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

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

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

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

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.

use AM demodulator to recover the message signal 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.

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

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

FM demodulator with feedback

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

Linearized model of the PLL or

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