Spectrum-division frequency modulator

FIELD: radio communications; digital communication systems.

SUBSTANCE: proposed spectrum-division frequency modulator that incorporates provision for using frequency-modulated signals of high modulation index in communication systems where frequency resources are limited has two multipliers, two phase shifters, smoothing-voltage generator, two amplitude-phase modulators, carrier generator, adder, and frequency shift control unit.

EFFECT: enhanced noise immunity of communication systems.

3 cl, 15 dwg

 

The invention relates to the field of radio communications and can be used in digital communication systems, in particular in satellite and terrestrial mobile radio for the formation of FM signals with effective use of the radio spectrum.

Analogues of the claimed devices are frequency modulators using quadrature schemes for the formation of the modulated signal, which include, for example, modulators π/4-DQPSK and CQPSK (Ovchinnikov M.A., Vorob'ev S.V., Sergeev S. Open standards digital trunking radio. Series “Communication in business”, M: ICSTI, LLC “Mobile communications”, 2000, at 166 C. Cm. s and 158). These modulators are made by the same structural schemes (RAS and 8.10). They differ only filters and speed of information transmission (p.160). These modulators include unit conversion, two lowpass filter (filters Nyquist), two of the amplitude modulator and the adder, and two output devices transcoding are connected respectively to the inputs of low-pass filters, the outputs of low-pass filters are connected to the inputs of amplitude modulators, the outputs of these modulators are connected to the inputs of an adder whose output is the output of the frequency modulator. The disadvantage of these frequency modulators is to use only mini the social index frequency-shift keying, that does not allow the dignity of signals with large index modulation.

The closest in technical essence is a modulator performing frequency modulation without breaking phase - Minimum Shift Keying (MSK) or, equivalently, the minimum modulation frequency shift (MMS) (see Banquet V.L., Dorofeev V.M. Digital techniques in satellite communications. - M.: Radio and communication, 1988, - 240 C., Il., p.39-40, risb).

This modulator includes a switch parcel into two channels (even sending one channel, odd in the other), the generator smoothing voltages, two multiplier, a carrier generator, a phase shifter, two amplitude-phase modulator and an adder. Alternate switching parcels input baseband signal into two channels provides a two-fold increase in the duration of parcels in each channel. Smoothing the rectangular parcels of duration 2T0according to the laws of

in each channel, respectively, provides the shape of the envelopes concerns voltages at the outputs of the amplitude and phase modulators corresponding to the shape of the voltage u1and u2. Because this is a smooth (linear) phase change concerns fluctuations in the output of the adder for time T0on +π/2 or -π/2 depending on the make of the input modulating with the persecuted (0 or 1). This phase shift corresponds to the index of the frequency modulation of the output signal m=0,5. This modulator, due to linear phase change over the time of shipment, the absence of phase jumps at the boundaries of the parcels generates a modulated output frequency voltage with compact spectrum. The real spectrum width modulated so signal is 1.18·V, where V is the transmission rate, bit/s used in the modulator MMS Gauss filter gives additional possibilities for reducing the occupied bandwidth (modulation GMSK, see, for example, Ratynski MV Basics of cellular communication/ edited Dbimon. - M.: Radio and communication, 1998. - 248 S., ill., s-126). In addition, in this modulator, there is no direct impact of the modulating signal generator carrier, thus ensuring high stability of the carrier oscillation, and the possibility of rapid change of the carrier frequency, which is important for broadband systems with abrupt frequency change.

However, the requirements for noise immunity and the reception quality is constantly growing, and the ability of the modulator MMS does not meet these requirements, since this modulator provides only the minimum modulation index m=0.5 in.

It is known that if the communication system with an FM demodulator input receiver provided a sufficiently high signal-to-noise ratio, it turns out the tsya advisable to work with large index modulation, because in this mode increase not only the signal level and signal-to-noise ratio at the receiver output, and the gain in the signal-to-noise ratio. This mode is desirable when it is necessary to ensure high quality of transmitted signals. However, the higher the modulation index, the more occupied signal bandwidth, and this fact limits the practical ability to use a large index modulation.

In the invention solves the problem of the formation of the FM signal without breaking phase, the energy spectrum consists of two separate parts, symmetrically located relative to the carrier frequency, the shift in frequency between which is proportional to the index of the frequency manipulation while maintaining their shape; the width of the frequency band occupied by the signal does not change when you change the index of the frequency manipulation.

The technical result is the ability to use FM signals with large index modulation in communication systems with a limited frequency resource, and as a consequence - increased robustness of the communication systems and the quality of the receive signals, the receive gain in signal-to-noise ratio, is proportional to the index of the frequency manipulation.

