CN108227563A - A kind of method that pwm signal is generated by oscillation - Google Patents
A kind of method that pwm signal is generated by oscillation Download PDFInfo
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- CN108227563A CN108227563A CN201711323186.4A CN201711323186A CN108227563A CN 108227563 A CN108227563 A CN 108227563A CN 201711323186 A CN201711323186 A CN 201711323186A CN 108227563 A CN108227563 A CN 108227563A
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- G—PHYSICS
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- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B19/00—Programme-control systems
- G05B19/02—Programme-control systems electric
- G05B19/04—Programme control other than numerical control, i.e. in sequence controllers or logic controllers
- G05B19/042—Programme control other than numerical control, i.e. in sequence controllers or logic controllers using digital processors
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B2219/00—Program-control systems
- G05B2219/20—Pc systems
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- G05B2219/2609—Process control
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Abstract
Present invention is disclosed a kind of methods that pwm signal is generated by oscillation, include the following steps：A hysteresis loop comparator is constructed in pwm signal control system, hysteresis loop comparator includes an input, an output, and inside includes two activation threshold values of high threshold values and low valve valve, high level, low level output are carried out compared with threshold values by input value；A first-order system module is constructed, the time constant of transition is T；Hysteresis loop comparator is attached to form oscillation by the form of feedback with first-order system module.The present invention generates the way of output of pwm signal there is no delay, high level or low level duration can be increased or decreased by changing high threshold and Low threshold at any time, so as to change the duty ratio of output pwm signal.First-order system transient process is unrelated with total time, only with counting period time correlation, and its exponent arithmetic part can shift to an earlier date operation completion directly use, substantially increase operation efficiency.
Description
Technical field
The present invention relates to a kind of methods that pwm signal is generated by oscillation, belong to the technical field of controller output control.
Background technology
In controller field, controlled object is largely analog signal.Although the signal can pass through the side of simulation
Formula is controlled, but it is not a kind of very good control mode, and analog circuit is difficult to adjust easily with time drift
Solution, but also it is especially sensitive to noise, any disturbance all may cause big influence to output.But if pass through digital side
Formula goes control analog signal that can then solve the above problems, and more convenient for the realization of microprocessor.Pulse width is modulated
Using the numeral output of microprocessor come a kind of very effective technology controlled analog circuit, it is widely used in from survey
Amount is communicated into many fields of power control and transformation.
PWM is a kind of to the digitally coded method of analog signal level progress.The duty ratio of square wave is modulated for one
The level of a physical simulation signal is encoded, and at given any moment, the direct current supply of full amplitude only has 0 (nothing) and 1
(having) two states.
There are one important conclusions in sampled-data control theory：The equal and variform burst pulse of momentum is added in used
When in property link, effect is essentially identical.Momentum refers to the area of burst pulse.The essentially identical the output phase Ying Bo for referring to link of effect
Shape is essentially identical.If each output waveform is analyzed with Fourier transformation, low-frequency range is very close, only slightly has in high band
Difference.Above-mentioned principle is referred to as area equivalent principle, is the most important theories basis of PWM control technologies.According to the theory, work as needs
When generating a certain analog signals, it is only necessary to the pulse signal of area equation is added on inertial element, by a system
The width of row pulse is modulated, and carrys out the waveform needed for equivalent acquisition (comprising shape and amplitude).As shown in fig. 7, with a system
The not wide pulse of row constant amplitude replaces a half-sinusoid, and half-sinusoid N deciles regard N number of connected pulse train, width as
Equal but amplitude differs；Above-mentioned pulse is replaced with rectangular pulse, the rectangular pulse constant amplitude is not wide, midpoint and above-mentioned pulse weight
It closes, area (momentum) is equal, and width is changed by sinusoidal rule.The pwm signal can then generate pair after an inertial element
The half-sinusoid answered.Pulse sequence frequency is higher, then passes through the closer former modulation waveform of the waveform generated after inertial element.
Principles above shows that (such as motor, liquid can be applied to when the system being applied to has the system of inertial element
Body etc.), the control of analog signal can be substituted by way of digital signal.Output control is carried out by digital form, it can be with
The cost and power consumption of system is greatly lowered, in addition, many microcontrollers and DSP contain PWM controller on chip,
This makes digital control to become to be more prone to.
