CN207304507U - Small-signal input square-wave generator based on Schmitt trigger - Google Patents
Small-signal input square-wave generator based on Schmitt trigger Download PDFInfo
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- CN207304507U CN207304507U CN201721228367.4U CN201721228367U CN207304507U CN 207304507 U CN207304507 U CN 207304507U CN 201721228367 U CN201721228367 U CN 201721228367U CN 207304507 U CN207304507 U CN 207304507U
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Abstract
The utility model discloses a kind of generator by small-signal input Schmitt trigger generation rectangular wave, it includes small-signal termination power, feedback circuit, DC bias circuit, carrier circuit.The small-signal termination power, passes through coupled capacitor C by the small-signal of prime1It is fed to Schmidt trigger input terminal.The feedback circuit, trigger output terminal signal level by R2/C2It is average, and feed back to Schmitt trigger input terminal.The DC bias circuit, 15V direct current supplys voltage pass through potentiometer P1And capacitor C2Apply a DC offset voltage U to trigger input terminalZ.The carrier circuit, Dc bias UZPass through resistance R1It is " trimmed（Superposition）To passing through capacitance C1In the amplitude of the AC signal of input, the level of the mixed signal after superposition, exactly improves Dc bias amplitude on the basis of original small-signal, and the so-called carrier signal of the communications field is exactly to realize around this principle in fact.
Description
Technical field
A kind of technology by small-signal generation rectangular wave is the utility model is related to, it is especially a kind of to export general sensor
The equipment that small-signal generates rectangular wave by Schmidt trigger.
Background technology
A certain signal is transformed to rectangular wave using Schmidt trigger, it is widely used.Schmidt trigger is a kind of
Special gate circuit, different from common gate circuit, Schmidt trigger has two threshold voltages, is referred to as positive threshold electricity
Press U+With negative sense threshold voltage U--.Circuit state is set to change during input signal rises to high level from low level
Input voltage be known as forward threshold voltage, input signal from high level drop to it is low level during send out circuit state
The input voltage for changing is known as negative sense threshold voltage.Forward threshold voltage and the difference of negative sense threshold voltage are known as hysteresis voltage.
This voltage-transfer characteristic curve is known as " hysteresis curve " of Schmidt trigger, sees attached drawing 1.
Certainly, the duty cycle of Schmidt trigger output end signal and frequency each depend on the waveform of input signal.It is but real
On border, the waveform of input signal is unimportant, and the basic demand of Schmidt trigger normal work to be made is that input signal is necessary
Exceed or at least up to threshold value of Schmidt trigger（Or threshold value）, i.e., the input voltage in uphill process have to be larger than U+
Input voltage during voltage, decline have to be larger than U-- voltages, and Schmidt trigger output voltage can just invert.
Based on principles above, if wishing tiny signal generating rectangular wave, the side generally used by Schmitt trigger
Method is nothing more than two kinds, one is by the way of step-up transformer AC coupled, the second is the side using preamplifier circuit
Formula, the thinking of two ways is close, is all to be amplified to small-signal to meet Schmitt trigger required standard signal first,
The output voltage of Schmidt trigger can invert, but be also fatal the shortcomings that two methods, can be discussed in detail below.
Design it is a kind of on Schmidt trigger how by small-signal generation rectangular wave controller, using this control
The Schmidt trigger of device, limits, the ideal input signal of the trigger for so-called threshold value of the input signal without more than
Exactly common Schmidt trigger can not produce the small-signal of output waveform.This circuit can keep identical to various input signals
Sensitivity, it is and unrelated with waveform input signal and amplitude.
The content of the invention
Technical problem to be solved in the utility model be to provide it is a kind of it is simple in structure, using it is reliable, former electricity will not be changed
Road input, output characteristics, can easily realize that the small-signal for exporting general sensor is given birth to by Schmidt trigger
The equipment of rectangular ripple, this circuit can keep various input signals identical sensitivity, and with waveform input signal and amplitude
It is unrelated.