The solution to this problem is achieved by the frequency modulator, containing two Peremogi the El, two Phaser generator smoothing voltage, two amplitude-phase modulator, the carrier generator and the adder, and the generator output smoothing voltage is connected to the first input of the first multiplier and through the first phase shifter with the first input of the second multiplier, the output of the first multiplier is connected to the first input of the first amplitude-phase modulator, the output of the second multiplier connected to the first input of the second amplitude-phase modulator, the output of carrier generator connected to a second input of the first amplitude-phase modulator and a second phase shifter to the second input of the second amplitude-phase-modulator outputs of the first and second amplitude and phase modulators connected respectively with the first and second inputs of the adder, the output of which is the output of the frequency modulator split spectrum includes the control unit of the frequency shift, the input of which is the input of frequency modulator with the separation of the spectrum, the first output control unit of the frequency shift is connected to the second input of the first multiplier and the second output control unit of the frequency shift is connected to the second input of the second multiplier.

The control unit of the frequency shift contains two elements “Exclusive OR”, two D-flip-flop, four CL the cha and the generator, and the first inputs of the elements of the “Exclusive OR” connected to each other and are the input of the control unit of the frequency shift, the output of the first element of the “Exclusive OR” is connected to the first input of the first D-flip-flop, the output of the second element of the “Exclusive OR” is connected with the first input of the second D-flip-flop, the second inputs of the first and second D-flip-flops are connected respectively with the third and fourth generator output, the first output of the first D-flip-flop is connected to the first input of the first key and the second input of the second element of the “Exclusive OR”, the second output of the first D-flip-flop connected to the first the input of the second key, the first output of the second D-flip-flop is connected to the first input of the third key, the second output of the second D-flip-flop is connected to the first input of the fourth key and the second input of the first element of the “Exclusive OR”, the first and second outputs of the generator are connected respectively to the second input of the first key and the second input of the second key, 5-th and 6-th outputs of the generator are connected respectively to the second input of the third key and the second input of the fourth key, the outputs of the first and second keys are interconnected and form a first output control unit of the frequency shift, the outputs of the third and fourth keys are interconnected and form a second output control unit of frequency is the first shift.

The generator includes a master oscillator, the unit is preset, the frequency divider by two, the frequency divider by 2m (where m is the index of the frequency-shift keying), two of the Johnson counter, two elements Exclusive-OR four differentiating circuit with a limit on the minimum, two driver sawtooth voltage, two elements OR two driver voltage sine wave and the output of the master oscillator is connected with the input of the frequency divider by two, the first output of the frequency divider by two is connected to the first input of the first Johnson counter, the second output of the frequency divider by two is connected to the first input of the frequency divider to 2m, the output of which is connected to the first input of the second Johnson counter, the first output unit PE is connected with the second input of the frequency divider by two, the second output unit PE is connected with the second inputs of the frequency divider on 2m and both counters Johnson, the first output of the first Johnson counter is connected to the first input of the first element of “Exclusive OR”, the second output of the first Johnson counter is connected to the first input of the second element of the “Exclusive OR”, the first output of the second Johnson counter is connected with the second input of the first element of the “Exclusive OR” and to the input of the first differential circuit with a limit on the minimum vtoro the output of the second Johnson counter is connected with the input of the second differentiating circuit, the third output of the second Johnson counter is connected with the second input of the second element of the “Exclusive OR” and to the input of the third differential circuit with a limit on the minimum, the fourth output of the second Johnson counter is connected with the input of the fourth differential circuit with a limit on the minimum, the output of the first element of the “Exclusive OR” is connected with the input of the first driver of the sawtooth voltage, the output of the second element of the “Exclusive OR” is connected with the input of the second driver of the sawtooth voltage, the output of the first driver of the sawtooth voltage is connected with the input of the first driver voltage sine wave output, two outputs which are the first and second outputs of the generator, the output the second driver of the sawtooth voltage is connected with the input of the second driver voltage sine wave output, two outputs which are the fifth and sixth outputs of the generator, the outputs of the first and second differentiating circuit with a limit on the minimum connected with the inputs of the first element OR the output of which is the third generator output, the outputs of the third and fourth differentiating circuit with a limit on the minimum connected with the inputs of the second element OR the output of which is the fourth generator output.

The population is ü signs, characterizing the frequency modulator split spectrum provides the technical result in all cases to which is sought legal protections, and the features related to the control unit of the frequency shift and to the generator, characterize its only in the specific form of execution.

