CN104580046A - V-F conversion-based 2FSK modulation circuit - Google Patents

Abstract

The invention discloses a V-F conversion-based 2FSK modulation circuit. The V-F conversion-based 2FSK modulation circuit at least comprises an integrating circuit, a hysteresis comparator, a discharge switch circuit and a sine wave shaping circuit, wherein the integrating circuit is used for generating a triangular wave output which is in proportion to a first input control voltage; the hysteresis comparator is used for converting the triangular wave output by the integrating circuit into a square wave to control the discharge switch circuit; the discharge switch circuit is used for discharging to an integrating capacitor of the integrating circuit regularly under the control of the hysteresis comparator; the sine wave shaping circuit is used for converting the triangular wave into a continuous-phase sine wave. According to the V-F conversion-based 2FSK modulation circuit, continuous-phase 2FSK is realized without an additional frequency source by utilizing the characteristic that the oscillation frequency of an output rectangular wave is in direct proportion to the control voltage by V-F conversion, improving the circuit, adding series of waveform conversion circuits, and then outputting the sine wave which changes between two different frequencies according to the change of two levels of the control voltage.

Description

A kind of 2FSK modulation circuit based on V-F conversion

Technical field

The present invention relates to a kind of 2FSK modulation circuit, particularly relate to a kind of 2FSK modulation circuit based on V-F conversion.

Background technology

Along with popularizing of electronic computer, digital communication technology obtains and develops rapidly, digital frequency modulation is a kind of modulation system common in digital communication, frequency shift keying (FSK) method is simple, be easy to realize, and demodulation does not need to recover local carrier, can asynchronous transmission, antinoise and anti fading performance stronger, apply very extensive in middle slow data transmission.

FSK utilizes the change of carrier frequency to carry out transmitting digital information.2FSK refers to that baseband signal " 1 " is corresponding to carrier frequency f1, the modulated waveform of corresponding another carrier frequency f0 of baseband signal " 0 ", and the change between f1 and f0 completes instantaneously.Expression formula as shown in Equation 1.

2FSK modulator approach mainly contains two kinds.One is frequency modulation method, carries out frequency modulation by a square pulse to a carrier wave, produces the digital frequency-modulation signal of Phase Continuation; Another kind is shoulder rotation, utilizes the switching circuit that square pulse controls, and carries out gating to two different independent frequency sources, because the phase place between frequency source is uncorrelated mutually, easily produces the digital frequency-modulation signal of phase dispersion.

In sum, the 2FSK modulator approach of prior art exists needs impressed frequency source, and due to the phase place between frequency source uncorrelated mutually, the problem of the digital frequency-modulation signal of easy generation phase dispersion, therefore, be necessary to propose a kind of technological means, to solve the problem in fact.

Summary of the invention

For overcoming the deficiency that above-mentioned prior art exists, the object of the present invention is to provide a kind of 2FSK modulation circuit based on V-F conversion, it utilizes V-F to change the characteristic that the frequency of oscillation of output square wave is directly proportional to control voltage, and circuit is improved, increase serial waveform transformation circuit, according to two kinds of level changes of control voltage, export the sine wave changed between two kinds of different frequencies thereupon, thus when without impressed frequency source, realize the 2FSK modulation of Phase Continuation.

For reaching above-mentioned and other object, the present invention proposes a kind of 2FSK modulation circuit based on V-F conversion, at least comprises:

Integrating circuit, exports for generation of one and the proportional triangular wave of the first input control voltage;

Hysteresis comparator, the triangular wave for being exported by this integrating circuit is converted to square wave and exports with controlled discharge switching circuit;

Discharge switching circuit, discharges to the integrating capacitor of this integrating circuit for timing under the control of this hysteresis comparator;

Sine wave shaped circuit, for being converted to the sine wave of Phase Continuation by this triangular wave.

