CN1822506A - Integrating A/D convertion method and its A/D converter - Google Patents
Integrating A/D convertion method and its A/D converter Download PDFInfo
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Abstract
An integration type A/D converting method includes 11 ) making bidirectional integration to zero voltage V 0 and standard voltage Vb, obtaining count value T0, 12 ) making bidirectional integration to reference voltage V 1 and standard voltage Vb, obtaining count value T1, 13 ) making bidirectional integration to switching voltage Vx and standard voltage Vb, obtaining count value Tx, 14 using formulae Vx = ( V 1- 1- V 0 ) ( Tx - t 0 ) / ( t 1- 1- t 0 ) + V 0 to calculate switching voltage Vx value. Bidirectional integration in Above-mentioned steps includes following steps: 1, to proceed positive direction timing integration to 0 or V 1 or Vx, timing time being the fixed time Td when integrating circuit output voltage passing zero, 2, stopping integration when reaching integration time Td, beginning reversal integration to integrator adopting standard voltage Vb, at the same time counter beginning counting, 3, when integrator output voltage passing zero, generating triggering signal to stop counter counting, respectively obtaining count value T0, T1 or Tx corresponding to voltage V 0, V 1 or Vx. Said invention also discloses A/D converter to realize above-mentioned method.
Description
Technical field
The present invention relates to analog-to-digital conversion (A/D conversion) method, particularly relate to a kind of integration type D conversion method.The invention still further relates to a kind of analog-digital commutator that uses this method.
Background technology
Analog to digital converter (A/D converter) is used for realizing the conversion of simulation (voltage or electric current) signal to digital signal.It is widely used in various digital processing occasions, for example at instrument field, and the digital signal that it becomes computer system to discern the analog-signal transitions of various transducers in scene or transmitter, thus realize monitoring and processing to on-site signal.
Present A/D change-over circuit mainly comprises counter A/D converter, comparison A/D transducer, parallel A/D converter, double integration A/D converter or the like one by one, and wherein double integration A/D converter is to use more a kind of A/D converter.Double integral A/D converter has good interference free performance, is used widely in the slow signal data acquisition of digital voltmeter and industry spot.
Double integration A/D converter is a kind of indirect A/D converter.So-called A/D converter indirectly is the M signal (as becoming time, frequency etc.) that earlier analog signal voltage is transformed to corresponding certain form, and then this M signal is transformed to binary code output.At present, double integration A/D converter generally is the indirect A/D converter of voltage-time (V-T) changing type.
Fig. 1 and Fig. 2 are respectively the schematic diagram of double integration A/D converter composition frame chart and double integration A/D conversion method.
Please referring to Fig. 1, described double integration A/D converter is made up of integrator 11, zero-crossing comparator 12, reference power supply 13, clock 14, control logic circuit 15 and counter 16.
Below in conjunction with Fig. 2, the operation principle of this A/D converter of brief description.
As shown in Figure 2, dual integration A/D conversion method is specifically: at first, control logic circuit 15 is selected circuit 17 by integration, select the input of aanalogvoltage Ui to be converted, 11 couples of these aanalogvoltage Ui forward integration set time T to be converted of integrator (this time of integration is by clock 14 meterings) as integrator 11; Then, described control logic circuit 15 is selected circuit 17 by integration, and the reference voltage U1 of the known voltage value of selection reference power supply 13 outputs carries out reverse integral on integrator 11, is zero up to the output voltage of integrator 11.When carrying out above-mentioned integration, use described counter 16 to count.By comparator 12, can when integrator 11 output voltage zero passages, produce the conversion of high-low level, thereby produce triggering signal, this triggering signal control counter 16 stops counting, obtains a count value, adopts the output of this count value as the A/D conversion.
As shown in Figure 2, because fixedly the time of integration, T was known, corresponding two different voltage A and B have the reverse integral time T 1 and the T2 that are proportional to magnitude of voltage respectively.Adopt formula: U
i=U1*T/T
iJust can calculate the value of aanalogvoltage to be converted, be exactly U corresponding to voltage A
A=U1 * T/T2; B is exactly corresponding to voltage: U
B=U1 * T/T1.
Usually, directly use described set time T and the count value of the reverse integral time digital value after as the A/D conversion.