All the essential features of the claimed invention are in causal relationship with achievable technical result. The control unit of the frequency shift converts the input binary packages of the modulating signal in the alternating harmonic voltage 2T0acting on the outputs of this block and the length of the parcels are determined by the equalities:

In these equations m is the index of the frequency-shift keying, which must be ensured;

T0- the duration of the parcels input modulating signal,

t - the current time.

The index of the frequency-shift keying must satisfy the equality m=n is 0.5, where n is a positive integer. The frequency of the voltages u1and u2is mπ/T0. Frequency selection voltages u1and u2provide the required index manipulation. First and second multiplier products smooth envelopes of parcels voltages u1and u2according to the law of sin is odelnoi half-wave, what is needed to reduce the actual width of each part of the spectrum of the output signal and shaping, as in the MSK signal. The voltage outputs of the multiplier products affect the amplitude and phase modulators, in which there is a change of amplitude and phase concerns the vibrations coming from the generator carrier. The addition of these fluctuations gives FM voltage without breaking phase with the modulation index m, which can be set large enough. At m≥1,5 spectrum of this voltage is divided into two halves.

Figure 1 shows the structural diagram of the frequency modulator split spectrum, figure 2 - block diagram of the control unit of the frequency shift in figure 3 - block diagram of the generator, figure 4 - diagram of the oscillator, figure 5 is a block circuit diagram PE, figure 6 - diagram of the frequency divider 2, figure 7 - diagram of the frequency divider on 2m, Fig diagram of the Johnson counter, figure 9 - diagram of a differentiating circuit with a limit on the minimum figure 10 - diagram of the driver of the sawtooth voltage, figure 11 - diagram of the driver voltage is sinusoidal, Fig - temporary diagram of the voltages in the generator, Fig - time diagrams of the voltages in the control unit of the frequency shift, Fig - time diagrams of signals in the frequency modulator split spectrum, Fig - range is supplemented flax characteristic of the output signal of the frequency modulator split spectrum.

Frequency modulator with the division of the spectrum (see figure 1) contains the unit 1 control frequency shift, the first multiplier 2, the first phase shifter 3, and the second multiplier 4, the generator 5 is smoothing the voltage of the first amplitude-phase modulator 6, the second phase shifter 7, the second amplitude-phase modulator 8, the carrier generator 9 and the adder 10, and the input unit 1 controls the frequency shift is the input of frequency modulator with the separation of the spectrum, the first output unit 1 controls the frequency shift is connected to the second input of the first multiplier 2, and the second output is connected with the second input of the second multiplier 4, the output generator 5 smoothing voltage is connected to the first input of the first multiplier 2 and through the first phase shifter 3 to the first input of the second multiplier 4, the output of the first multiplier 2 is connected to the first input of the first amplitude-phase modulator 6, the output of the second multiplier 4 is connected to the first input of the second amplitude-phase modulator 8, the output of the carrier generator 9 is connected with the second input of the first amplitude-phase modulator 6 and through the phase shifter 7 to the second input of the second amplitude-phase modulator 8, the outputs of the amplitude and phase modulators 6 and 8 are connected respectively with the first and second inputs of the adder 10 that one is by the output frequency of the modulator with the division of the spectrum.

The unit 1 control frequency shift (see figure 2) contains the first element 11 “Exclusive OR”, the second element 12 “Exclusive OR”, the first D-flip-flop 13, the second D-flip-flop 14, the first key 15, the second key 16, the third key 17, the fourth key 18 and the generator 19, and the first inputs of the elements 11 and 12 Exclusive OR connected to each other and are input unit 1 controls the frequency shift, the output element 11 “Exclusive OR” is connected to the first input of D-flip-flop 13, the output of element 12 “Exclusive OR is connected to the first input of D-flip-flop 14, the second inputs of D-flip-flops 13 and 14 are connected respectively with the third and the fourth output of the generator 19, the first output of the first D-flip-flop 13 is connected to the first input of the first key 15 and with a second input of the second element 12 “Exclusive OR”, the second output of the first D-flip-flop 13 is connected to the first input of the second key 16, the first output of the second D-flip-flop 14 is connected to the first input of the third key 17, the second output of the second D-flip-flop 14 is connected to the first input of the fourth key 18 and with the second input of the first element 11 “Exclusive OR”, the first and second outputs of the generator 19 are connected respectively to the second input of the first key 15 and the second input of the second key 16, 5-th and 6-th outputs of the generator are connected respectively to the second input of the third key 17 and a second input of the fourth is ljuca 18, the outputs of the keys 15 and 16 are interconnected and form a first output unit 1 controls the frequency shift, the outputs of the keys 17 and 18 are interconnected and form a second output unit 1 control frequency shift.