To generate pwm pulse signal using hardware timer in digital Control Technology, timer repeat according to
PWM cycle is counted, and comparand register is for keeping modulation value, and the value in comparand register is compared with timer count value
Compared with when two value matchings, saltus step occurs for PWM outputs.The frequency of PWM is determined by the counting period of timer, and the duty of PWM
Than then being codetermined by the value for counting period and comparand register of timer.Fig. 8 and Fig. 9 describes two kinds of PWM producing methods.
Two kinds of generating modes are all relatively to generate pwm signal by count value and fiducial value.Compare when count value is less than
Low level is exported during value, high level is exported when count value is more than count value, output can also be negated as needed.It is all when counting
When phase changes, the frequency of output pwm signal accordingly changes, and when fiducial value size changes, the duty ratio for exporting PWM also changes therewith
Become.The difference of the two is only embodied on counting mode.
In the controls, the major function of controller is exactly the value control by controlled variable in given range.Control
Device processed can calculate the value of controlled volume and the difference of set-point, and go out to control the value of signal according to mathematic interpolation, then operation and control
Mechanism drives controlled variable, it is made to be acted to the direction reduced with set-point difference, until reaching set-point.Assuming that controller
Controlling cycle is 50ms, i.e., controller can acquire the value of a controlled volume every 50ms, and calculate the value of current controlled volume with to
The difference of definite value so as to calculate the value of control signal and output, controls the value of signal not change in next 50ms.
After 50ms, controller can repeat the above process, and calculate new difference, calculate new control signal and export.From upper
The action time that the process of stating can be seen that each control signal is the time of the controlling cycle of controller, and each period starts
When can calculate the value of a new control signal.And it is seen that not considering chip calculating speed and Acquisition Error etc.
During actual conditions, the period of controller control is higher, then the real-time controlled is also better.
Under normal circumstances, the counting period and fiducial value that pwm signal generation needs are that software calculates completion, and counting in advance
Related register is written when numerical value restarts, for generating the pwm signal of next cycle, as shown in Figure 10.
Further, it is exactly after a complete PWM waveform is exported, counts the period and arriving for fiducial value ability updates.Reason
The PWM signal frequency exported in the case of thinking is higher, then it is applied to effect on inertial element closer to analog output, still
Under normal conditions, control system major part exterior operator is mechanical part, can not be rapidly performed by switching, in this way
Can greatly shorten the service life of executing agency.And executing agency has the minimum of oneself to open and close time, pwm signal
Frequency is excessively high may to make executing agency have little time to respond at all.Therefore under many application scenarios, controller is to pass through frequency
Exterior operator is controlled than relatively low pwm signal.
Assuming that the execution frequency requirement of the exterior operator of certain control system control is 2Hz, i.e. the period of pwm signal is
500ms, and control period of chip interior acquisition process as 50ms, i.e., it can calculate a PWM duty cycle and frequency per 50ms
Information, operational process is as shown in figure 11.
As seen from Figure 11, although control chip can calculate a PWM information per 50ms, due to PWM's
Period is 500ms, therefore the PWM information only calculated for the last time can just be exported, that is, the PWM in this 500ms
Generation module does not have any response to the result of calculation for controlling chip.Therefore this way of output is for pwm signal frequency
The slow scene of rate can cause greatly to delay, and the system for needing quick response cannot be met the requirements.
From the above, it can be seen that for the current PWM way of outputs, control the output of signal can not be with
The controlling cycle of controller synchronizes, but controlling cycle is fast, and control signal output is slow, and the value that signal is controlled to export has centainly
Uncertainty.If control signal update, difference is exactly in a special state, and (such as this time difference value is exactly in one
Spike), then the value of control signal generated at this time will continue the entire PWM output period, and cannot correct, and seriously affect and be
System stability.
Invention content
Present invention aim to address above-mentioned the deficiencies in the prior art, provide a kind of side that pwm signal is generated by oscillation
Method.
