CN100423452C - D/A converting circuit and method for realizing D/A converting - Google Patents
D/A converting circuit and method for realizing D/A converting Download PDFInfo
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- CN100423452C CN100423452C CNB031559387A CN03155938A CN100423452C CN 100423452 C CN100423452 C CN 100423452C CN B031559387 A CNB031559387 A CN B031559387A CN 03155938 A CN03155938 A CN 03155938A CN 100423452 C CN100423452 C CN 100423452C
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Abstract
The present invention discloses an implement method for a D/A converting circuit and D/A conversion. The circuit comprises a microprocessor and a single-channel PWM D/A converting circuit composed of discrete components, wherein the D/A converting circuit comprises a zero compensating circuit, and the accuracy of the entire circuit is enhanced. The microprocessor can be an SCM of low price and the circuit mainly replaces expensive D/A chips with the discrete components, which greatly reduces cost. Meanwhile, the implement method of D/A conversion disclosed by the present invention uses the SCM of low cost to realize multi-channel PWM signal output so that the simultaneous conversion of multi-channel D/A is completed and the effect of outputting many points is achieved.
Description
Technical field
The present invention relates to the method for a kind of D/A (D/A) change-over circuit and a kind of D/A of realization conversion, particularly relate to the D/A change-over circuit of a kind of employing pulse-width modulation (PWM) technology and realize the method that D/A changes.
Background technology
The D/A change-over circuit is widely used in the control system and instrument and meter in the automation control industry, and its realizes the conversion of digital signal to analog signal.It is converted to analog signal output with control signal set point (being digital signal), be used to drive various valves, frequency converter, in-situ transducer and other instrument and meter of controlling by analog signal, thereby realize control various field control systems and instrument and meter.
Present D/A change-over circuit mainly contains two kinds, and a kind of is D/A change-over circuit based on the D/A chip, and this circuit exists following deficiency: (1) D/A chip price height; (2) because the signal that transmits in the circuit is a high-speed digital signal, be subjected to the interference of external noise signal easily; (3) in the D/A chip, because a plurality of D/A translated channel is packaged together the very difficult isolation that realizes preferably between the path, therefore, if realize the better isolation between the signal of a plurality of path output points, need to increase in addition buffer circuit, thereby cause the increase of technical costs and material cost.
Second kind of D/A change-over circuit is based on PWM (Pulse Width Modulation, pulse width modulation) D/A change-over circuit, the microprocessor (as Intel8098 etc.) that this circuit utilization has a PWM path is regulated the duty ratio of pwm signal, and (duty ratio is under the fixing situation of pulse period, the width of high level shared ratio in the whole cycle), then convert pwm signal to analog signal linearly.In sort circuit,, cause the cost of entire circuit also higher because it is higher to have the microprocessor price of PWM path.If adopt price comparison low as the MC1-51 series monolithic, can only handle the D/A conversion of a path usually, when handled D/A path more for a long time, need to adopt a plurality of single-chip microcomputers, this also increases the cost of D/A change-over circuit inevitably.
Summary of the invention
The object of the present invention is to provide the low D/A change-over circuit of multipath D/A conversion and the method that realizes the D/A conversion of also carrying out of a kind of cost, use foregoing circuit or method to have higher D/A conversion accuracy, and antijamming capability is strong, the reliability height.
A kind of D/A change-over circuit comprises:
At least one unipath PWM D/A change-over circuit;
Microprocessor, its input receives the digital signal of each path, its different output connects described each unipath PWM D/A change-over circuit respectively, be used for digital signal according to each path of receiving calculate a PWM in the cycle high level of each path hold time, and the zero-time and the low level zero-time of the high level of definite each path PWMD/A change-over circuit, utilize timer to produce the pwm signal of exporting to each path PWM D/A change-over circuit, output to corresponding unipath PWM D/A change-over circuit realization D/A conversion simultaneously thereby the digital signal of each path that will receive converts the pwm signal of corresponding path to.