The generator 19 (see figure 3) contains the master oscillator 20, block 21 preset, the divider 22 frequency by two, the divider 23 frequency on 2m, the first counter 24 Johnson, the second counter 25 Johnson, the first element 26 “Exclusive OR”, the second element 27 “Exclusive OR”, the first differentiating circuit 28 with a limit on the minimum, the second differentiating circuit 29 with a limit on the minimum, a third differentiating circuit 30 with a limit on the minimum, fourth differentiating circuit 31 with a limit on the minimum, the first imaging unit 32 of the sawtooth voltage, the second imaging unit 33 voltage sawtooth form, the first element 34 OR the second element 35 OR the first shaper 36 voltage sine wave and the second imaging unit 37 of the voltage sine wave, and the output of oscillator 20 is connected with the input of the divider 22 frequency by two, the first output of the divider 22 frequency on two connected to the first input of the first counter 24 Johnson, the second output of the divider 22 frequency on two connected with the first input of the divider 23 frequency on 2m, the output of which is connected with the first input of the second counter 2 Johnson, the first output unit 21 PE is connected with the second input of the divider 22 frequency by two, the second output unit 21 PE is connected with the second inputs of the frequency divider 23 on 2m and counters 24 and 25 Johnson, the first output of the first counter 24 Johnson connects with the first input of the first element 26 “Exclusive OR”, the second output of the first counter 24 Johnson connects with the first input of the second element 27 “Exclusive OR”, the first output of the second counter 25 Johnson connects with the second input of the first element 26 “Exclusive OR” and to the input of the first differentiating circuit 28 with a limit on the minimum the second output of the second counter 25 Johnson connected with the input of the second differentiating circuit 29, the third output of the second counter 25 Johnson connects with the second input of the second element 27 “Exclusive OR” and to the input of the third differential circuit 30 with a limit on the minimum, the fourth output of the second counter 25 Johnson connected with the input of the fourth differential circuit 31 with a limit on the minimum, the output of the first element 26 “Exclusive OR” is connected with the input of the first driver 32 of the sawtooth voltage, the output of the second element 27 “Exclusive OR” is connected with the input of the second imaging unit 33 of the sawtooth voltage, the output of the first shaper 32 sawtooth voltage which forms is connected with the input of the first driver 36 of the voltage sine wave, two outputs which are the first and second outputs of the generator 19, the output of the second imaging unit 33 of the sawtooth voltage is connected with the input of the second imaging unit 37 of the voltage sine wave output, two outputs which are the fifth and sixth outputs of the generator 19, the outputs of the first and second differentiating circuits 28 and 29 with the restriction on the minimum connected with the inputs of the first element 34 OR the output of which is the third output of the generator 19, the outputs of the third and fourth differential circuits 30 and 31 with a limit on the minimum connected with the inputs of the second element 35 OR the output of which is the fourth output of the generator 19.

In the unit 1 control frequency shift (see figure 2) interconnected first inputs of the elements 11 and 12 of the “Exclusive OR” are the input of frequency modulator to which is fed the input of the modulating binary signal. The outputs of the keys 15 and 16, connected together, are the first output of the unit 1 control frequency shift, which is connected with the second input of the first multiplier 2. The outputs of the keys 17 and 18, connected together, are the second output unit 1 controls the frequency shift, which is connected with the second input of the second multiplier 4. The six outputs of the generator 19 are connected to the inputs of functional units unit 1 controls the frequency change is om. The first output driver 36 of the voltage sine wave is connected with the second input key 15, the second output driver 36 sine wave is connected with the second input key 16, the first output driver 37 of the voltage sine wave is connected with the second input key 18, the second output driver 37 of the voltage sine wave is connected with the second input key 17, the output element 34 OR is connected with the second input of D-flip-flop 13, the output element 35 OR connected with a second input of D-flip-flop 14.