To achieve the above object, the utility model provides a kind of small-signal input rectangular wave hair based on Schmitt trigger
Raw device, it includes small-signal termination power, Schmitt flip-flop circuit, feedback circuit, DC bias circuit, carrier circuit group
Into；The small-signal of prime sensor output enters Schmitt flip-flop circuit, trigger electricity by small-signal termination power
The output signal on road feeds back to Schmitt trigger input terminal after feedback circuit is handled, and DC bias circuit is to trigger
Input terminal applies a DC offset voltage UZ, Dc bias UZPass through resistance R1" trimmed arrive passes through capacitance C1What is inputted is micro-
In the amplitude of weak AC signal, input signal improves Dc bias amplitude, i.e. carrier wave principle on the basis of original small-signal.
The small-signal termination power, the small-signal that prime sensor exports is fed by coupled capacitor C1
To Schmidt trigger input terminal.
The feedback circuit, is averaged in the signal level of trigger output terminal by R2/C2, and feeds back to Schmitt triggering
Device input terminal.
The DC bias circuit, by 15V direct current supplys voltage by potentiometer P1 and capacitor C2 to trigger
Input terminal applies a DC offset voltage UZ.
The carrier circuit, it is " trimmed by resistance R1 by Dc bias UZ（Superposition）To what is inputted by capacitance C1
In the amplitude of faint AC signal, the level of the mixed signal after superposition, exactly improves straight on the basis of original small-signal
Bias amplitude is flowed, the so-called carrier signal of the communications field is exactly to realize around this principle in fact.
Brief description of the drawings
Attached drawing 1, attached drawing 2, attached drawing 3, attached drawing 4, attached drawing 5, attached drawing 6 are used to provide a further understanding of the present invention,
The part of the application is formed, attached drawing 1 is Schmidt trigger " hysteresis curve " curve map, and attached drawing 2 is Schmidt trigger
Filtering schematic diagram to small-signal, attached drawing 3 is that step-up transformer AC coupled realizes that WeChat ID generates rectangular wave schematic diagram, attached
Fig. 4 is common emitter amplifier circuit diagram, and attached drawing 5 is that WeChat ID is generated rectangular wave electrical schematic diagram, attached drawing 6 using carrier wave principle
It is that tiny signal is generated into rectangular wave schematic diagram using carrier wave principle.
Embodiment
Attached drawing 5 is the electric of the input square-wave generator of the small-signal based on Schmitt trigger of the utility model design
Schematic diagram, including small-signal termination power, Schmitt flip-flop circuit, feedback circuit, DC bias circuit, carrier circuit,
The present invention is described in detail below.
Known Schmidt trigger requires that input signal must be over or at least up to so-called threshold value just can be with above
Output signal is overturn, some small-signals can not possibly invert output signal, the signal conduct as shown in the A in attached drawing 2
Input can produce output rectangular wave in trigger, and B signal exports if trigger is added to without waveform.
In order to handle the less faint input signal of amplitude, rectangle can be generated by Schmitt trigger
Ripple, may be referred to following several schemes.
By the way of step-up transformer AC coupled：For the less faint input signal of amplitude, boosting can be used
The mode of transformer alternating coupling amplifies small-signal, so that input signal exceedes required threshold value, such as attached drawing 3
It is shown.
In attached drawing 3, capacitance C1 is small-signal input coupling capacitance, and for transformer primary and secondary, capacitance, IC1 are capacitance C2 altogether
Schmitt trigger, the AC signal of 0.5V, can about be boosted to a 5V left sides by transformer T primary and secondary turn ratios N2/N1=12
The right side, so that useful signal amplitude exceedes the required threshold value of Schmidt trigger, Schmidt trigger can be defeated in theory
Go out a rectangular wave, but transformer primary and secondary D.C. resistance is all minimum, and this will certainly influence the univers parameter of circuit, such as circuit
Input resistance, output resistance etc..
