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Modulasi Sudut (2)

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)

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  1. Modulasi Sudut (2) Levy Olivia MT

  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.

  3. 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

  4. Indirect method for generation of FM and PM signals • generate a narrow band angle-modulated signal • change the narrow band signal to wideband signal

  5. Generate wideband angle-modulated signals from narrow band angle-modulated signals • frequency multiplier • implemented by nonlinear device and bandpass filters • Using down converter

  6. 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.

  7. 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.

  8. FM to AM converter: Tuned circuit implementation But, usually the linear region of the frequency characteristic may not be wide enough.

  9. Balanced discriminator • use two tuned circuits • connect in series to form a linear frequency response region.

  10. FM demodulator with feedback

  11. FM demodulator with phase-locked loop (PLL) • Input : • VCO output: • Phase Comparator:

  12. Linearized model of the PLL • or

  13. By taking the Fourier transform • Suppose that we design G(f) such that v(t) is the demodulated signal

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