Most of the functional units of the frequency modulator split spectrum run on IMS: items 11, 12, 26, and 27 “Exclusive OR” - CLP, D-flip 13 and 14 KR1533TM2, the keys 15...18 - KRKN oscillator 20 - CRG scheme 4, block 21 presets can be performed according to scheme 5 transistors CTG, the divider 22 frequency of two can be performed on RSD-triggers CTM according to scheme 6. The frequency divider by 2m (where m is the required index frequency modulation) can be made according to the scheme shown in RIS-in the book: Veniaminov, VN, Lebedev, O., Miroshnichenko A.I. Chips and their application: Help, aid. - 3rd ed., added and extra - M.: Radio and communication, 1989. 240 C., Il. For the case of m=5.5 diagram of the frequency divider on 2m presented on Fig.7; included in this schema elements are performed on the IC 4-bit counter CC2 - KIA, 3-input accumulating element AND CLI, RS-trigger - CTR. Schemes and these are the elements presented in the book: Shyla V.L. Popular digital circuits: the manual. 2.-ed., Corr. - Chelyabinsk: metallurgy, Chelyabinsk div., 1989. - 352 S.: ill. on RIS (p.40), RIS (s) and RIS (p.88). The Johnson counter is performed on the basis of the shift register with a cross-link. The principle of operation of these counters, and a scheme based on the 5-bit register is presented on p.134 and is above books Benjamin NR. and other Scheme of the Johnson counter based on the 2-bit counter, which is used in the frequency modulator with m=5,5 presented on Fig. In the Johnson counter 24 output signals are taken from the outputs Q1and Q2and in the Johnson counter 25 with outputs Q1, Q2, Q3and Q4. The differentiating circuit 28...31 with a limit on the minimum can be performed on RC circuits with elements AND CLI restrict to a minimum, eliminate the negative pulses at the outputs of the differentiating circuits (Fig.9). Two elements 34 and 35 OR CRL. Diagram of the driver of the sawtooth voltage (PNP) is shown in figure 10; this device runs on an integrating RC circuit with a buffer amplifier operational amplifier, for example, CRUD. Driver voltage sine wave (FTS) is performed on the basis of the schemes is, presented in the book: Earl R. Electronic circuits: 1300 examples: TRANS. from English. - M.: Mir, 1989, 688 S., ill., s. The shaper circuit voltage sine wave figure 11 presents; with the outputs of the amplifiers included in the shaper, removable direct and inverted signals (S1and S3or S2and S4).

The operation of the frequency modulator split spectrum is as follows. The generator 19 (Fig 3) generates four sequence segments of a sine wave of frequency mπ/T0with a mutual phase shift π/4 and two sequences of clock pulses, a certain way fazirovannykh on these segments of the sinusoid. Timing diagrams of signals in the generator 19 presents on Fig. The diagrams are presented for the case when the index is frequency-shift keying m=5,5. The master oscillator 20 generates a signal in the form of a square wave, the frequency of which is connected with a duration of T0parcels of the modulating signal ratio: fg=4m/T0. From this signal, the divider 22 frequency on two forms meander frequency f:2=2m/T0. The shape of this voltage is shown in Fig (u22). The divider 23 frequency on 2m triggered from negative fronts of the input waveform, and to ensure the correlation of the operation of counters 24 and 25 Johnson, the signal at the input of the divider 23 frequency p is given with the inverted output of the divider 22. The shape of the signal at the output of the divider 23 frequency on 2m=11 shown in Fig (u23). The repetition rate of these pulses is equal to (2m/T0)/2m=1/T0.

The outputs of the counter 24 Johnson get the signals m/(2T0)with a mutual phase shift π/2 (see Fig, U24-1and u24-2), and the outputs of the counter 25 Johnson - frequency 1/4T0. The duration of the parcels on the outputs of the counter 25 Johnson is equal to 2T0.

The voltage outputs of the elements 26 and 27 “Exclusive OR” served on the shaper 32 and 33 of the sawtooth voltage. Obtained at the outputs of these shapers voltage have the form shown in the diagrams u32and u33Fig. After smoothing these stresses in the shaper 36 and 37 of the voltage sine wave voltage obtained, the shape of which is shown in the diagrams u36-1u36-2u37-1and u37-2Fig. These stresses represent a periodic sequence of segments of a sine wave with a duration 2T0hosting 2m half-periods of the oscillation frequency of mπ/T0. These oscillations have a mutual phase shift π/2.

By differentiation of the signals from the outputs of the counter 25 Johnson, and adding the received pulses in the elements 34 and 35, OR get two sequences of clock pulses (chart TI and TI, having the necessary temporary position relative to the signals at the outputs of the shapers of the voltage sine wave.