Described unipath PWM D/A change-over circuit comprises: optical coupling isolation circuit, its input connect the corresponding output of described microprocessor, be used for isolating noise reduction process with receiving pwm signal, and this pwm signal is converted to the voltage-type pwm signal; Shaping circuit, its input connects the output of described optical coupling isolation circuit, is used for that the voltage-type pwm signal is carried out shaping and handles; Filter circuit, its input connects the output of described shaping circuit, is used for the voltage-type pwm signal is carried out filtering, obtains a stable voltage signal; The V/I change-over circuit is used for and will converts analog current signal and output to through the filter circuit voltage signal processed, realizes the conversion of digital quantity to analog quantity.
Described unipath PWM D/A change-over circuit also comprises the feedback circuit that connects the V/I change-over circuit, this feedback circuit comprises feed resistance and load, described load one end connects the output of V/I change-over circuit, the other end connects an end of feedback resistance, the other end of described feedback resistance connects the feedback end of described V/I change-over circuit, be used for the feedback end that current signal with output loop changes into voltage signal and outputs to described V/I change-over circuit, realize the automatic adjusting of V/I change-over circuit.
Described unipath PWM D/A change-over circuit also comprises the zero compensation circuit, its output connects described feedback circuit, be used to raise the zero point of the analog current signal of V/I change-over circuit output, remove the relatively poor part of precision in the whole output area, to improve the precision of circuit.
Described zero compensation circuit comprises field effect transistor and adjusting resistance, and wherein, the output of described field effect transistor is connected to the input of feedback resistance, and the two ends of regulating resistance connect the control end and the output of field effect transistor respectively.
Described V/I change-over circuit comprises operational amplifier and field effect transistor, the positive terminal of described operational amplifier is used to receive the voltage signal of described filter circuit output, the end of oppisite phase of described operational amplifier is used to receive the voltage signal of described feedback resistance feedback, the output of operational amplifier connects the control end of field effect transistor, the anode of field effect transistor connects load resistance, and negative terminal connects described feedback resistance.
Described unipath PWM D/A change-over circuit also comprises voltage stabilizing circuit, and the input of described voltage stabilizing circuit connects described optical coupling isolation circuit, and its output connects described shaping circuit, is used to change the size of the voltage of pwm signal to needs.
A kind of method of changing based on the D/A of above-mentioned D/A change-over circuit,
(1) microprocessor converts the multipath digital signal that receives to corresponding pwm signal and outputs to respectively in the PWM D/A change-over circuit of corresponding unipath; Wherein microprocessor carries out following processing operation at each PWM in the cycle:
(1-1) input of microprocessor receives the digital signal of each path;
(1-2) microprocessor calculate a PWM in the cycle high level of each path hold time;
(1-3) the high level zero-time of setting first path is determined the zero-time and the low level zero-time of the high level of follow-up path PWMD/A change-over circuit with this;
(1-4) utilize the timer of microprocessor to produce the pwm signal of every path PWM D/A change-over circuit;
(2) described each unipath PWM D/A change-over circuit converts the pwm signal that receives to analog signal.
Step (1-4) further comprises:
A:, arrange according to time order and function with the zero-time and the low level zero-time of all high level of all paths;
B: calculate adjacent twice time interval;
C: the output pin state of the correspondence of the above-mentioned time interval and a back zero-time is stored;
D: timer produces the pwm signal of every path PWM D/A change-over circuit.
Produce the maximum time of interrupting interval greater than timer each time among the above-mentioned steps b.
The method of using above-mentioned disclosed D/A change-over circuit and realizing the D/A conversion can reach following remarkable result.
(1) whole D/A change-over circuit can adopt cheaply microprocessor and by the pwm circuit D/A change-over circuit that discrete component is formed, finish multipath mould/number conversion, has reduced technical costs and material cost;
(2) in the D/A change-over circuit, increase the zero compensation circuit, removed the relatively poor part of output accuracy, improved the precision of whole D/A conversion;
(3) because the PWM D/A change-over circuit of each path is not packaged together, independently finish the D/A conversion,, improved the antijamming capability of whole PWM D/A change-over circuit greatly so the interference between the output point of each path reduces.
Description of drawings
Fig. 1 is the block diagram of D/A change-over circuit of the present invention.
Fig. 2 is the circuit diagram of an embodiment of D/A change-over circuit of the present invention.
