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. 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

5. 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

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. 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.

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

9. 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.

11. FM demodulator with feedback

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

13. Linearized model of the PLLor

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