In order to achieve the above object, the technical solution adopted in the present invention is：
A kind of method that pwm signal is generated by oscillation, includes the following steps：
Step a, constructs a hysteresis loop comparator in pwm signal control system, and the hysteresis loop comparator is defeated comprising one
Entering, an output, inside includes two activation threshold values of high threshold values and low valve valve,
When the value of input is more than high threshold, hysteresis loop comparator output low level, when input value is less than Low threshold, hysteresis
Comparator exports high level, if input value, between high threshold and Low threshold, hysteresis loop comparator keeps the output of front not
Become；
Step b constructs a first-order system module, and the first-order system module includes an input and an output, interior
Portion includes a time constant T, can be in the form of first-order system to input value mistake by the output valve of the first-order system module
It crosses, the time constant of transition is T；
Step c, hysteresis loop comparator are attached to form oscillation by the form of feedback with first-order system module.
Preferably, the oscillation step of the step c is as follows：
The high threshold of the hysteresis loop comparator is TH2, Low threshold TL2, TH2, TL2 are between 0 and 1, first-order system
It is 0 that the time constant of module, which is T and initially exports,；
Since the output of first-order system module is 0, less than the Low threshold TL2 of hysteresis loop comparator, therefore hysteresis loop comparator
It is 1 to export, i.e. the input value of first-order system becomes 1, and the output of first-order system module at this time then can be according to one that time constant is T
Rank characteristic is to 1 transition；
When the output of first-order system module is between TH2, TL2, due to the characteristic of hysteresis loop comparator, output can't
It changes, therefore the output of first-order system module will continue to 1 transition；
When the output when first-order system module is more than TH2, the output of hysteresis loop comparator at this time can then suddenly become 0,
I.e. the output of first-order system module at this time can be changed to 0 transition；
When the output of first-order system module is less than TL2, the output of hysteresis loop comparator can become 1 again, so as to first-order system
The output of module starts, to 1 transition, and so on, to form oscillation.
Preferably, the single order transition step of first-order system module is as follows in the step b：
By the way of recursion,
By above-mentioned formula discretization, and handle,
△ t are time interval,
Wherein, 1-h (n) is the difference of desired value and current time value, and 1-h (n-1) is the difference of desired value and previous moment value,
The ratio of the two is a fixed value related with time interval, and the value of previous moment is interpreted as initial value, obtains formula such as
Under,
Wherein, VdIt is desired value, VsIt is current value, VnIt is the value after the △ t times；
The calculating cycle of control system is fixed, when system is handled, K values is calculated and is preserved, if time interval
For △ t, then
The beneficial effects are mainly as follows：
1. the present invention generates the way of output of pwm signal there is no delay, at any time can be by changing high threshold
Value and Low threshold increase or decrease high level or low level duration, so as to change the duty ratio of output pwm signal.
2. first-order system transient process is unrelated with total time, only with counting period time correlation, and its exponent arithmetic portion
Operation completion can be shifted to an earlier date by, which dividing, directly uses, and substantially increases operation efficiency.
Description of the drawings
Fig. 1 is the structure diagram that oscillation is formed in a kind of this method by oscillation generation pwm signal.
Fig. 2 is the schematic diagram of oscillatory process in a kind of this method that pwm signal is generated by oscillation.
Fig. 3 is hysteresis loop comparator input-output characteristic schematic diagram.
Fig. 4 is first-order system module input-output characteristic schematic diagram.
Fig. 5 is the schematic diagram that output situation is vibrated when pwm signal duty ratio changes.
Fig. 6 is the unit-step nsponse curve schematic diagram of first-order system.
Fig. 7 is pwm signal and its corresponding debugging oscillogram in the prior art.
Fig. 8 is a kind of schematic diagram of pwm signal generation in the prior art.
Fig. 9 is another schematic diagram of pwm signal generation in the prior art.
Figure 10 is to count period and the newer schematic diagram of fiducial value in the prior art.
Figure 11 is to control chip in the prior art to the newer schematic diagram of PWM information.
Specific embodiment
The present invention provides a kind of method that pwm signal is generated by oscillation.Below in conjunction with attached drawing to technical solution of the present invention
It is described in detail, so that it is more readily understood and grasps.