What above-mentioned double integration A/D change-over circuit responded is the mean value of input signal, and when having the interference signal of stack, interference signal also is with its mean value the A/D transformation result to be exerted an influence, and therefore, dual integration A/D has good interference free performance.
But the conversion accuracy of above-mentioned double integration A/D conversion method is still not high enough, can not fully meet the demands.
At first, said method does not consider that zero-point voltage is to the influence of integral process in the circuit.
In the physical circuit, since the difference of circuit element parameter, output voltage and non-vanishing when making zero input, and this voltage is called zero-point voltage.When the aanalogvoltage to be converted to input carries out integration, also can carry out integration to this zero-point voltage simultaneously, the existence of this zero-point voltage increases the numerical value after the A/D conversion.
Secondly, in the above-mentioned A/D conversion method, at first carry out the forward integration, carry out reverse integral then, the former is that the latter is a capacitor discharge to the electric capacity charging, and the time constant of electric capacity in charge and discharge process is discrepant, and this influences the precision of A/D conversion equally.
Once more, fixedly the time of integration, T adopted the timer metering in the prior art, and the reverse integral time disunity on measurement standard with the counter metering causes error.
Summary of the invention
Shortcoming at double integration A/D conversion regime in the prior art, the invention provides a kind of integration type A/D conversion method, the defective that this method causes conversion accuracy to reduce at zero-point voltage and forward and reverse integration etc. in the prior art, take to remedy accordingly measure, thereby have higher A/D conversion accuracy.The present invention provides a kind of A/D change-over circuit that uses this method simultaneously.
Integration type A/D conversion method provided by the invention comprises:
11) zero-point voltage V0 and normal voltage Vb are carried out two-way integration, obtain count value T0;
12) reference voltage V 1 and normal voltage Vb are carried out two-way integration, obtain count value T1;
13) treat changing voltage Vx and normal voltage Vb carries out two-way integration, obtain count value Tx;
14) use formula Vx=(V1-V0) (Tx-T0)/(T1-T0)+V0 calculates the value of voltage Vx to be converted, with A/D conversion output valve of this value as voltage Vx to be converted.
Preferably, described step 11) comprises:
21) null offset voltage V0 is carried out regularly integration of forward, wherein timing is set time Td, and this timing Td begins to calculate when integrating circuit output voltage zero passage;
22) Td time of integration to null offset voltage V0 arrives, and stops integration, begins to adopt normal voltage Vb to the integrator reverse integral, and unison counter begins counting;
23) when the integrator output voltage zero passage, produce triggering signal, make counter stop counting; Obtain count value T0.
Preferably, described step 12) comprises:
31) reference voltage V 1 is carried out regularly integration of forward, wherein timing is set time Td, and this timing Td begins to calculate when integrating circuit output voltage zero passage;
32) Td time of integration to reference voltage V 1 arrives, and stops integration, begins to adopt normal voltage Vb to the integrator reverse integral, and unison counter begins counting;
33) when the integrator output voltage zero passage, produce triggering signal, make counter stop counting; Obtain count value T1.
Preferably, described step 13) comprises:
41) treat changing voltage Vx and carry out regularly integration of forward, wherein timing is set time Td, and this timing Td begins to calculate when integrating circuit output voltage zero passage;
42) Td time of integration to null offset arrives, and stops integration, begins to adopt normal voltage Vb to the integrator reverse integral, and unison counter begins counting;
43) when the integrator output voltage zero passage, produce triggering signal, make counter stop counting; Obtain count value Tx.
Preferably, described forward integration is opposite with the integration direction of reverse integral, and the forward integration can be to positive voltage direction or negative voltage direction integral, and corresponding, reverse integral is exactly to negative voltage direction or positive voltage direction integral.
Preferably, after the described step 14), can directly return step 13) next one voltage Vx to be converted is carried out the A/D conversion, continue to use T0, the T1 that obtains in step 11), the step 12) this moment.
Preferably, according to the voltage range of described voltage to be converted with its stepping, for certain voltage to be converted, with this grade upper voltage limit ± voltage in 20% scope is as the value of reference voltage V 1.
Preferably, the value of described zero-point voltage V0, reference voltage V 1 obtains by demarcating in advance.