Further, this integrating circuit comprises the first resistance, 3rd resistance, 4th resistance, first electric capacity and the first comparator, 3rd resistance one end connects the first input control voltage, the inverting input of this first electric capacity of another termination and the first comparator, the output of this this first comparator of another termination of the first electric capacity, this first input control voltage is through the 4th resistance, a voltage is obtained after first electric resistance partial pressure, this voltage accesses the in-phase input end of this first comparator to control the time of integration of this integrating circuit, the output of this first comparator is the charging/discharging voltage of approximate triangular wave.

Further, output one tunnel of this first comparator is connected to this hysteresis comparator, and another road is connected to this sine wave shaped circuit.

Further, this discharge switching circuit comprises the second resistance, the 5th resistance and the first triode, this the first transistor emitter ground connection, its collector electrode is connected to the inverting input of this first comparator through this second resistance, and its base stage is connected to the output of this hysteresis comparator through the 5th resistance.

Further, this hysteresis comparator comprises the 6th resistance, the 7th resistance and the second comparator, 6th resistance one termination second control voltage, the in-phase input end of another termination the 7th resistance and this second comparator, the output of the 7th this second comparator of another termination of resistance, the output of this second comparator is connected to the base stage of this first triode through the 5th resistance.

Further, this sine wave shaped circuit comprises the 8th to the 15 resistance, 18 resistance, first variable resistor, the second adjustable resistance, 2nd NPN triode, 3rd NPN triode, 4th PNP triode, 5th PNP triode, one end of 15 resistance connects the output of this first comparator, the variable resistor end of this second adjustable resistance of another termination, the variable resistor end of this second adjustable resistance and shorted on one end and one end of another termination the 2nd NPN transistor base and the 13 resistance, this first variable resistor is connected between positive supply and ground, a bias voltage is exported at its variable resistor end, the base stage that this bias voltage is connected to the 2nd NPN triode through the 14 resistance makes the 2nd NPN triode operation in the center of sigmoid curve, 2nd NPN triode and the 3rd NPN transistor emitter are by the tenth resistance, 11 resistance is connected to one end of the 12 resistance, another termination negative supply of 12 resistance, the collector electrode of the 2nd NPN triode connects base stage and the collector electrode of the 4th PNP triode, the collector electrode of the 3rd NPN triode connects the collector electrode of the 5th PNP triode and one end of the 18 resistance, the other end of the 18 resistance and the base earth of the 3rd NPN triode, 4th PNP triode is connected back-to-back with the base stage of the 5th PNP triode, the emitter of the 4th PNP triode and the 5th PNP triode is respectively by the 8th resistance, 9th resistance is connected to positive supply.

Further, the output of this first comparator is connected to one end of the 15 resistance through capacitance.

Further, the tenth resistance and the 11 resistance are substitutional resistance, and the 8th resistance and the 9th resistance are substitutional resistance.

Compared with prior art, a kind of 2FSK modulation circuit based on V-F conversion of the present invention is by arranging the level change of control voltage, V-F change-over circuit is made to export the square wave changed between two kinds of different frequencies, and V-F change-over circuit is improved, according to two kinds of level changes of control voltage, export the sine wave changed between two kinds of different frequencies thereupon, the complexity of circuit can be reduced on the one hand, make circuit structure succinct, the error in waveform transformation process can be reduced on the other hand, improve the accuracy of circuit.

Accompanying drawing explanation

Fig. 1 is typical V-F change-over circuit figure;

Fig. 2 is the transmission characteristic schematic diagram of difference pipe;

Fig. 3 is the circuit structure diagram of a kind of 2FSK modulation circuit based on V-F conversion of the present invention;

The 2FSK signal that Fig. 4, Fig. 5, Fig. 6 are respectively the V-F transformation result of simulation result of the present invention, triangular wave exports and exports.

Embodiment

Below by way of specific instantiation and accompanying drawings embodiments of the present invention, those skilled in the art can understand other advantage of the present invention and effect easily by content disclosed in the present specification.The present invention is also implemented by other different instantiation or is applied, and the every details in this specification also can based on different viewpoints and application, carries out various modification and change not deviating under spirit of the present invention.

