Describe working of frequency synthesizer used in mobile handset. OR Draw block diagram of frequency synthesizer unit of mobile handset and state its function in cellular handset.


Draw neat block diagram of frequency synthesizer and label the blocks. Explain its working.

1 Answer

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1) The synthesizer is used for developing all the signals used by the transmitter and Receiver.

2) It uses PLL circuits and mixer.

3) The crystal oscillator provides a reference for two PLL.

4) The function of PLL is to lock or synchronize frequency of VCO to that of input signal.

5) The output of VCO 2 is used as local oscillator frequency for the first mixer in the oscillator

6) The output of the two VCO are mixed together to produce the transmitter output frequency.

7) The frequency divider block receive divide by number from the logic section. These numbers are given by MTSO computer.

8) The divide by number will set Transmit and receive channel frequencies.

9) The two output produced by frequency synthesizer are applied to the modulator box in the transmitter and the first mixer in receiver respectively.

10) The frequency synthesizer thus act as local oscillator which can produce a wide range of frequencies with high stability

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