Preferably, described normal voltage Vb is that a galvanic current is pressed.
Integration type A/D conversion equipment provided by the invention comprises control computation unit, multichannel analog signals selection circuit, voltage reference circuit, integrating circuit, comparator, direct current regulation circuit;
Described control computation unit is used for the integral process of described integrator is controlled, and calculates according to the count value that integration obtains, and obtains the A/D transformation result; Described integral process comprises the two-way integration with normal voltage Vb to zero-point voltage V0, reference voltage V 1, voltage Vx to be converted etc., obtains count value T0, T1, Tx respectively; Described according to count value calculate to obtain the A/D transformation result be utilize formula Vx=(V1-V0) (Tx-T0)/(T1-T0)+V0 calculates;
Described voltage reference circuit is used to provide reference voltage V 1;
Described integrating circuit is used for realizing integral process according to the control of described control computation unit; Comprise two-way integration to zero-point voltage V0, reference voltage V 1, voltage Vx to be converted and normal voltage Vb;
Described comparator, be used to receive the output voltage of integrating circuit, and with this voltage and no-voltage comparison, when comparator output is undergone mutation, this jump signal is outputed to described control computation unit as triggering signal, and what beginning when being used for controlling two-way integration forward integrating meter and reverse integral were counted stops;
Described direct current regulation circuit is used to obtain the galvanic current pressure and offers above-mentioned each unit use, comprises providing normal voltage Vb to be used for described two-way integration.
Preferably, described integration type A/D conversion equipment also comprises:
Multichannel analog signals is selected circuit, it has a plurality of inputs, be used to receive a plurality of input signals, comprise voltage Vx to be converted, reference voltage V 1, its address end is used for the receiver address signal, and select corresponding in a plurality of inputs of this address signal one be communicated to output as output signal, this output signal is as the input of described integrator.
Preferably, described integration type A/D conversion equipment also comprises:
Ripple counter is used for the receiver address signal, and this address signal is converted into parallel binary address signal, selects the address signal of the address end of circuit as outputing to described multichannel analog signals.
Preferably, described integration type A/D conversion equipment also comprises:
Optical coupling isolation circuit is used to receive the address signal that described control computation unit is exported, and carries out outputing to described ripple counter after photoelectricity is isolated; And the triggering signal that receives described comparator output, through outputing to the input of described control computation unit after the photoelectricity isolation.
Preferably, described integration type A/D conversion equipment also comprises:
Programmable amplifying circuit, be used to receive described reference voltage, voltage to be converted, and the multiplication factor that receives control computation unit output, according to described multiplication factor, behind described reference voltage, the corresponding multiple of voltage amplification to be converted, as input to described integrator.
Preferably, described integration type A/D conversion equipment also comprises filter circuit, is used to receive the voltage signal after the described amplification of described programmable amplifying circuit output, and after the interference signal in this signal filtered, is re-used as the input of described integrator.
Preferably, described control computation unit is a microprocessor.
Preferably, described voltage reference circuit comprises a standard of precision voltage and several precision resistances; Standard of precision voltage by several precision resistance dividing potential drops after, produce several reference voltages, the value of described reference voltage is near the upper limit of stepping of voltage to be converted ± certain voltage in 20% the scope.
Preferably, described programmable amplifying circuit comprises amplifier, multiway analog switch and resistance; Multiway analog switch and resistance cooperate, and are made of the amplifier of various multiplication factor control computation unit control.
Compared with prior art, the method for above-mentioned double integration A/D conversion has a following advantage:
1, adopted of the influence of the method for zero-point voltage integration measuring and calculating zero-point voltage integral process.
2, different with the common double integrating circuit, the counting process of this circuit is the process that aligns to integration and counts, and has got rid of the situation that common double compares mutually to integrating circuit forward integral counting, reverse integral counting; The difference of having avoided forward integration, reverse integral to exist.
3, directly do not use set time Td to calculate in this method, but usage count value T1 owing to adopt common measurement standard, make the A/D transformation result more accurate.
