Rf Module Description - Nokia RH-37 Series Manual

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RF Module Description

The RF module performs the necessary high frequency operations of the triple-band
engine. Both the transmitter and receiver have been implemented by using a direct con-
version architecture, which means that the modulator and demodulator operate on the
channel frequency. No intermediate frequencies are used for up- or down-conversion.
The core of the RF is an application-specific integrated circuit (RF ASIC), Helgo85. The
other RF key components are:
• An EDGE capable power amplifier module, which includes two amplifier chains,
one for the low band (GSM900) and the other for both high bands (GSM1800
and GSM1900).
• An antenna switch module, which contains filters and switches to combine the
two TX-PA outputs and three Rx chain inputs to the antenna port.
• 26 MHz reference oscillator (VCTCXO).
• 3296-3980 MHz VCO.
• Three SAW filters for Rx band filtering.
• One SAW filter for the low band (GSM900) Tx path.
The control information for the RF is coming from the baseband section of the engine
through a serial bus, referred later on as RFBus. This serial bus is used to pass the infor-
mation on the frequency band, mode of operation, and synthesizer channel for the RF. In
addition, exact timing information and receiver gain settings are transferred through the
RFBus.
Physically, the bus is located between the baseband ASIC called UPP and the RF ASIC.
Using the information obtained from UPP, the RF ASIC controls itself to the required
mode of operation and further sends control signals to the antenna switch and the
power amplifier modules.
In addition to the RFBus, there are still other interface signals for the power control loop
and VCTCXO control and for the modulated waveforms (IQ signals).
The RF circuitry is located in two shielding chambers on one side of the 8 layer PWB con-
taining the following key components: The Small Signal Chamber contains RF ASIC, ref-
erence oscillator (VCTCXO), VCO, and Rx/Tx SAW-filters (GSM900/GSM1800). The Large
Signal Chamber contains the RF Power Amplifier, the Antenna Switch Module, and the
Rx SAW-filter and LNA (GSM1900).
Issue 1 07/04
©Nokia Corporation
RH-37
System Module
Page 47