Fig. 3 is the D/A flow path switch figure in a PWM cycle.
Fig. 4 determines the flow chart of the jumping moment of each path for being example with 4 paths.
How Fig. 5 passes through the timer flow chart of output pwm signal simultaneously.
Fig. 6 realizes the realization schematic diagram of 4 road pwm signals output for microprocessor.
Embodiment
D/A change-over circuit of the present invention comprises: at least one unipath PWM D/A change-over circuit 10 and microprocessor 1.The input of microprocessor 1 is used for the digital signal that order receives every path, its different output is connected with each unipath PWM D/A change-over circuit 10 respectively, this microprocessor be used to calculate a PWM in the cycle high level of each path hold time, determine the zero-time and the low level zero-time of the high level of each path, utilize the timer of microprocessor to produce the pwm signal of the PWM D/A change-over circuit that outputs to each path, realize the D/A conversion thereby each path numeral conversion of signals that will receive becomes the pwm signal of corresponding path to output to corresponding unipath PWM D/A change-over circuit.
See also Fig. 1, be the block diagram of D/A change-over circuit of the present invention.This D/A change-over circuit 100 comprises microprocessor 1 and at least one single channel PWM D/A change-over circuit 10, and single channel PWMD/A change-over circuit 10 comprises:
Optical coupling isolation circuit 2, its input connect the output of microprocessor 1 correspondence, are used for the pwm signal that receives is isolated noise reduction process, and this pwm signal is changed at the voltage-type pwm signal;
V/I change-over circuit 5, its input connects filter circuit 4, is used for converting analog current signal and output to through filter circuit 4 voltage signal processed, realizes the conversion of digital signal to analog signal.
Fig. 2 is the circuit diagram of an embodiment of D/A change-over circuit of the present invention.See also Fig. 2, optical coupling isolation circuit 2 comprises two current-limiting resistances and a diode, and optocoupler can be selected the low speed optocoupler for use.The selection of current-limiting resistance mainly is a current transfer ratio of considering optocoupler, can be in the time of making the optocoupler conducting fully or degree of depth saturation condition, so that the low-voltage of output signal is low as far as possible.The use of diode is when guaranteeing the optocoupler conducting, and the signal voltage that outputs to subsequent conditioning circuit can be 0.Voltage stabilizing circuit 9 comprises voltage reference triode and a shunt resistance.This shunt resistance is in order to make that voltage stabilizing circuit 9 can fast and stable.Shaping circuit 3 can use operational amplifier or comparator to realize the stable and shaping of signal, considers to reduce cost and reduce circuit board space, also can use the two-way operational amplifier.If the pwm signal frequency is lower, can use analog switch to realize signal shaping.Filter circuit 4 comprises secondary RC filtering, and the selection of filter constant can be according to the cycle decision of pwm signal, and the filter constant of general secondary all is chosen as 10 times of pwm signal cycle.V/I change-over circuit 5 comprises an operational amplifier 51 and a metal-oxide-semiconductor 52.The positive terminal of operational amplifier 51 be used to the to accept filter voltage signal of output of circuit 4, the end of oppisite phase of operational amplifier 51 is used to receive the voltage signal of feedback resistance 8 feedbacks, the output of operational amplifier 51 connects the control end of field effect transistor 52, the anode of field effect transistor 52 connects load resistance 6, and negative terminal connects feedback resistance 8.Operational amplifier 51 is used to realize the automatic adjusting of V/I change-over circuit 5, and operational amplifier 51 can use with shaping circuit 3 in identical operational amplifier, field effect transistor 52 can adopt metal-oxide-semiconductor to be responsible for the voltage-type pwm signal of operational amplifier 51 output is converted to current analog signal.
