Author's abstract of master's work
Theme: "Research and Elaboration of Laboratory Technical Means for Study of PLL Systems’ Characteristics in Course of Electric Communication Theory"
Author: Anastasiya Rakitina, master
Donetsk National Technical University
Scientific adviser: Ph.D. Aleksandr Vorontsov, professor
Donetsk National Technical University
e-mail: vag@fcita.dn.ua
Research and Elaboration of Laboratory Technical Means for Study of PLL Systems’ Characteristics in Course of Electric Communication Theory
PLL systems are widely used in communication technology. Proceeding from this they require more attention (time) in TCS (Telecommunication Systems and Networks) specialty curriculum. Especially it concerns laboratory lessons. Moreover, the majority of laboratory researches are based on computer models, which on the whole are ideal and don’t take into account an external factors’ influence a system.
Thus, the goal of the work is model elaboration for laboratory PLL systems researches in course of electric communication theory for training specialists quality improvement.
The key tasks include: substantiation and choice of structural and principle model schemes for PLL systems researches; choice of characteristics for PLL study; PLL experimental researches.
With the purpose of educating it’s reasonable to use a block-diagram of a basic PLL system for phase-locked-loop laboratory researches. It consists of three basic circuits: a phase comparator (PC), a voltage-controlled oscillator (VCO) and a low-pass filter (LPF).
The 74HC/HCT4046A (integrated microscheme) has been taken as a basis of the scheme in this work. This choice is accounted for the fact, that the 74HC/HCT4046A functional packs realize all the basic PLL units and make it possible and easy to construct a complete system. The 74HC/HCT4046A contains: VCO with frequency-determinative elements; input signal forming circuit; three types of phase comparators (that allows to widen studying PLL systems researches).
It’s necessary to chose magnitudes of PLL’s elements to realize the model. Set Ñf=430 pF (such capacitance is acceptable as for the 74HC/HCT4046A load capability and it’s compact). Then Rf=160 Om.
Proceeding from the principles as for components’ values that are given in Data Sheet 74HC/HCT4046A get the next values of the selected components: R1=10 kOm; Ñ1=150 pF; R2=18 kOm.
The elements’ values in the realized PLL system (taking into account their correcting during experiments) are: R1=10 kOm; R2=18 kOm; Rf=160 Om; C1=380 pF; Cf=430 pF.
The 74HC/HCT4046A phase comparators are designated as: «ÐÑ I» – this is an EXCLUSIVE-OR; «ÐÑ II» – this is an edge-triggered phase detector with HIGH level state; «ÐÑ III» – this is an edge-triggered phase detector.
Research tasks for the elaborated PLL system model are: to get the functional dependence fVCOoutput(Uref); to get the magnitudes of phase detectors’ sensitivity (conversion gains); to determine the capture range; to measure jitter in the system; to analyze the got results; to formulate the conclusions.
Under laboratory conditions the spectrum analyzer will be used for jitter measurement (spectrum analyzing method). High-precision instruments are not required for this; and the results are rather clear (graphic).
The PLL system model (with using the 74HC/HCT4046A) practical realization simplicity and its clear nature may be the sufficient grounds for utilizing models like this one in laboratory researches in the course of electric communication theory.