Before introducing the present invention, V-F transfer principle once is first described:

Fig. 1 is typical V-F change-over circuit figure.As shown in Figure 1, A1, C1, R1 etc. form integrating circuit.A2, R5, R7 etc. form hysteresis loop comparator, and its reference voltage is E2, and its output packet is containing exporting upper limit VOM and bottoming-VOM two states.Circuit exports vO controls triode T1 conducting and cut-off through feedback branch, and then the discharge and recharge time of control capacitance C1.The numerical value change of input voltage E1 determines A1 in-phase input end current potential VP1, thus controls the time of integration of integrating circuit, and the frequency of output signal is changed thereupon.

Can obtain the hysteresis loop comparator circuit analysis that A2, R5, R7 etc. are formed, A2 homophase input voltage is such as formula shown in (2)

$v_{P2}=\frac{R_7}{R_5+R_7}{E}_2+\frac{R_5}{R_5+R_7}{v}_O---\left(2\right)$

Comparator turn threshold is corresponding as follows:

V _o=+V _oMtime,

$V_{\mathrm{AH}}=\frac{R_7}{R_5+R_7}{E}_2+\frac{R_5}{R_5+R_7}{V}_{\mathrm{OM}}---\left(3\right)$

V _o=-V _oMtime,

$V_{\mathrm{AL}}=\frac{R_7}{R_5+R_7}{E}_2-\frac{R_5}{R_5+R_7}{V}_{\mathrm{OM}}---\left(4\right)$

Suppose R ₅=100K Ω, R ₇=200K Ω, is obtained by formula (3), formula (4)

$V_{\mathrm{AH}}=\frac{2}{3}{E}_2+\frac{1}{3}{V}_{\mathrm{OM}}---\left(5\right)$

$V_{\mathrm{AL}}=\frac{2}{3}{E}_2-\frac{1}{3}{V}_{\mathrm{OM}}---\left(6\right)$

Work as v _o=+V _oMtime, triode T1 is saturated, ignores saturation voltage drop,

$\frac{E_1-V_{P1}}{R_1}+C_1\frac{d(v_C-V_{P1})}{\mathrm{dt}}=\frac{V_{P1}}{R_3}---\left(7\right)$

Wherein formula (7) abbreviation obtains

$C_1\frac{{\mathrm{dv}}_C}{\mathrm{dt}}=(\frac{1}{R_3}+\frac{1}{R_1})V_{P1}-\frac{E_1}{R_1}---\left(8\right)$

If R ₁=100K Ω, R ₂=R ₃=R ₄=50K Ω,

$v_C=\frac{1}{2\×{10}^5}\frac{E_1}{C_1}\∫\mathrm{dt}+V_{\mathrm{AL}}---\left(9\right)$

Work as v _o=-V _oMtime, triode T1 ends,

$\frac{E_1-V_{P1}}{R_1}=-C_1\frac{d(v_C-V_{P1})}{\mathrm{dt}}=-C_1\frac{{\mathrm{dv}}_C}{\mathrm{dt}}---\left(10\right)$

$v_C=-\frac{1}{2\×{10}^5}\frac{E_1}{C_1}\∫\mathrm{dt}+V_{\mathrm{AH}}---\left(11\right)$

Convolution (5) and formula (9) are analyzed

$\frac{2}{3}{E}_2+\frac{1}{3}{V}_{\mathrm{OM}}=\frac{1}{2\×{10}^5}\frac{E_1}{C_1}\∫\mathrm{dt}+\frac{2}{3}{E}_2-\frac{1}{3}{V}_{\mathrm{OM}}---\left(12\right)$

VO low level time is

$T_L=\frac{4\×{10}^5}{3}\frac{V_{\mathrm{OM}}\·C_1}{E_1}---\left(13\right)$

Convolution (6) and formula (11) are analyzed

$\frac{2}{3}{E}_2-\frac{1}{3}{V}_{\mathrm{OM}}=-\frac{1}{2\×{10}^5}\frac{E_1}{C_1}\∫\mathrm{dt}+\frac{2}{3}{E}_2+\frac{1}{3}{V}_{\mathrm{OM}}---\left(14\right)$