Zero compensation circuit 7 comprises a field effect transistor 72 and an adjusting resistance 71, the output of field effect transistor 72 is connected to the input of feedback resistance 8, the two ends of regulating resistance 71 connect the control end and the output of field effect transistor 72 respectively, be used to regulate the electric current that flows through field effect transistor 72, the size of control zero compensation, in Fig. 2, field effect transistor 72 adopts metal-oxide-semiconductor.Because when the input voltage of operational amplifier 51 reaches certain value, output loop just has electric current, raise the zero point of the analog quantity of V/I change-over circuit 5 outputs so adopt zero compensation circuit 7, eliminate the relatively poor part of precision in the D/A change-over circuit 100, improved the output accuracy of whole D/A change-over circuit 100.What feedback resistance 8 used is precision resistance, and this is in order to guarantee the precision of feedback signal.
In addition, the power pack of this circuit can adopt power supply circuits 12 as shown in FIG., uses the DC/DC module to realize a some isolation, perhaps can be according to actual conditions, and direct external power supply.
More than disclosed circuit diagram, only, be not limited only to this for a specific embodiment in the D/A chip of the present invention, those skilled in the art can think equivalence change, all belong to protection range of the present invention.
The invention also discloses method based on the realization D/A conversion of above-mentioned D/A change-over circuit.
S10: microprocessor converts the multipath digital signal that receives to corresponding pwm signal and outputs to respectively in the corresponding single channel PWM D/A change-over circuit; Wherein microprocessor be with a PWM cycle be processing unit, each PWM in the cycle treatment step of microprocessor comprise:
S110: the input of microprocessor receives the digital signal of each path, and promptly order receives the set point of the control signal of each path;
S120: calculate a PWM period T
PInterior high level is held time T
PBe the output signal time that (rising edge or trailing edge) experienced to second same edge edge from first edge.On general, the high level zero-time that PWM cycle is first path is to the high level zero-time of next first path.Simply introducing the control signal set point below is how to convert the value that high level is kept signal to.As: the scope of control signal set point is 0-1000, hope corresponding simulating electric current after the conversion of D/A change-over circuit is 0-20mA, the output current of pwm signal duty ratio 5%-95% correspondence is 0-20mA in the side circuit, suppose that the timer work period is 1uS, the cycle of pwm signal is 10mS (10000uS).Duty ratio is 5% o'clock so, and it is 10000 * 5%=500uS that high level is held time; When duty ratio was 95%, it was 10000 * 95%=9500uS that high level is held time.When changing, when set point=100, then high level is held time=(100/1000) * (9500-500)+500=1400uS; When set point=500, then high level is held time=(500/1000) * (9500-500)+500=5000uS; When set point=900, then high level is held time=(900/1000) * (9500-500)+500=8600uS, the above-mentioned a kind of control signal set point (digital signal) that discloses is how to calculate the method that high level is held time, and the control signal set point of each path that can also will receive by another kind of method converts to correspondingly holds time at the high level of a pwm signal in the cycle.Y=KX+B, X is the control signal set point, Y holds time for corresponding high level, parameter K, X can measure in advance, as the input control signal set point is 100, it is 1400 timer work periods that corresponding high level is held time, and set point is that 900 corresponding high level hold time is 8600 timer work periods, according to two input values, obtain two output valves respectively, 1400=100*K+B, 8600=K*900+B obtains K=9, B=500, a given afterwards control signal set point obtains corresponding high level according to y=9x+500 and holds time;
S130: determine the zero-time of each path high level and low level zero-time (i.e. bound-time from the low level to the high level, from high level to low level bound-time), see also Fig. 4, with 4 paths is example, 2 saltus steps of the output state on each road, from low to high and from high to low promptly, therefore 4 the road always have 8 saltus steps.Describe twice jumping moment that calculates in each path in detail;
S210: set first via pwm signal high level zero-time, it is the beginning in a PWM cycle, calculates first via pwm signal low level zero-time according to the pwm signal after the conversion;
S220: the high level jumping moment of determining the second road pwm signal, guarantee any saltus step of the second road path and the first via any saltus step produce the maximum time of interrupting interval greater than timer, and calculate alternate path pwm signal low level zero-time according to the pwm signal after calculating;
S230: the high level jumping moment of determining the Third Road pwm signal, the any saltus step that guarantees the Third Road path produces the maximum time of interrupting with any saltus step of preceding two-way interval greater than timer, and calculates Third Road pwm signal low level zero-time according to the pwm signal after changing;
S240: the high level jumping moment of determining the four road pwm signal, guarantee any saltus step of the four road path and first three road any saltus step produce the maximum time of interrupting interval greater than timer, and calculate four-way road pwm signal low level zero-time according to the pwm signal after the conversion;
The pwm signal that S140, timer produce each path outputs to corresponding unipath PWMD/A change-over circuit, and concrete steps are as follows:
S310: all jumping moments of all paths being arranged according to time sequencing, calculated the time interval of adjacent twice saltus step, see also Fig. 6, is example with 4 paths, T
R1Be the jumping moment first time of first path, from T
R1To next T
R1Be a PWM cycle, T
R2, T
R3, T
R4Be respectively the jumping moment first time on alternate path, the 3rd path, four-way road, T
F1, T
F2, T
F3, T
F4Be respectively the jumping moment second time on first path, alternate path, the 3rd path and four-way road, according to time sequencing it sorted: T
R1, T
R2, T
F1, T
F2, T
R3, T
R4, T
F3, T
F4, calculate time interval t1, t2, t3, t4, t5, t6, t7, the t8 of adjacent twice saltus step.
