Nokia RM-132 Service Manual & Parts Manual

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Nokia RM-132 Service Manual & Parts Manual Manual pdf 335 page image

The filter is followed by an AGC amplifier with adjustable gain. The signal is further amplified before it is fedto balanced analog IQ output pins. Analogue output pins are accompanied by reference voltage output, whichsets the DC level for the AD converter in BB ASIC.GSM receiverAs GSM Rx branches are functionally identical, the following description is applicable to all of them.The received signal goes from the GSM antenna to the single feed switch, which routes the received GSMsignal to a front-end module, containing a PIN diode switch matrix. The switch matrix is used for the GSMband as well as for the Rx/Tx selection.The switch matrix is followed by integrated LNA stages in the RF ASIC. The LNAs are followed by demodulatorswhich down-convert the signal to baseband I and Q signals.In the BB-chain there are two adjustable gain stages and one mode specific gain. The first one called BB-gainis just after the demodulator. It has a 12 dB gain range with 6dB steps. After the BB-gain there is the channelselect filter.The main AGC amplifier precedes the channel selection filter. It has 30 dB of gain control range with 3 dBsteps. The final amplifier stage is used as an output buffer for IQ signals. This stage is set to 0 dB gain in theGSM mode.TransmitterIntroduction to transmitter functionalityTransmitter functions are implemented in the RF ASIC N7500.The RF ASICs contain a BB frequency low pass filter, which is tuneable according the signal bandwidth of thesystem in use. In addition, they both contain three separate RF paths (GSM850/900, GSM1800/1900 andWCDMA) comprising of a final frequency IQ modulator and VGA amplifiers.WCDMA transmitterIn the transmitter side, an analogue I/Q modulated signal is fed from the digital baseband into the RF ASICand through the low pass filter. After the filter the signal is fed to the I/Q modulator, which converts thesignal to final TX frequency. There are two separate I/Q modulators, one for WCDMA and another for GSM850/EGSM900 and GSM1800/1900 signals. The WCDMA branch is selected by biasing the appropriate modulator.The modulator is followed by two VGA stages. The signal then exits the RF ASIC via a balanced line. The signalis band pass filtered by a SAW filter before it is fed to WCDMA PA module.After the PA, the transmitted WCDMA signal is fed through the duplex filter to the single feed antenna switchand then to the antenna.WCDMA power controlWCDMA TX power control is performed by the two VGA stages in the RF ASIC.The gain of VGA amplifier chain is controlled by a DA converter in BB. The same DA converter is shared by GSMTX power control function.WCDMA PA moduleWCDMA PA is housed in a separate module having a variable supply voltage input for the amplifier stages(Vcc11), a battery supply voltage for the bias circuits (Vcc12) and one bias current input. Bias current isgenerated by 5 bit DA (DAC201) converter in RF ASIC N7500. The converter is controlled via RFBus.In production the PA quiescent current can be tuned to target value by adjusting the bias current of PA outputstage. The bias current is also used as PA on/off controls.RM-132; RM-133System Module Nokia Customer CareIssue 1 COMPANY CONFIDENTIAL Page 9 –37Copyright © 2006 Nokia. All rights reserved.