VO high level time is

$T_H=\frac{4\×{10}^5}{3}\frac{V_{\mathrm{OM}}\·C_1}{E_1}---\left(15\right)$

So frequency of oscillation is

$f=\frac{1}{T_H+T_L}=\frac{{3E}_1}{8\×{10}^5{V}_{\mathrm{OM}}\·C_1}---\left(16\right)$

To sum up, oscillation output signal is square wave, and frequency is with input voltage E1 linear change.

Visible, V-F change-over circuit can make the frequency of oscillation of output square wave be directly proportional to control voltage, and for realizing 2FSK modulation, the present invention makes further improvements on V-F change-over circuit basis, realize according to two kinds of different incoming levels, the corresponding sine wave exporting two kinds of different frequencies.Usually, be first triangular wave through Integral Transformation by square wave, and then be converted to sine wave through waveform transformation.Obtain through circuit analysis, integrating circuit in V-F change-over circuit itself can produce the triangular wave identical with the square wave frequency by producing after hysteresis loop comparator, therefore, the present invention is using directly the input signal of this triangular wave as translation circuit, after chain of circuits conversion, produce corresponding sine wave, the complexity of circuit can be reduced on the one hand, make circuit structure succinct, the error in waveform transformation process can be reduced on the other hand, improve the accuracy of circuit.

In the present invention, the nonlinear transmission characteristic of differential amplifier circuit is utilized to realize the conversion of triangular wave-sine wave.According to the differential mode transmission characteristic of typical differential amplifier circuit, the relation between its output current (voltage) and differential-mode input voltage meets the Changing Pattern of hyperbolic tangent function.When triangular wave inputs the saturation region close to difference pipe, output waveform is scabbled by sigmoid curve as shown in Figure 2, when namely inputting suitable voltage, output can be made to be in close proximity to sine wave.In order to make output waveform closer to sine wave, the transmission characteristic of differential amplifier circuit should be symmetrical as far as possible, and linear zone is more narrow better.

Fig. 3 is the circuit structure diagram of a kind of 2FSK modulation circuit based on V-F conversion of the present invention.As shown in Figure 3, the 2FSK modulation circuit of a kind of V-F conversion of the present invention, comprise integrating circuit 10, hysteresis comparator 20, discharge switching circuit 30, sine wave shaped circuit 40, integrating circuit 10 is by resistance R1, R3-4, electric capacity C1 and comparator U1 forms, export for generation of one and the proportional triangular wave of the first input control voltage, hysteresis comparator 20 is by resistance R6, R7 and comparator U2 forms, triangular wave for being exported by integrating circuit 10 is converted to square wave and exports with controlled discharge switching circuit 30, discharge switching circuit 30 is by resistance R5, R2 and triode Q1 forms, for timing under the control of hysteresis comparator 20, the integrating capacitor C1 of integrating circuit 10 is discharged, sine wave shaped circuit 40 is by resistance R8-15, R18, variable resistor R16-17 (being respectively the first variable resistor and the second adjustable resistance), NPN forms pipe Q4-5 pipe Q2-3 and PNP, wherein PNP forms mirror-image constant flow source (proportion current source) to pipe Q4-5 and resistance R8-9, NPN forms differential amplifier to pipe Q2-3 and resistance R10-11, for triangular wave being converted to the sine wave of Phase Continuation, C2 is capacitance.First input control voltage V4 is changed into digital " 0 ", " 1 " series, then can export the sinusoidal wave 2FSK voltage of modulated continuous phase at the collector electrode of NPN triode Q3.