A kind of method that pwm signal is generated by oscillation, constructs a hysteresis loop comparator first, which includes
One input, an output, inside includes two activation threshold values.Its function is the hysteresis ratio when the value of input is more than high threshold
Export low level compared with device, when input value is less than Low threshold, hysteresis loop comparator output high level, if input value between high threshold and
Between Low threshold, then hysteresis loop comparator keeps the output of front constant.Its input-output characteristic is as shown in Figure 3.
As seen from Figure 3, if input value is ascending between Low threshold and high threshold, output is high electricity
Flat, if input value is descending between Low threshold and high threshold, output is low level.
Secondly, a first-order system module is constructed, which includes an input and an output, when inside includes one
Between constant T.Its function is that the output valve of the module can be in the form of first-order system to input value transition, the time constant of transition
For T.Its transient process is as shown in Figure 4.
Curve 1 in Fig. 4 is the unit-step nsponse curve of first-order system, and the process of description is when the input of system is defeated
When going out value all for 0 state, when input becomes 1 from 0 suddenly, the response curve of output.The process that curve 2 describes is when system
When input and output value is all 1 state, when input becomes 0 from 1 suddenly, the response curve of output.The speed of its transient process by
Time constant T is determined.
Hysteresis loop comparator with first-order system module according to the structure of Fig. 1 is combined, then may be constructed an oscillator.
As seen from Figure 1, two modules are attached by the form of feedback, to form oscillation.Its oscillatory process
As shown in Figure 2.
In on the left of Fig. 2, the high threshold of hysteresis loop comparator is TH2, Low threshold TL2, TH2, TL2 are between 0 and 1,
It is 0 that the time constant of first-order system module, which is T and initially exports,.Since the output of first-order system module is 0, less than hysteresis ratio
Compared with the Low threshold TL2 of device, therefore the output of hysteresis loop comparator is 1, i.e. the input value of first-order system becomes 1.First-order system at this time
The output of module then can be according to the first-order characteristics that time constant is T to 1 transition.When first-order system module is exported between TH2, TL2
Between when, due to the characteristic of hysteresis loop comparator, output can't change, therefore the output of first-order system module will continue to
To 1 transition.When the output when first-order system module is more than TH2, the output of hysteresis loop comparator at this time can then suddenly become 0,
I.e. the output of first-order system module at this time can be changed to 0 transition.When the output of first-order system module is less than TL2, hysteresis compares
The output of device can become 1 again, so as to which the output of first-order system module starts, to 1 transition, and so on, to form oscillation.
It is the output of hysteresis loop comparator on the right side of Fig. 2, as can be seen from Figure when the high threshold of hysteresis loop comparator and Low threshold
When different, the signal dutyfactor of output, frequency also differ.According to the characteristic of first-order system, when to during 1 transition, closer to 1
Then the rate of climb is slower, and decrease speed becomes faster, and duty ratio increases, and when to during 0 transition, it is slower closer to 0 decrease speed, on
Lifting speed becomes faster, and duty ratio reduces, i.e. the duty ratio of hysteresis loop comparator output increases with the increase of high threshold and Low threshold.
Therefore it can realize that the pwm signal of different duty exports by setting high threshold and the Low threshold of hysteresis loop comparator.
When the pwm signal duty ratio that control system to be exported is constant, such pwm signal producing method is taken with using
The mode of the generation pwm signal of hardware timer is different without what.But when the pwm signal duty ratio to be exported needs to change
When, then the two will show different output characteristics.
If the pwm signal duty ratio of control system output will at a time change suddenly, using hardware timer
System can then wait for present PWM signal export after the completion of, more New count period and fiducial value, to generate new pwm signal.It is right
Execution can be then instantly available in the system for using the oscillator mode.Add in the corresponding hysteresis loop comparator high threshold of original duty cycle
It is respectively TH2 and TL2 with Low threshold, the high threshold and low threshold of the corresponding hysteresis loop comparator of duty ratio of the pwm signal after change
Value is respectively TH1 and TL1.Then system operation is as shown in Figure 5.