By the way of preamplifier circuit：It is of course also possible to use the mode of preamplifier circuit, equally will be micro-
Small signals amplification reaches threshold value needed for Schmitt trigger, can be given birth to so as to fulfill faint small-signal by Schmitt trigger
Rectangular ripple, such as attached drawing 4.
Amplifying circuit shown in attached drawing 4 is most basic common emitter amplifying circuit, its quiescent point voltage request is base stage
Positively biased, collector is reverse-biased, and Ui is faint small-signal to be treated, and Vcc is direct-current working volts.Final result is to work as triode
During the B poles input small-signal of Q, C pole tensions will surround quiescent voltage Vcc and fluctuate, and Uo signal amplitudes at this moment already exceed Shi Mi
The special required threshold value of trigger, is the standard signal for meeting Schmitt trigger input requirements, by Uo signals as Fig. 3
Access Schmitt trigger IC1：The input terminal of CD40106, IC1 can be with the square-wave signals of outputting standard.
Above two method can be no doubt realized the imagination of small-signal output rectangular wave, but increases the design of circuit
Difficulty, it is more serious the shortcomings that be the input resistance that drastically reduced operation amplifier circuit, the defeated of amplifier is put in present computing
It is all very high to enter impedance, so amplifier input end signal lever selection leeway is bigger, but electricity is coupled according to step-up transformer
The input resistance of interlock circuit can be but reduced to tens of Ohms by the mode on road, this can seriously affect front stage circuits output resistance ginseng
Several choices, it is total to know from experience the serious sensitivity for reducing system.
Common emitter amplifier can obtain higher voltage amplification factor, but its input resistance is smaller, and output resistance is larger, such as
It is the same with the mode that step-up transformer termination power is used above, more than the selection that can equally influence front stage circuits output resistance parameter
Ground, reduces the sensitivity of whole system.
Emitter-follower（Common-collector amplifier）It is a kind of reason with higher input resistance and less output resistance
The output-stage circuit and input stage circuit thought, but its voltage amplification factor is about 1, does not meet the most basic requirement of the design.
WeChat ID is generated into rectangular wave using carrier wave principle：According to the design circuit of attached drawing 5, former computing will not be changed and put
The input of big device, output characteristics, can but solve set forth above to export rectangular wave by Schmidt trigger on small-signal
The problem of, this circuit can keep identical sensitivity to any input signal, and unrelated with waveform input signal, amplitude.
Trigger N1 models CD40106, CD40106 are made of six Schmitt flip-flop circuits used in the circuit.Often
A circuit is the phase inverter for having Schmitt trigger function in two input terminals.Trigger input signal rising edge and under
Edge, corresponding two different threshold point output " 0 " logics or " 1 " logic drop.The difference of raised voltage V+ and drop-out voltage V- are determined
Justice is lagging voltage.
Circuit design is very simple, it is well understood that including small-signal termination power, feedback circuit, DC bias circuit, load
Wave circuit forms.The small-signal of prime sensor output is fed to Schmidt trigger input terminal by coupled capacitor C1,
In trigger output terminal, signal level is averaged by R2/C2, and feeds back to input terminal.15V direct current supplys voltage passes through potentiometer P1
And capacitor C2 applies a DC offset voltage U to trigger input terminalZ, the Dc bias is " trimmed by resistance R1
（Superposition）Onto the amplitude of the AC signal inputted by capacitance C1, the level of mixed signal after superposition, i.e., in original faint letter
Dc bias amplitude is improved on the basis of number, the so-called carrier signal of the communications field is exactly to realize around this principle in fact.
The input impedance of operational amplifier is all very high, the trigger typical input bias current only 2pA, such input terminal
The resistance value of outer connecting resistance can be very big, such as the disturbance voltage of 1 μ V corresponds to：
R==500k
It is 1M Ω that the design, which chooses the outer connecting resistance R1 resistance values of input terminal,.
Final result is exactly that any amplitude is more than Schmidt trigger threshold value（Magnetic hysteresis value）The difference of signal will be
Its output terminal produces a rectangular wave, as shown in Figure 6, U in figureZAs DC offset voltage, is exactly this bias voltage, makes defeated
The voltage magnitude for entering small-signal exceedes the threshold voltage of trigger.
