Cmt Rf; Top-Level Description - Nokia RA-2 Rf Description & Troubleshooting

RA-2/3
7 - RF Description and Troubleshooting

CMT RF

Top-level description

The RF module performs the necessary high frequency operations of the GSM850/EGSM900/
1800/1900 tripleband (EDGE) engine. Both the transmitter and receiver have been implement-
ed by using direct conversion architecture which means that the modulator and demodulator
operate at the channel frequency.
The core of the RF is an application-specific integrated circuit, Helgo. Another core component
is a power amplifier module which includes two amplifier chains, one for GSM850/EGSM900
and the other for GSM1800/GSM1900.
Other key components include
• 26 MHz VCTCXO for frequency reference
• 3296-3980 MHz SHF VCO (super high frequency voltage controlled oscillator)
• Antenna switch module (ASM)
• Four SAW filters
The control information for the RF is coming from the baseband section of the engine through
a serial bus, referred later on as RFBus.
The whole RF circuitry is located on one side of the 8-layer PWB.
EMC leakage is prevented by using a metal cans. The RF circuits are separated into two
blocks.
• PA, ASM, LNA, baluns for Rx/Tx and Rx/Tx SAWs.
• Helgo RF IC, VCO + balun, VCTCXO, baluns and EGSM Rx filter
The RF transmission lines constitute of striplines and microstriplines after PA.
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