Before the t1 moment, the output valve of first-order system module vibrates between TH2 and TL2, the PWM of hysteresis loop comparator output
Signal is original duty cycle.When at the t1 moment, system will export new pwm signal suddenly, and the value of duty ratio needs to reduce, stagnant
The high threshold and Low threshold for returning comparator are also become by TH2 and TL2 for TH1 and TL1 respectively.It can be with by the characteristic of hysteresis loop comparator
It learns, when the output valve of first-order system module is transitioned into TL2, the output valve of hysteresis loop comparator will not invert, but meeting
It can just be inverted until being transitioned into TL1.It is equivalent to and directly extends the low level time of output signal at this time, i.e. PWM letters
Number duty ratio also reduce.Above-mentioned example is to change duty ratio during oscillation declines, if reducing in uphill process is vibrated
Duty ratio, then transition value can reach TH1 and just invert, be equivalent to and high level switched into low level in advance, believe the PWM of output
Number duty ratio reduces.In terms of the above process, which, at any time can be by changing high threshold there is no delay
High level or low level duration are increased or decreased with Low threshold, so as to change the duty ratio of output pwm signal.This spy
Property has sizable technical advantage in some systems for needing low frequency PWM control signal.
Regard above-mentioned first-order system module and hysteresis loop comparator as an oscillatory system, then the system includes three variable ginsengs
Number, respectively high threshold TH, Low threshold TL, first-order system time constant T.The difference of high threshold TH and Low threshold TL, which determine, shakes
The oscillation amplitude of system is swung, first-order system time constant T determines the hunting speed of oscillatory system.It is realized in the software of the module
In the process, it is fairly simple and very easy realization that transition value and high threshold, Low threshold, which are compared and export, main problem
Concentrate on the realization of first-order system transient process above.
If the input signal of first-order system is unit jump function r (t)=1 (t), corresponding output
By formula (1) as it can be seen that it is 0 that the unit-step response of first-order system, which is an initial value, end is risen to exponential law
The curve of value 1.T is the time constant that time, i.e. first-order system used in 0.632 are risen to from 0, as shown in Figure 6.
Fig. 6 shows that the unit-step response of first-order system is dead-beat response, has following two important features：
1st, pot life constant T removes the numerical value of gauging system output quantity.When t is respectively T, 2T, 3T, during 4T, the value of h (t)
Respectively 0.632,0.865,0.95 and 0.982.
2nd, the slope initial value of response curve is 1/T, and is declined over time
Its transient process is one and the relevant processes of time t it can be seen from formula (2), due to the time through I
Entire control process, can make if this variable of time is introduced into formula software calculate it is relative complex.And its is defeated
Enter value always to change, if if also regarding the change of each input value as an excitation, the excitation can be generated one newly
The function with time correlation.Therefore very big difficulty will obviously be brought, and infeasible to calculating using this way.
We are solved the above problems by the way of recursion herein.
Then by above-mentioned (3) formula discretization, and handle
△ t are time interval.
Formula 4 is further looked at as can be seen that 1-h (n) is the difference of desired value and current time value, 1-h (n-1) is target
The difference of value and previous moment value, the ratio of the two is a fixed value related with time interval.If the value of previous moment is managed
It solves as initial value, then obtains formula (5),
Wherein, VdIt is desired value, VsIt is current value, VnIt is the value after the △ t times.
Therefore, it is known that current value and desired value, it is possible to calculate the value after the △ t times.
It, can be in advance by K value meters when system is handled since the calculating cycle of control system is usually fixed
It calculates and preserves, if time interval is △ t, then
Using above method, then first-order system transient process can be converted to it is unrelated with total time, only and the counting period
The calculation formula of time correlation, and its exponent arithmetic part can shift to an earlier date operation completion and directly use.Mistake entire in this way
Transient just becomes to only remain subtraction and multiplying, substantially increases operation efficiency.And when desired value changes,
Any calculation amount of software will not be increased.
By above description it can be found that a kind of method that pwm signal is generated by oscillation of the present invention, generates pwm signal
The way of output there is no delay, at any time can by change high threshold and Low threshold increase or decrease high level or
The low level duration, so as to change the duty ratio of output pwm signal.First-order system transient process is unrelated with total time, only
With counting period time correlation, and its exponent arithmetic part can shift to an earlier date operation completion directly use, substantially increase
Operation efficiency.