The block 21 preset, the scheme of which is shown in figure 5, together with the divider 22 frequency by two to provide synchronization of the initial actuation of the divider 23 and frequency counters 24 and 25 Johnson and necessary mutual arrangement of the output signals of the generator on the time axis in the process. It is provided as follows. At power-charging the capacitors in the base circuits of transistors (figure 5). The time constant of the charge circuit of the second capacitor is less than the first predetermined level of positive voltage at the output of the second transistor appears earlier than the first. The voltage output of the second transistor is supplied to the inputs R of the flip-flops in the divider 23 frequency and Johnson counters and sets these triggers in the same (zero) original state. After this specified level output voltage appears at the output of the first transistor, this voltage is applied to the input R of the divider 22 frequency by two and provides it a work mode (frequency division). The first positive voltage swings at the output of this divider will provide the switching of flip-flops in the divider 23 frequency and the counters 24 and 25 Johnson, which the synchronism of these in the of troist.

The unit 1 control frequency shift (figure 2), the input of which receives a modulating signal (waveform uIon Fig), generates at its output a sequence of segments of a sine wave of frequency mπ/T0where m is the desired modulation index, T0- the duration of the parcels of the modulating signal (waveform u15-16and u17-18on Fig). Consider the principle of formation of these stresses, using time charts Fig. To do this, suppose that in the first clock time begins to act first (single) sending baseband signal from the generator receives a clock pulse TI (Fig). In the moment of action of the clock pulse TI changes the state of the D-flip-flop 13. At this point in time the trigger is set in the status determined by the voltage u11the output element 11 “Exclusive OR”, and this voltage, in turn, is determined by the input signal and the voltage u14-2effective at the inverse output of the trigger 14. Assume that the voltage u14-2in the interval of the first parcel was zero (Fig). At the inputs of the element 11 has various parcels (zero and one), therefore, the output of this element is formed of a single parcel. It is a single voltage in the point of action of the first pulse TO copy the first is yhod trigger 13 and opens the key 15. Voltage S1acting on the input key will arrive at its output, i.e. to the first output control unit (waveform u15-16Fig). When the zero state of the second (inverted) output of D-flip-flop 14 of the first (direct) the output of this trigger is in a single state, i.e. u14-1=1. This voltage acts on the first input key 15. This key opens and the signal 82 from the output of the generator is fed to the input key. Thus, in the first clock interval, the first output unit 1 control frequency shift operates the signal S1and on the second output signal S2.

In the second clock time) the impulse TI. This pulse acts on D-flip-flop 14, and updates its state; the state of the D-flip-flop 13 in the second clock interval remains the same as in the first interval, i.e. one state. Thus, the inputs of the element 14 “Exclusive OR” function unit voltage on the first input - input sending, to a second input with the first output of D-flip-flop 13. Consequently, at the output of the element 12 will act zero package. In the second clock time the package will be copied to the first output of D-flip-flop 14. In this case u14-1=0, u14-2=1. Single voltage u14-2opens the key 18, through which from the generator 19 to the second output unit 1 receives a voltage S4. The first o is de block 1 will continue to operate the signal S 1.

In the beginning of the third clock pulse interval TI will change the state of the first output unit 1 control frequency shift; the state of the second output unit 1 will not change - there will continue to operate the signal S4. While in the 3rd interval on the first input element 11 operates the zero make a modulating signal, the second input - single parcel u14-2at the output of the element 11 is formed of a single voltage, 3-th clock time it will be copied to the first output of D-flip-flop 13, this voltage appears key 15, and to the first output of the unit 1 control frequency shift signal S1.

Continuing the same reasoning, we get the form of the voltages at the outputs of the functional units unit 1 corresponding to the waveform on Fig. The analysis shows that the state of the outputs of block 1 does not depend on the initial state of the D-flip-flops 13 and 14.

Sending signals from the outputs of the unit 1 control frequency shift have a duration 2T0and mutually displaced at T0just as in the MSK modulator. The phases of these sinusoids can change to π depending on the parcel (0 or 1), the current at the input of the modulator, however, the phase shift between the oscillations at any point in time is ± π/2. Given the initial phase shift between the stress rate mπ/T 0at the outputs of block 1 control frequency shift equal to π/2, the phase of the voltage at the first output of the control unit taken in the process of modulation values 0 or πand phase voltage on the second output value π/2 or 3π/2. Thus, the voltages at the outputs of the control unit of the frequency shift can be written as follows:

u1=±asin(mπt/T0), u2=±acos(mπt/T0).

Unlike MSK modulator this modulator generates parcel sinusoidal shape having not one, but 2m half-periods in the interval duration. This transformation of the rectangular input assumptions sinusoidal parcel provides the necessary (arbitrarily large), the index of modulation of the output signal of the modulator. In addition, the unit 1 control frequency shift provides a direct correspondence between the input modulating voltage of the parcel and the frequency of the output voltage of the modulator. This illustrate timing diagrams of the signals on Fig.

