SKY77528

• High efficiency:
  - GSM850, 45% (peak)
  - EGSM900, 45% (peak)
  - DCS1800, 40% (peak)
  - PCS1900, 40% (peak)
• Low-loss PHEMT RF antenna switch
• Detector output: linear dB/V
• Closed loop GMSK mode power control
• Low VRAMP current
• Low VBATT detection
• Integrated temperature sensor
• Small Package - 8 mm x 6 mm
• Low Profile - 1.1 mm Max.

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

The SKY77528 is a transmit Front-End Module (FEM) designed for quad-band Global System forMobile Communications (GSM), General Packet Radio Service (GPRS), and Enhanced Data Rate forGSM Evolution (EDGE) handsets and modules.

The SKY77528 consists of a GSM850/EGSM900 PA block and a DCS1800/PCS1900 PA block,impedance-matching circuitry for 50 inputs and outputs, a multi-function PA control block, lowpassharmonic rejection filter, and a transmit/receive antenna switch.

Two Heterojunction Bipolar Transistor (HBT) PA blocks of SKY77528 are fabricated onto an Indium GalliumPhosphide (InGaP) die; one block supports the GSM850 and EGSM900 bands, the other supports theDCS1800 and PCS1900 bands. The InGaP die, the Silicon (Si) die, the PHEMT die, and the passivecomponents are mounted on a multi-layer laminate substrate. The entire assembly of SKY77528 is encapsulatedwith plastic overmold.

Pad signals BS1 and BS2 of SKY77528 select the GSM/EGSM or DCS/PCS frequency bands. The TX_EN pad signalselects transmit or receive mode of the respective RF switch. MODE pad circuitry selects GMSKmodulation or EDGE modulation. The VRAMP pad of SKY77528 controls the output power for GMSK modulation andprovides bias optimization for EDGE modulation depending on the state of the MODE pad.

An integrated Multi-Function Control (MFC) circuit of SKY77528 provides closed loop power control in GMSK mode,reducing sensitivity to antenna load, input drive, temperature, power supply, and process variation. InEDGE mode, the MFC configures the PA for fixed gain and provides the ability to optimize the PA biasoperation at different power levels. The VDET pad of SKY77528 is used to detect saturation conditions in GMSKmode (which automatically reduces the VRAMP output) and for power control in EDGE mode.