1. Urgency of a problem.

In process of occurrence and development of new technologies the problem with stability of carrier frequency of send/receive devices becomes more and more actual. As frequencies of passing devices reach already several hundreds GHz also maintenance of communication on such frequency assumes production of more rigid requirements to characteristics of a signal.

2. The purposes and research problems.

Object of designing – the generator of carrier fluctuation for the MICROWAVE of a radio channel with a low level of phase noise.

The purpose of work – research of influence noise characteristics of oscillators on jitter and designing of the highly stable generator of carrier fluctuation for the MICROWAVE of a wave band.

Scope – networks of reception / data transfer.

Results of work – experimental confirmations and substantiations of a choice of structure and element base for creation of the highly stable generator of carrier fluctuation.

3. Brief theoretical data.

3.1. The reasons of occurrence jitter.

Transition to new technologies of communication, has called great variety of the problems closely connected to principles of signaling both in analog, and in a digital kind. One of problems which arise at signaling, is instability of frequency (and, hence, and phases) the transferred (accepted) signal. This concept has received the name jitter or phase noise. There are some principal causes of occurrence jitter , that influence parameters of quality of communication systems. In particular, occurrence in system regular and irregular jitter is caused by the different reasons of its occurrence. Basically, the reason of occurrence jitter can be infringements in the channel of transfer or electromagnetic handicapes and an interference with external sources of a signal, such as noise, reflections, cross handicapes or an interference with circuits of a current voltage and other sources of magnetic noise. But nevertheless one of principal causes of occurrence jitter in a radio channel is instability of the quartz generator and carrier frequency. And instability of an initial signal directly depends on characteristics of quartz and from the circuit in which he is switched on. Instability of quartz is only one side of a problem. The signal from the generator acts on a chain of multipliers which increases frequency up to necessary for transfer on a liaison channel. And since from the generator the signal not with an ideal spectrum (i.e. is present noise "pedestal") simultaneously with multiplication of frequency of a useful signal the handicap is multiplied also leaves, and the ratio signal/noise considerably worsens.

3.2. Quartz resonators.

Piezoelectric resonators ( PR ) are passive components of radio-electronic equipment ( REE ) and are intended for use in analog circuits for stabilization and allocation of electric fluctuations of the certain frequency or a strip of frequencies. In wide area of frequencies resistance PR has capacitor character and only on some frequencies has sharply expressed resonance that determines the name of a component.

The basic electric parameter PR is the frequency of its resonance rigidly fixed. Any devices for its change PR usually has no.

Selective, resonant character of resistance PR determines areas of their application — circuits of frequency selection of various radio engineering devices, mainly generators of electric fluctuations of high stability of frequency and frequency filters of the big selectivity.

The range of frequencies quartz resonators is rather wide. Beginning in the field of sound frequencies from several hundreds hertz, he reaches without interruption up to frequencies of the MICROWAVE and has reached already 500...1000MHz.

For piezoceramic resonators the range of frequencies in the top part is limited to frequencies 10...20MHz, that is determined by non-uniform polycrystalline structure of a ceramic piezoelectric material. Resonators from new piezocrystals block a little bit others ranges of frequencies, sometimes narrower, that speaks, on the one hand, other elastic properties and crystal symmetry, and with another — their smaller level of scrutiny.

Fluctuations of resonators are accompanied a different sort by losses which set determines values of the dynamic resistance named therefore sometimes resistance of losses, hence, and good quality. These losses have both mechanical, and the electric nature. Quartz is almost ideal dielectric, therefore losses of a dielectric origin can not be considered.

4. The brief characteristic of object of researches.

In VCO for VHF of a range the quartz resonator usually works on frequency about 100MHz which then increases up to required. It is a critical case as this generator has very low шумовой a threshold, and each stage of multiplication adds noise in 6dB to a signal with each doubling frequency. Besides the technology of multiplication of frequency is connected to losses; the level of a signal decreases more strongly with increase about multiplication, and the noise inherent in amplifiers of the first cascades can reduce a threshold even faster. Multiplying frequency of quartz with 100MHz up to 10GHz, the noise level increases on 40dB. And on 250GHz the added noise would be 68dB or more.