If the signals from the first and second outputs of the unit 1 control frequency shift apply for amplitude and phase modulators (AFM), respectively, 6 and 8 (bypassing the multiplier products 2 and 4), you will receive high-frequency signals with amplitude and phase modulation, shown in the timing charts u6and u8Fig. Send these signals mo is to imagine the following:

where ω0- frequency carrier wave coming from the generator 9.

Phase concerns parcels voltage u6takes on the values 0 or depending on the sign of the half-wave voltage at the first input of the amplitude-phase modulator 6, and the phase voltage u8accepts values π/2 or 3π/2 depending on the sign of the half-wave voltage at the first input of the amplitude-phase modulator 8. This difference of the phase voltages is determined by the phase shift on π/2 carrier wave coming from the generator 9, the phase shifter 7.

Adding the signals u6and u8in the adder 10 will receive the output voltage of the modulator:

The amplitude Uo(t) the output voltage of the modulator is constant (no AM), because

The variable component of the phase Δϕ output voltage caused by the modulation, defined:

From this equation it is seen that the interval of sending the phase of the output voltage varies linearly in time (increases or decreases). On the interval send (t=T0) change in phase will be ±mπ. The variable component of the output phase voltage of the modulator presented on Fig (time is nye chart Δ ϕ). In this timing chart, the distance between adjacent horizontal lines corresponds to the phase change Δϕ=π/2.

The variable component of the frequency Δω(t) or Δf(t) the output signal will be defined as follows:

Thus, the frequency deviation values ω0in the interval of the parcel does not depend on time. This means that the frequency deviation of the output voltage is: fd=m/2P0.

This frequency deviation is indeed corresponds to a modulation index equal to m:

The form of the variable component of the output signal of the modulator for a particular case, when not taken into account the work of the multiplier products 2 and 4, shown in Fig (timing chart fo).

With sufficiently large index modulation signal spectrum consists of two parts, symmetrically located on the axis of the frequencies relative to the carrier frequency ω0. However, the range of each part contains side lobes, the number of which increases with the modulation index. This leads to the expansion of the occupied signal bandwidth.

To reduce the bandwidth occupied by the output signal, use the multiplier products 2 and 4 (figure 1). In these multiplier products is umngeni the signals u 15-16and u17-18for smoothing a voltage generated by the generator 5 and the phase shifter 3. These stresses have the form of a periodic sequence of positive half-wave sine wave frequency π/2P0. The duration of these half-waves is equal to 2T0and the half-wave voltage received at the first inputs of the multiplier products 2 and 4, are mutually displaced at T0. The boundaries of the half-wave coincide with the boundaries of parcels received at a second input of multiplier products 2 and 4. In the result of the multiplication of the form eg parcels signals in-phase and quadrature channels corresponds to a half-wave sine wave. On Fig shows the form of the voltages at the outputs of block 1 control frequency shift (u15-16and u17-18, waveforms 1 and 2 above), the outputs of multiplier products 2 and 4 (u2and u4, waveforms 3 and 4 above) and outputs the amplitude and phase modulators 6 and 8 (u6and u8, waveforms 5 and 6 above); waveforms calculated using MathCad. In these timing charts on x-axis is the value of x=t/T0the normalized time.

Time function of the output voltage of the modulator is determined by the equation:

Included in this formula values were defined above.

Due to the action of the multiplier products 2 and 4 side lobes in the spectral characteristicallychinese signal modulator is missing, each part of the spectrum takes the form the same as the shape of the spectrum of the MSK signal. However, it should be noted that the multiplication signal and smoothing stresses in premnotes 2 and 4 and gives an undesirable effect: you receive the accompanying amplitude modulation and distortion of waveform foshown in Fig. The spectral characteristics of the output FM signal with the index of modulation m=0,5 m=5.5 and m=10,5, calculated using MathCad shown in Fig. These characteristics on the x-axis values k:

k=F·T0=F/V,

where k is the normalized frequency detuning relative to the carrier frequency;

F - absolute frequency detuning relative to the carrier frequency;

T0- the duration of sending the input modulating signal;

V - speed signal transmission.