Resistance R3, electric capacity C1 and comparator U1 forms the integrating circuit of integrator, R3 one end connects the first input control voltage V4, the inverting input of another termination capacitor C1 and comparator U1, the output of another termination comparator of C1 U1, V4 is the first input control voltage, it is through resistance R4, voltage Vp1 is obtained after R1 dividing potential drop, this voltage Vp1 accesses the in-phase input end of comparator U1 to control the time of integration of integrator, resistance R2 and triode Q1 forms the discharge channel of integrating circuit, comparator U1 exports as charging/discharging voltage, this voltage is approximately a triangular wave (when time constant R3 × C1 is larger), this triangular wave one tunnel is connected to resistance R6, the inverting input of the hysteresis comparator that R7 and comparator U2 forms, resistance R6 mono-termination second control voltage V2, the in-phase input end of other end connecting resistance R7 and comparator U2, the output of another termination comparator of resistance R7 U2, the output of comparator U2 is connected to the base stage of triode Q1 through resistance R5, triode Q1 grounded emitter, its collector electrode is connected to the inverting input of comparator U1 through resistance R2, another road of triangular wave of comparator U1 output is connected to the input of sine wave shaped circuit and one end of resistance R15 after capacitance C2, the variable resistor end of another termination variable resistor of resistance R15 R17, the variable resistor end of variable resistor R17 and shorted on one end and one end of another termination NPN triode Q2 base stage and resistance R13, variable resistor R16 is connected between VCC and ground, a bias voltage is exported at its variable resistor end, the base stage that this bias voltage is connected to NPN triode Q2 through resistance R14 makes Q2 work in the center of sigmoid curve, NPN triode Q2 and Q3 emitter are by substitutional resistance R10, R11 is connected to one end of resistance R12, another termination negative supply VEE of resistance R12, the collector electrode of NPN triode Q2 connects base stage and the collector electrode of PNP triode Q4, the collector electrode of NPN triode Q3 connects the collector electrode of PNP triode Q5 and one end of resistance R18, the base earth of the resistance R18 other end and NPN triode Q3, PNP triode Q4 is connected back-to-back with the base stage of Q5, the emitter of PNP triode Q4 and Q5 is respectively by substitutional resistance R8, R9 is connected to positive supply VCC.

The 2FSK signal that Fig. 4, Fig. 5, Fig. 6 are respectively the V-F transformation result of simulation result of the present invention, triangular wave exports and exports.The ERC of circuit check errorless after, at the input of 2FSK modulation circuit, add binary sequence " 0101 ", after setting suitable bias voltage, as shown in Figure 4, code element " 1 " and " 0 " correspondence export the square wave of 2.5KHz and 833Hz, substantially meet principle analysis result.The triangular wave that integrating circuit exports is as shown in Figure 5, consistent with square wave frequency.After triangular wave-sine wave conversion, as shown in Figure 6, corresponding code element " 1 " and " 0 " export the sine wave of 2.5KHz and 833Hz to the 2FSK signal of output respectively, Phase Continuation, and waveform transition is comparatively steady, and amplitude is consistent.

Pass through analysis of simulation result, the 2FSK modulation circuit of the present invention is when without impressed frequency source, corresponding baseband signal " 1 " and baseband signal " 0 " output the sine wave of two kinds of frequencies respectively, and Phase Continuation, waveform transition is more level and smooth, conform to Analysis of Electric Circuit Theory, reach needs of expected design.

In sum, a kind of 2FSK modulation circuit based on V-F conversion of the present invention is by arranging the level change of control voltage, V-F change-over circuit is made to export the square wave changed between two kinds of different frequencies, and V-F change-over circuit is improved, according to two kinds of level changes of control voltage, export the sine wave changed between two kinds of different frequencies thereupon, the complexity of circuit can be reduced on the one hand, make circuit structure succinct, the error in waveform transformation process can be reduced on the other hand, improve the accuracy of circuit.

Above-described embodiment is illustrative principle of the present invention and effect thereof only, but not for limiting the present invention.Any those skilled in the art all without prejudice under spirit of the present invention and category, can carry out modifying to above-described embodiment and change.Therefore, the scope of the present invention, should listed by claims.