Generation directed on final frequency usually consider impractical for the lack of corresponding high-frequency crystals. Therefore the quartz generator with on the following multiplication (fig. 3.1) - a comprehensible method of achievement of final frequency.

Fig. 4.1. An example of a chain of multiplication on 1944MHz.

The frequency of quartz chosen for start of a chain, it will be obvious to depend on necessary final frequency. If it is too low initial frequency then the high order of multiplication will be necessary that can call problems with stability is chosen. It can complicate also maintenance of sufficient kill between stages to reduce a level of undesirable handicapes on an output. Because of too high frequency of quartz crystals become very expensive and fragile. Optimum initial frequency for many amateur microwave devices is in a range 90-130MHz.

Quartz generators which work in a range 100MHz, use the crystals raised on the fifth or seventh harmonic. There is a set of corresponding circuits of generators, but owing to difficult reproducibility, low stability and noise characteristics, the choice stops only on the some people. Most known of them - quartz generators on Colpitz crystals that powerful field transistors and active elements use.

5. The received results and the further directions of researches

Modeling the generator and the subsequent chain of multiplication, experiments have been carried out and the following results are received.

5.1. Experiment 1. Modelling noise properties of cascades of multiplication.

The purpose: carry out modelling the transmitter for the MICROWAVE which will consist of the generator of carrier fluctuation on the quartz resonator and a consecutive chain of cascades of multiplication (trebling) of frequency and with the help of model to investigate influence of own noise of the circuit on a spectrum of a signal, in particular, on ratio Рs/Рn on an output of the device. Research of influence of noise is spent for each cascade separately. To find optimum value Ku at which the best ratio Ps/Pn will be provided. To determine, what from cascades brings the greatest handicapes; what element base of the cascade should pay the greatest attention at designing transmitters for the MICROWAVE.

The order of performance: increasing Ku each cascade in a range from 10 up to 100 to determine the best ratio Ps/Pn , thus submitting noise (U=0,005…0,05V) all over again on everything, then on last 2 and, eventually, on last cascade.

Structure of the circuit of experiment (fig. 5.1):

Fig. 5.1. The circuit of experiment

1 (the block 0) – the generator of sine wave fluctuation on the quartz resonator, adjusted to frequency 121,5MHz.

2 (blocks 1,2,6,3,4) – the cascade of trebling of frequency:

• the noise brought by 1st cascade;
• the amplifier of a signal (Ku=10... 100);
• the terminator of a signal (fig. 5.2). Its form can be changed (for allocation of other harmonics), changing factors at x in blocks 3, 8, 12;
• the strip filter which allocates 3d harmonic (364,5MHz).

Fig. 5.2. The form of function of the terminator

3 (blocks 18,16,7,8,9) – the cascade of trebling of frequency:

• the noise brought by 2nd cascade;
• the amplifier of a signal (Ku=10... 100);
• the terminator of a signal;
• the strip filter which allocates 9 harmonic (1093,5MHz).

4 (blocks 19,17,11,12,13) – the cascade of trebling of frequency:

• the noise brought by 3d cascade;
• the amplifier of a signal (Ku=10... 100);
• the terminator of a signal;
• the strip filter which allocates 27 harmonic (3280,5MHz).

Conclusions on 1 experiment:

1 - noise on 1, 2 and 3 cascade.

Character dependences (fig. 5.3) Ps/Pn(Ku) nonlinear also has the big number of maxima and minima. Such quantity of extrema is called by the form of function of terminators (fig. 5.2). But all the same the global minimum is observed at Ku=14, Ps/Pn=11dB. Maxima it is possible to allocate a little: the first is observed at Ku=11, and the second – at Ku=25. From here it is possible to draw a conclusion, that to choice Ku the special approach as the factor is elected "blindly" can to give small ratio Ps/Pn that will have an effect on the following cascades of multiplication is necessary.