From Fig shows that the spectrum of the signal at m=5.5 and m=10,5 divided into two equal portions, symmetrically located relative to the carrier frequency, and when m=10.5 distance between these parts of the spectrum more than when m=5,5. Thus, as the increase or decrease of the index modulation of the distance between the parts of the spectrum, respectively is increased or decreased, but the shape of these parts of the spectral characteristics of the output signal does not change. Accordingly, no change in the width of the frequency band occupied by the signal. About the aja bandwidth, occupied by the output signal of the modulator when the index of modulation m≥1,5 equal to twice the width of the signal spectrum MMS.

1. Frequency modulator split spectrum containing two multiplier, two Phaser generator sliwowska voltage, two amplitude-phase modulator, the carrier generator and the adder, and the generator output smoothing voltage is connected to the first input of the first multiplier and through the first phase shifter with the first input of the second multiplier, the output of the first multiplier is connected to the first input of the first amplitude-phase modulator, the output of the second multiplier connected to the first input of the second amplitude-phase modulator, the output of carrier generator connected to a second input of the first amplitude-phase modulator and a second phase shifter to the second input of the second amplitude-phase the modulator outputs of the first and second amplitude and phase modulators are connected respectively with the first and second inputs of the adder, the output of which is the output frequency of the modulator with the separation of the spectrum, characterized in that it includes the control unit of the frequency shift, the input of which is the input of frequency modulator with the separation of the spectrum, the first output control unit of the frequency shift is connected to the second input of the first what about the multiplier, and the second output control unit of the frequency shift is connected to the second input of the second multiplier.

2. The frequency modulator according to claim 1, characterized in that the control unit of the frequency shift contains two Exclusive OR element, two D-flip-flop, four keyand the generator, and the first inputs of XOR are interconnected and are the input of the control unit of the frequency shift, the output of the first Exclusive OR element connected to the first input of the first D-flip-flop, the output of the second Exclusive OR element connected to the first input of the second D-flip-flop, the second inputs of the first and second D-flip-flops are connected respectively with the third and fourth generator output, the first output of the first D-flip-flop is connected to the first input of the first key and the second input of the second Exclusive OR element, the second output of the first D-flip-flop is connected to the first input of the second key, the first the output of the second D-flip-flop is connected to the first input of the third key, the second output of the second D-flip-flop is connected to the first input of the fourth key and the second input of the first Exclusive OR element, the first and second outputs of the generator are connected respectively to the second input of the first key and the second input of the second key, 5-th and 6-th outputs of the generator are connected respectively to a second input of the third key and the that the fourth input key, the outputs of the first and second keys are interconnected and form a first output control unit of the frequency shift, the outputs of the third and fourth keys are interconnected and form a second output control unit of the frequency shift.

3. The frequency modulator according to claim 2, characterized in that the generator includes a master oscillator, the unit is preset, the frequency divider by two frequency divider on 2m, two of the Johnson counter, two Exclusive OR element, four differentiating circuit with a limit on the minimum, two driver sawtooth voltage, two elements OR two driver voltage sine wave and the output of the master oscillator is connected with the input of the frequency divider by two, the first output of the frequency divider by two is connected to the first input of the first Johnson counter, the second output of the frequency divider by two is connected to the first input of the frequency divider at 2m whose output is connected to the first input of the second Johnson counter, the first output unit PE is connected with the second input of the frequency divider by two, the second output unit PE is connected with the second inputs of the frequency divider on 2m and both counters Johnson, the first output of the first Johnson counter is connected to the first input of the first Exclusive OR element, the second output of the first counter Consonsilidate with the first input of the second Exclusive OR element, the first output of the second Johnson counter is connected with the second input of the first Exclusive OR element and to the input of the first differential circuit with a limit on the minimum, the second output of the second Johnson counter is connected with the input of the second differentiating circuit, the third output of the second Johnson counter is connected with the second input of the second Exclusive OR element and to the input of the third differential circuit with a limit on the minimum, the fourth output of the second Johnson counter is connected with the input of the fourth differential circuit with a limit on the minimum, the output of the first Exclusive OR element is connected with the input of the first driver of the sawtooth voltage, the output of the second Exclusive OR element is connected with the input of the second driver the sawtooth voltage, the output of the first driver of the sawtooth voltage is connected with the input of the first driver voltage sine wave output, two outputs which are the first and second outputs of the generator, the output of the second shaper of the sawtooth voltage is connected with the input of the second driver voltage sine wave output, two outputs which are the fifth and sixth outputs of the generator, the output of the first and second differentiating circuit with a limit on the minimum connected with the inputs of the first element of the and, OR, the output of which is the third generator output, the output of the third and fourth differentiating circuit with a limit on the minimum connected with the inputs of the second element OR the output of which is the fourth generator output.



 

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