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Research Report

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  • ST2132

    Scientech Technologies Pvt. Ltd. 17

    Introduction to Mobile Section

    Description of block diagram:For understanding the basic circuit of any mobile phone it can be divided in followingthree sections:A. Receiving SectionB. Transmitting SectionC. Base band Control/UI Section

    Receiver SectionA. Receiver Section:The receiver is direct conversion dual band linear receive. When any call is receivedin mobile phone, the receiving signal comes at antenna first, which is of loop typethen to pin no.4 of antenna switch (Diplexer) (Z502) through capacitor C593. Thisantenna switch makes function of switching of receiving, transmitting, GSM andDCS frequency band. Switching signals is given at its control pins from CPU for it,GSM-RX signal is made out from pin no.14 of antenna switch, which is given to pinno.7 of Z501 through capacitor C547 receiving signal passes through band pass SAW(Surface acoustic wave) filter (925-960MHz) and is made out from pin 1.Unwanted frequencies coming with GSM frequency bands are filtered by it and onlyrequired band frequencies are passed further. Signal obtained from filter is given toLNA (Low Noise Amplifier) V501. Control voltage is given to amplifier fromHAGAR IC N500; amplification gain of LNA is controlled by it. Because this controlvoltage controls gain of amplifier in automatic way hence considered AGC(Automatic Gain Control). Output level of receiver remains stable by it.Signal obtained from amplifier gain is given to Band Pass SAW filter Z500, signalobtained from pin no.4 of V501 is given to pin no.1 of Z500. Many unwantedfrequencies are amplified with the amplification receiving signals. It is very essentialto separate these frequencies, otherwise further these frequencies can become reasonof noise. Band Pass Filter Z500 makes this function; signal is made out from its oneoutput pin no.7 and given to balancing transformer T501. The balancing transformersmake balancing from single ended receiving signal. Signal is made balance bytransformer T501 and comes at pin no.C9 and B9 of IC N500, which are input pins ofGSM-RX of N500 RF IC (HAGAR IC).Mixing and Demodulation (conversion to LF) operation of receiving signal is made inHAGAR IC N500. Oscillation signal produced by VCO (Voltage ControlledOscillator) G500 is mixed in these signals for this operation. This VCO (VoltageControlled Oscillator) G500 produces separate local oscillation signals in GSM andDCS frequency band. VCO produces 3700-3840 MHz for GSM and 3610-3760 MHzfor DCS 1800. This signal is given to pin no. J2 and J5 of IC N500 through signaltransformer T502, this signal is amplified in IC. It is divided by four, for GSM (localoscillation signal of 935 to 960 MHz) is obtained and by 2 for DCS 1800 PLL anddividers are in HAGAR IC. GSM receiving signal is mixed in this signal, after that it

  • ST2132

    Scientech Technologies Pvt. Ltd. 18

    is filtered and given to demodulator and made I/Q signal. This receiving I/Q signal ismade out from pin numberG5 and G6 of IF IC N500 which can be viewed at (3) and(4), which is given to audio signal COBBA IC N100.Demodulation is completed digital to analog conversion and audio frequencyamplification etc functions are made in it. It also makes functions as interface forcompleting control functions of AFC, PAC and AGC etc CPU D300 has full controlof all functions of this IC. Audio frequency signal is obtained in this IC through aPCM signal. This is amplified by audio frequency amplifier. This audio frequencysignal is obtained from pin no.D1 and D2 of COBBA IC N100, it is given to speakerand sound is obtained.

    Transmitter SectionB. Transmitter Section:At the time of transmitting microphone converts voice signal in to electric signal.This signal is given to pin no. A3 & B3 of audio frequency processing IC N100.Transistor V101 connected from pin no.D6 of this IC is a mic power supply controllertransistor. This transistor provides control voltage to microphone signal given bymicrophone is at first amplified in COBBA IC N100. After that it is made PCM codeand digital signal is obtained, this signal is sent to central processing unit D300 forvoice coding and channel coding at that place data stream is made which is sent backto audio processing IC N100 for GMSK modulation. In this way A/D conversion,coding, Encryption channel coding and modulation etc functions are made in COBBAIC and CPU. I/Q signals are serially transmitted from COBBA IC and given totransmitting modulation process in HAGAR IC N500 which can measured at (5) and(6).VCO signals are mixed with TX-IQ signal in HAGAR IC N500. These localoscillation signals are produced by local oscillation modules G-500, VCO moduleG500 generates local oscillation signals of two different values. Oscillation signals3520 to 3660 MHz in condition of GSM 900 frequency band, which is divided byfour, 890 to 915 MHz is obtained and mixed with transmitting I, Q (TX-1, Q) signal.Signal output level at this stage is 5dBm Working system of VCO module G500 iscontrolled by PLL circuit made in HAGAR IC N500.After the modulation, Tx signal is converted to single ended by balance circuit(mutual coupler) and after filtering in 2500 (880915Hz) the signal is amplified bypre-amplifier circuit and buffered out the final amplification is realized with dualband power amplifier. It has a gain control, which is controlled with a power controlloop in HAGAR IC. Power amplifier produces a signal over 2W in GSM band. Gaincontrol range is over 35dBm.Now this signal is given to Dual band directional coupler connected between PA andAntenna switch, Directional coupler take a sample from the forward going powerwith certain ratio. This detected voltage is compared in error amplifier in HAGAR ICto a Tx voltage generated by COBBA IC. Then the signal is given to Antenna switchand the signal is transmitted through antenna, the signal is of +33dBm approximately.Note: Before performing the observation, fully charged the battery and keep thecharging On.

  • ST2132

    Scientech Technologies Pvt. Ltd. 76

    Component Layout(For Information Only)

    Figure 31