Fig. 5.3. Dependence Ps/Pn ( Ku )

2 - noise on 2 and 3 cascade.

Character dependences (fig. 7.4) Ps/Pn (Ku) also nonlinear and as maxima it is possible to allocate a range of values Ku=20..100 (here Ps/Pn>48dB). A minimum outstanding also at Ku=13.

Fig. 5.4. Dependence Ps/Pn(Ku)

3 - noise on 3-rd cascade.

Character dependences (fig. 5.5) Ps/Pn(Ku) similar to the previous research. The minimum is seen at Ku=13, and the maximum lays in range Ku=15…100.

Fig. 5.5. Dependence Ps/Pn(Ku)

Seeing results, it is possible to say, that maximal ratio Ps/Pn is provided at Ku=20.. 100 on each of cascades of multiplication. Also from dependences it is visible, that noise on the first cascade most influences a spectrum of a signal. From here follows, that at creation of the circuit of the first cascade of multiplication, it is necessary to put strict requirements to a choice of element base, to own noise of elements (for example, transistors).

5.2. Experiment 2. Modelling noise properties of filters.

The purpose: to carry out modelling the transmitter for the MICROWAVE which will consist of the generator of carrier fluctuation on the quartz resonator and a consecutive chain of cascades of multiplication (trebling) of frequency and with the help of model to investigate influence of good quality (Q = f/df) filters on a spectrum of a signal, in particular, on ratio Ps/Pn on output of the device. Research of influence of noise is spent for each cascade separately. To find optimum value Q at which the best ratio Ps/Pn will be provided. To determine, what filter of the cascade should pay the greatest attention at designing transmitters for the MICROWAVE.

The order of performance: increasing Q filters of each cascade in a range from 10 up to 100 to determine the best ratio Ps/Pn , thus changing good quality of each filter separately.

Structure of the circuit of experiment (fig. 5.6).

Fig. 5.6. The circuit of experiment

Conclusions on 2 experiment:

1. Increase in good quality of 1st filter (the block 4).

Character dependences (fig. 5.7) Ps/Pn(Q) almost linear and ratio Ps/Pn worsens in process of increase in good quality. Such character of dependence is called by nonlinearity of the filter. Direct dependence Ps/Pn(Q) would be logical, but all has left on the contrary. Therefore this effect needs to be investigated in more details in the future experiments. Under the schedule it is visible, that good quality of 1st filter should be taken in range Q=10-25.

Fig. 5.7. Dependence Ps/Pn(Q)

2. Increase in good quality of 2nd filter (the block 9).

Character dependences (fig. 5.8) Ps/Pn(Q) almost linear and ratio Ps/Pn grows in process of increase in good quality a little.

Fig. 5.8. Dependence Ps/Pn(Q)

3. Increase in good quality of 3d filter (the block 13).

Character dependences (fig. 5.9) Ps/Pn(Q) linear and ratio Ps/Pn remains constant in process of increase in good quality.

Fig. 5.9. Dependence Ps/Pn(Q)

It is possible to say, that changes of good quality influence only ratio Ps/Pn after the filter of 1st cascade of multiplication. From here follows, that at creation of the circuit of the first cascade of multiplication, it is necessary to put strict requirements to a choice of good quality of the filter.

The analysis of results.

On the basis of the carried out researches it is possible to determine such recommendations concerning designing frequency multipliers:

• to start quartzes on that harmonic to which he is adjusted;

• to reduce phase noise at the expense of a choice of the qualitative circuit and element base with a low level of noise;

• for achievement of final frequency to use the quartz generator with the subsequent multiplication;

• initial multiplication of frequency should be made on small number for minimization of handicapes;

• for circuits of multiplication it is necessary to choose such factor of amplification, at which ratio signal/noise maximum;

• good quality of the filter after the first cascade of multiplication should be taken such which would provide an optimum ratio signal/noise.