S320: the output pin state of the above-mentioned time interval and a back saltus step correspondence is stored;
S330: give the time interval of saltus step next time when jumping moment arrives each time to timer, change the output state of respective channels simultaneously, finish the effect that a plurality of paths are exported the PMW signal simultaneously;
S20: each single channel PWM D/A change-over circuit converts the pwm signal that receives to analog current signal, thereby realizes the conversion of data volume to analog quantity.
More than disclosed be several specific embodiment of the present invention, protection scope of the present invention is based on claim.
Claims (10)
1. a D/A change-over circuit is characterized in that, comprising:
At least one unipath PWM D/A change-over circuit;
Microprocessor, its input receives the digital signal of each path, its different output connects described each unipath PWM D/A change-over circuit respectively, be used for digital signal according to each path of receiving calculate a PWM in the cycle high level of each path hold time, and the zero-time and the low level zero-time of the high level of definite each path PWM D/A change-over circuit, utilize timer to produce the pwm signal of exporting to each path PWM D/A change-over circuit, output to corresponding unipath PWM D/A change-over circuit realization D/A conversion simultaneously thereby the digital signal of each path that will receive converts the pwm signal of corresponding path to.
2. D/A change-over circuit as claimed in claim 1 is characterized in that,
Described unipath PWM D/A change-over circuit comprises:
Optical coupling isolation circuit, its input connect the corresponding output of described microprocessor, be used for isolating noise reduction process with receiving pwm signal, and this pwm signal is converted to the voltage-type pwm signal;
Shaping circuit, its input connects the output of described optical coupling isolation circuit, is used for that the voltage-type pwm signal is carried out shaping and handles;
Filter circuit, its input connects the output of described shaping circuit, is used for the voltage-type pwm signal is carried out filtering, obtains a stable voltage signal;
The V/I change-over circuit is used for and will converts analog current signal and output to through the filter circuit voltage signal processed, realizes the conversion of digital quantity to analog quantity.
3. D/A change-over circuit as claimed in claim 2, it is characterized in that, described unipath PWMD/A change-over circuit also comprises the feedback circuit that connects the V/I change-over circuit, this feedback circuit comprises feed resistance and load, described load one end connects the output of V/I change-over circuit, the other end connects an end of feedback resistance, the other end of described feedback resistance connects the feedback end of described V/I change-over circuit, be used for the feedback end that current signal with output loop changes into voltage signal and outputs to described V/I change-over circuit, realize the automatic adjusting of V/I change-over circuit.
4. D/A change-over circuit as claimed in claim 3, its feature in, described unipath PWM D/A change-over circuit also comprises the zero compensation circuit, its output connects described feedback circuit, be used to raise the zero point of the analog current signal of V/I change-over circuit output, remove the relatively poor part of precision in the whole output area, to improve the precision of circuit.
5. D/A change-over circuit as claimed in claim 4, it is characterized in that described zero compensation circuit comprises field effect transistor and adjusting resistance, wherein, the output of described field effect transistor is connected to the input of feedback resistance, and the two ends of regulating resistance connect the control end and the output of field effect transistor respectively.
