch
• Detector output: linear V/V
• Small outline: 8 x 6 mm
• Low profile: 1.12 mm Max.
• Low VRAMP current

Tx Front-End Module for Quad-Band GSM / EDGE

The SKY77527-21 Tx Front End Module (FEM) is designed in a compact form factor for quad-bandcellular handsets comprising GSM850/900, DCS1800, PCS1900, supporting GMSK and linear EDGEmodulation. Class 12 General Packet Radio Service (GPRS) multi-slot operation is also supported.

The module SKY77527 consists of a GSM850/900 PA block and a DCS1800/PCS1900 PA block, impedancematchingcircuitry for 50 input and output impedances, a multifunction power amplifier control(MFC) block, low pass harmonic rejection filters, and an SP6T Antenna T/R switch.

Two separate Heterojunction Bipolar Transistor (HBT) PA blocks of SKY77527 are fabricated onto an InGaP die; onesupports the GSM850/900 bands, the other supports the DCS1800/PCS1900 bands. The InGaP PAdie, the silicon MFC die, PHEMT switch die, and the passive components are mounted on a multi-layerlaminate substrate. The assembly of SKY77527 is encapsulated with plastic overmold.

Band select (BS1 and BS2) circuitry of SKY77527 is used to select the desired Tx and Rx frequency bands; MODEcircuitry selects GMSK modulation (logic 0) or EDGE modulation (logic 1); VRAMP controls the outputpower for GMSK modulation; and VBIAS provides bias optimization for EDGE and GMSK modulationdepending on the state of MODE control.

The Multi-function Control (MFC) of SKY77527 provides "pinout" for interoperation with an external power controlloop. The external circuit uses the Linear Detector output to provide closed loop power control in bothEDGE and GMSK modes of operation. The power control loop together with the MFC will reducesensitivity to antenna load, input drive, temperature, power supply, and process variation. The combined circuit of SKY77527 configures the PA for fixed gain in 8PSK mode while providing the ability to optimizethe PA bias at different power levels to maximize efficiency.