Can so it understand, can be with by giving Schmidt trigger input terminal to apply a suitable bias voltage in circuit
Adjust input signal and two threshold value U+And U--Relation, the size of bias voltage is adjusted by potentiometer P1, therefore Schmidt
The sensitivity that trigger can export rectangular wave is adjusted by potentiometer P1.
The deficiency for being designed WeChat ID generation sawtooth waveforms using carrier wave principle：The design circuit also has unsatisfactoryly
Side, when input terminal does not have signal, circuit just works as a self-excited oscillator.When there is signal, this is produced in order to prevent
The frequency of oscillation of kind phenomenon, R2 and C2 must be at least below 10 times of this circuit institute frequency of use（This channel frequency is
100Hz）.So the circuit can be used as the preferable automatic trigger of oscillograph.
Design another disadvantage is that, it is not suitable for the extremely narrow input signal of duty cycle, due to this kind of signal by a narrow margin
Degree is poor, can be broken output pulse train.
Small-signal input square-wave generator circuit structure based on Schmitt trigger is simple, thinking is ingenious, the design
Not by the way of step-up transformer AC coupled and preamplifier circuit mode, and use faint AC signal is carried
For the method for a direct current biasing by a relatively large margin, perfection, which realizes small-signal, to form rectangular wave by Schmidt trigger
Contemplate, and completely no any input for changing former operational amplifier, output characteristics, although there are many shortcomings, but pass through modification
Circuit parameter can avoid these shortcomings as possible.
Claims (4)
1. the small-signal input square-wave generator based on Schmitt trigger, it is characterised in that：It includes small-signal coupling
Circuit, Schmitt flip-flop circuit, feedback circuit, DC bias circuit, carrier circuit composition；Prime sensor exports faint
Signal enters Schmitt flip-flop circuit by small-signal termination power, and the output signal of flip-flop circuit passes through feedback circuit
Schmitt trigger input terminal is fed back to after processing, DC bias circuit applies a direct current biasing electricity to trigger input terminal
Press UZ, Dc bias UZPass through resistance R1It is finished to by capacitance C1In the amplitude of the faint AC signal of input, input signal
Dc bias amplitude, i.e. carrier wave principle are improved on the basis of original small-signal.
2. the small-signal input square-wave generator according to claim 1 based on Schmitt trigger, it is characterised in that：
The small-signal termination power, passes through coupled capacitor C by the small-signal that prime sensor exports1It is fed to schmidt trigger
Device input terminal.
3. the small-signal input square-wave generator according to claim 1 based on Schmitt trigger, it is characterised in that：
The feedback circuit, trigger output terminal signal level by R2/C2It is average, and feed back to Schmitt trigger input terminal.
4. the small-signal input square-wave generator according to claim 1 based on Schmitt trigger, it is characterised in that：
The DC bias circuit, passes through potentiometer P by 15V direct current supplys voltage1And capacitor C2Apply one to trigger input terminal
A DC offset voltage UZ。
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201721228367.4U CN207304507U (en) | 2017-09-24 | 2017-09-24 | Small-signal input square-wave generator based on Schmitt trigger |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201721228367.4U CN207304507U (en) | 2017-09-24 | 2017-09-24 | Small-signal input square-wave generator based on Schmitt trigger |
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| CN207304507U true CN207304507U (en) | 2018-05-01 |
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| CN201721228367.4U Expired - Fee Related CN207304507U (en) | 2017-09-24 | 2017-09-24 | Small-signal input square-wave generator based on Schmitt trigger |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111028805A (en) * | 2019-12-20 | 2020-04-17 | 中北大学 | Liquid crystal driving method based on inverter circuit |
-
2017
- 2017-09-24 CN CN201721228367.4U patent/CN207304507U/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111028805A (en) * | 2019-12-20 | 2020-04-17 | 中北大学 | Liquid crystal driving method based on inverter circuit |
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