Technical scheme of the present invention is fully described above, it should be noted that specific embodiment party of the invention
Formula is simultaneously not limited by the description set out above, the Spirit Essence of those of ordinary skill in the art according to the present invention structure, method or
All technical solutions that function etc. is formed using equivalents or equivalent transformation, all fall within protection scope of the present invention
Within.
Claims (3)
- A kind of 1. method that pwm signal is generated by oscillation, it is characterised in that include the following steps：Step a, constructs a hysteresis loop comparator in pwm signal control system, and the hysteresis loop comparator includes input, one A output, inside include two activation threshold values of high threshold values and low valve valve,When the value of input is more than high threshold, hysteresis loop comparator output low level, when input value is less than Low threshold, hysteresis compares Device exports high level, if input value, between high threshold and Low threshold, hysteresis loop comparator keeps the output of front constant；Step b, constructs a first-order system module, and the first-order system module includes an input and an output, inside packet Containing a time constant T, by the output valve of the first-order system module can in the form of first-order system to input value transition, The time constant of transition is T；Step c, hysteresis loop comparator are attached to form oscillation by the form of feedback with first-order system module.
- A kind of 2. method that pwm signal is generated by oscillation according to claim 1, it is characterised in that the oscillation of step c Step is as follows：The high threshold of the hysteresis loop comparator is TH2, Low threshold TL2, TH2, TL2 are between 0 and 1, first-order system module Time constant be T and initially output be 0；Since the output of first-order system module is 0, less than the Low threshold TL2 of hysteresis loop comparator, therefore the output of hysteresis loop comparator It is 1, i.e. the input value of first-order system becomes 1, and the output of first-order system module at this time then can be special according to the single order that time constant is T Property is to 1 transition；When the output of first-order system module is between TH2, TL2, due to the characteristic of hysteresis loop comparator, output can't occur Change, therefore the output of first-order system module will continue to 1 transition；Once the output when first-order system module be more than TH2 when, the output of hysteresis loop comparator at this time can then suddenly become 0, i.e., this When first-order system module output can be changed to 0 transition；When the output of first-order system module is less than TL2, the output of hysteresis loop comparator can become 1 again, so as to first-order system module Output start to 1 transition, and so on, form oscillation.
- 3. a kind of method that pwm signal is generated by oscillation according to claim 1, it is characterised in that in the step b The single order transition step of first-order system module is as follows：By the way of recursion,By above-mentioned formula discretization, and handle,△ t are time interval,Wherein, 1-h (n) is the difference of desired value and current time value, and 1-h (n-1) is the difference of desired value and previous moment value, the two Ratio for a fixed value related with time interval, the value of previous moment is interpreted as initial value, it is as follows to obtain formula,Wherein, VdIt is desired value, VsIt is current value, VnIt is the value after the △ t times；The calculating cycle of control system is fixed, when system is handled, K values is calculated and is preserved, if time interval is △ T, then
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| CN103973271A (en) * | 2014-04-28 | 2014-08-06 | 苏州经贸职业技术学院 | Signal generation circuit |
| CN205977764U (en) * | 2016-08-26 | 2017-02-22 | 施洁 | Controlled speed governing circuit of direct current fan |
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- 2017-12-13 CN CN201711323186.4A patent/CN108227563A/en active Pending
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| Publication number | Priority date | Publication date | Assignee | Title |
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| FR2301970A1 (en) * | 1975-02-24 | 1976-09-17 | Sony Corp | SIGNAL AMPLIFIER MODULATED BY PULSES OF VARIABLE DURATION |
| CN1752924A (en) * | 2005-08-18 | 2006-03-29 | 上海微科集成电路有限公司 | Real random number generator based on oscillator |
| CN101275980A (en) * | 2007-12-06 | 2008-10-01 | 上海大学 | Differential capacitance PWM converter |
| CN102938648A (en) * | 2012-10-31 | 2013-02-20 | 上海华兴数字科技有限公司 | Analog quantity output circuit applied to controller of engineering machinery |
| CN103973271A (en) * | 2014-04-28 | 2014-08-06 | 苏州经贸职业技术学院 | Signal generation circuit |
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