Modulasi sudut 2
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Modulasi Sudut (2). Levy Olivia MT. 3.3.3 Implementation of Angle Modulators and Demodulators. Design an oscillator whose frequency changes with the input voltage. Voltage-controlled oscillator Varactor diode - capacitance changed with the applied voltage.

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Modulasi sudut 2

Modulasi Sudut (2)

Levy Olivia MT


Modulasi sudut 2

3.3.3 Implementation of Angle Modulators and Demodulators

  • Design an oscillator whose frequency changes with the input voltage.

  • Voltage-controlled oscillator

    • Varactor diode - capacitance changed with the applied voltage.

    • A inductor with the varactor diode is used in the oscillator circuit.


Modulasi sudut 2

  • Let the capacitance of the varactor diode is given by

  • When m(t) = 0, the frequency of the tuned circuit is given by

  • In general for nonzero m(t), we have

  • Assuming that

  • We have


Modulasi sudut 2

  • Indirect method for generation of FM and PM signals

    • generate a narrow band angle-modulated signal

    • change the narrow band signal to wideband signal


Modulasi sudut 2

  • Generate wideband angle-modulated signals from narrow band angle-modulated signals

    • frequency multiplier

    • implemented by nonlinear device and bandpass filters

  • Using down converter


Modulasi sudut 2

  • A nonlinear device followed by a bandpass filter tuned to the desired center frequency can be used as frequency multiplier.

  • For example, assume a nonlinear device has the function

  • The output signal will be

  • The frequency is multiplied by a factor of 2.


Modulasi sudut 2

  • FM demodulation

    • generate an AM signal

    • use AM demodulator to recover the message signal

  • Pass the FM signal through a filter with response

  • If the input to the system is

  • the output

  • The above signal is an AM signal.


Modulasi sudut 2

FM to AM converter: Tuned circuit implementation

But, usually the linear region of the frequency characteristic may not be wide enough.


Modulasi sudut 2

  • Balanced discriminator

    • use two tuned circuits

    • connect in series to form a linear frequency response region.


Modulasi sudut 2

  • FM demodulator with feedback


Modulasi sudut 2

  • FM demodulator with phase-locked loop (PLL)

  • Input :

  • VCO output:

  • Phase Comparator:


Modulasi sudut 2

  • Linearized model of the PLL

  • or


Modulasi sudut 2

  • By taking the Fourier transform

  • Suppose that we design G(f) such that

v(t) is the demodulated signal


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