6. D/A change-over circuit as claimed in claim 3, it is characterized in that, described V/I change-over circuit comprises operational amplifier and field effect transistor, the positive terminal of described operational amplifier is used to receive the voltage signal of described filter circuit output, the end of oppisite phase of described operational amplifier is used to receive the voltage signal of described feedback resistance feedback, the output of operational amplifier connects the control end of field effect transistor, and the anode of field effect transistor connects load resistance, and negative terminal connects described feedback resistance.
7. D/A change-over circuit as claimed in claim 2, it is characterized in that, described unipath PWMD/A change-over circuit also comprises voltage stabilizing circuit, the input of described voltage stabilizing circuit connects described optical coupling isolation circuit, its output connects described shaping circuit, is used to change the size of the voltage of pwm signal to needs.
8. method based on the realization D/A of claim 1 conversion is characterized in that comprising:
(1) microprocessor converts the multipath digital signal that receives to corresponding pwm signal and outputs to respectively in the PWM D/A change-over circuit of corresponding unipath; Wherein microprocessor carries out following processing operation at each PWM in the cycle:
(1-1) input of microprocessor receives the digital signal of each path;
(1-2) microprocessor calculate a PWM in the cycle high level of each path hold time;
(1-3) the high level zero-time of setting first path is determined the zero-time and the low level zero-time of the high level of follow-up path PWMD/A change-over circuit with this;
(1-4) utilize the timer of microprocessor to produce the pwm signal of every path PWM D/A change-over circuit;
(2) described each unipath PWM D/A change-over circuit converts the pwm signal that receives to analog signal.
9. the method for realization D/A as claimed in claim 8 conversion is characterized in that step (1-4) further comprises:
A:, arrange according to time order and function with the zero-time and the low level zero-time of all high level of all paths;
B: calculate adjacent twice time interval;
C: the output pin state of the correspondence of the above-mentioned time interval and a back zero-time is stored;
D: timer produces the pwm signal of every path PWM D/A change-over circuit.
10. the method for realization D/A as claimed in claim 9 conversion is characterized in that, produces the maximum time of interrupting interval greater than timer each time among the above-mentioned steps b.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101064513B (en) * | 2006-04-25 | 2010-06-09 | 艾默生网络能源系统有限公司 | Digital-to-analog conversion circuit and conversion method |
| DE102010040130A1 (en) * | 2010-09-02 | 2012-03-08 | Robert Bosch Gmbh | Timer module |
| CN102207740A (en) * | 2011-03-30 | 2011-10-05 | 河海大学常州校区 | Isolated multipath 4-20mA-current signal output circuit |
| CN104022772B (en) * | 2013-12-06 | 2017-06-09 | 深圳市伟创电气有限公司 | Can be from zeroing closed loop analog output method and circuit |
| CN105978572A (en) * | 2016-04-29 | 2016-09-28 | 宁波帝洲自动化科技有限公司 | High-precision digital to analog conversion circuit based on PWM |
| CN106941354B (en) * | 2017-04-17 | 2020-10-02 | 北京机械设备研究所 | Hardware circuit correction method based on mathematical fitting |
| CN107979374A (en) * | 2017-11-24 | 2018-05-01 | 威创集团股份有限公司 | Signaling conversion circuit |
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| JPS62198225A (en) * | 1986-02-26 | 1987-09-01 | Sanyo Electric Co Ltd | Digital-analog converter |
| JP2001028544A (en) * | 1999-07-12 | 2001-01-30 | Yokogawa Electric Corp | Multichannel pwm digital/analog converter |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPS62198225A (en) * | 1986-02-26 | 1987-09-01 | Sanyo Electric Co Ltd | Digital-analog converter |
| JP2001028544A (en) * | 1999-07-12 | 2001-01-30 | Yokogawa Electric Corp | Multichannel pwm digital/analog converter |
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| 脉冲计数调制式数/模转换器的设计. 隋青美.自动化仪表，第21卷第6期. 2000 |
| 脉冲计数调制式数/模转换器的设计. 隋青美.自动化仪表，第21卷第6期. 2000 * |
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