Claims (8)

1., based on a 2FSK modulation circuit for V-F conversion, at least comprise:

Integrating circuit, exports for generation of one and the proportional triangular wave of the first input control voltage;

Hysteresis comparator, the triangular wave for being exported by this integrating circuit is converted to square wave and exports with controlled discharge switching circuit;

Discharge switching circuit, discharges to the integrating capacitor of this integrating circuit for timing under the control of this hysteresis comparator;

Sine wave shaped circuit, for being converted to the sine wave of Phase Continuation by this triangular wave.

2. as claimed in claim 1 a kind of based on V-F conversion 2FSK modulation circuit, it is characterized in that: this integrating circuit comprises the first resistance, 3rd resistance, 4th resistance, first electric capacity and the first comparator, 3rd resistance one end connects the first input control voltage, the inverting input of this first electric capacity of another termination and the first comparator, the output of this this first comparator of another termination of the first electric capacity, this first input control voltage is through the 4th resistance, a voltage is obtained after first electric resistance partial pressure, this voltage accesses the in-phase input end of this first comparator to control the time of integration of this integrating circuit, the output of this first comparator is the charging/discharging voltage of approximate triangular wave.

3. as claimed in claim 2 a kind of based on V-F conversion 2FSK modulation circuit, it is characterized in that: output one tunnel of this first comparator is connected to this hysteresis comparator, and another road is connected to this sine wave shaped circuit.

4. as claimed in claim 3 a kind of based on V-F conversion 2FSK modulation circuit, it is characterized in that: this discharge switching circuit comprises the second resistance, the 5th resistance and the first triode, this the first transistor emitter ground connection, its collector electrode is connected to the inverting input of this first comparator through this second resistance, and its base stage is connected to the output of this hysteresis comparator through the 5th resistance.

5. as claimed in claim 4 a kind of based on V-F conversion 2FSK modulation circuit, it is characterized in that: this hysteresis comparator comprises the 6th resistance, the 7th resistance and the second comparator, 6th resistance one termination second control voltage, the in-phase input end of another termination the 7th resistance and this second comparator, the output of the 7th this second comparator of another termination of resistance, the output of this second comparator is connected to the base stage of this first triode through the 5th resistance.

6. as claimed in claim 5 a kind of based on V-F conversion 2FSK modulation circuit, it is characterized in that: this sine wave shaped circuit comprises the 8th to the 15 resistance, 18 resistance, first variable resistor, the second adjustable resistance, 2nd NPN triode, 3rd NPN triode, 4th PNP triode, 5th PNP triode, one end of 15 resistance connects the output of this first comparator, the variable resistor end of this second adjustable resistance of another termination, the variable resistor end of this second adjustable resistance and shorted on one end and one end of another termination the 2nd NPN transistor base and the 13 resistance, this first variable resistor is connected between positive supply and ground, a bias voltage is exported at its variable resistor end, the base stage that this bias voltage is connected to the 2nd NPN triode through the 14 resistance makes the 2nd NPN triode operation in the center of sigmoid curve, 2nd NPN triode and the 3rd NPN transistor emitter are by the tenth resistance, 11 resistance is connected to one end of the 12 resistance, another termination negative supply of 12 resistance, the collector electrode of the 2nd NPN triode connects base stage and the collector electrode of the 4th PNP triode, the collector electrode of the 3rd NPN triode connects the collector electrode of the 5th PNP triode and one end of the 18 resistance, the other end of the 18 resistance and the base earth of the 3rd NPN triode, 4th PNP triode is connected back-to-back with the base stage of the 5th PNP triode, the emitter of the 4th PNP triode and the 5th PNP triode is respectively by the 8th resistance, 9th resistance is connected to positive supply.

7. as claimed in claim 6 a kind of based on V-F conversion 2FSK modulation circuit, it is characterized in that: the output of this first comparator is connected to one end of the 15 resistance through capacitance.

8. as claimed in claim 6 a kind of based on V-F conversion 2FSK modulation circuit, it is characterized in that: the tenth resistance and the 11 resistance are substitutional resistance, the 8th resistance and the 9th resistance are substitutional resistance.