4, this method is according to the scope of the value of voltage to be converted, be divided into different voltage gears, use the reference voltage V 1 that approaches this grade voltage range upper limit at different voltage gear, use this reference voltage V 1 and zero-point voltage V0 to calculate the value of voltage Vx to be converted, have the effect of linear interpolation.Because the A/D change-over circuit that adopts has good linearty, therefore adopt approach based on linear interpolation can obtain conversion value accurately.The value of the reference voltage U1 that the two-way integration A/D conversion of prior art is only adopted is calculated voltage to be converted, does not have the linear interpolation effect, and its conversion value is accurate not as this method.
5, because the A/D conversion method that this method adopts has higher principle, except precision and stability to voltage reference and divider resistance have certain requirement, other electronic device does not need to adopt high-precision element just can realize higher A/D conversion accuracy in the circuit.In contrast to this, under prior art, to reach identical A/D conversion accuracy, necessary higher grade of service precision electronic device, and the raising of the accuracy class of electronic device can cause increasing substantially of cost.Therefore, the present invention also has cost advantage.
Description of drawings
Fig. 1 is the composition frame chart of the double integration A/D change-over circuit of prior art;
Fig. 2 is the waveform schematic diagram of the double integration A/D change-over circuit operation principle of prior art;
Fig. 3 is the flow chart of first embodiment of the invention;
Fig. 4 is the waveform schematic diagram of the A/D conversion method of first embodiment of the invention;
Fig. 5 is the composition frame chart of the A/D change-over circuit of first embodiment of the invention;
Fig. 6 is the circuit theory diagrams of first embodiment of the invention.
Embodiment
See also Fig. 3, this figure is the flow chart of first embodiment of the invention.See also Fig. 4 simultaneously, this figure is the waveform schematic diagram of the A/D conversion method that provides of first embodiment of the invention.
Should illustrate that the integration of the following stated is to realize on the integrating circuit of electric capacity or other integral element composition.
Step S301, beginning.
Step S302 carries out the timing integration of negative voltage direction to zero-point voltage V0, and wherein timing is set time Td.This timing Td begins to calculate when the integral voltage zero passage.Arrive a some B as Fig. 4 mid point A.
One of difference of this method and prior art is that this method has been considered in the physical circuit owing to there is the asymmetric zero-point voltage that waits a variety of causes to cause of circuit parameter.In the method, zero-point voltage is carried out integration,, make this factor obtain considering the influence of A/D conversion as treating the threshold value that changing voltage Vx carries out linear interpolation.This step is carried out integration to zero-point voltage V0 exactly, so that calculate its influence.Described zero-point voltage V0 is the zero migration that each circuit before the integrating circuit produces.The value of described zero-point voltage V0 belongs to the parameter of physical circuit, can obtain by demarcating physical circuit.
In the present embodiment, will be to the forward integration of negative voltage direction integral as two-way integration, corresponding, to the negative sense integration of positive voltage direction integral as two-way integration.Particularly, all two-way integration processes of carrying out in the present embodiment all are to adopt at first to the negative voltage direction integral, adopt normal voltage Vb to carry out two-way integration to the method for positive voltage direction integral then.In fact, also can adopt to the positive voltage direction integral, adopt normal voltage Vb to carry out two-way integration to the method for negative voltage direction integral then, in following each step then be to the negative voltage direction integral to the positive voltage direction integral this moment.
Step S303, the time of integration, Td arrived back (B point among Fig. 4), stopped the integration to zero-point voltage V0.
Step S304 brings into use normal voltage Vb to carry out the integration of positive voltage direction, and begins counting.Arrive a some C as Fig. 4 mid point B.
Described normal voltage Vb is a voltage signal that magnitude of voltage is stable, use this signal as metered voltage in this method, to zero-point voltage V0, reference voltage V 1 and the voltage Vx to be converted that needing in the A/D conversion to carry out relating to, all be earlier to negative voltage direction integral set time Td, re-use this normal voltage Vb forward integration, begin counting simultaneously, when reaching zero crossing, stop counting, obtain a count value.Adopt the count value of this method acquisition owing to adopt same normal voltage Vb, and be the integral process that adopts same direction, therefore have good consistency.
In the present embodiment, described normal voltage Vb is a stable negative voltage that is provided by D.C. regulated power supply.
Step S305 when the integrator output voltage zero passage (as Fig. 4 mid point C), produces triggering signal, and this triggering signal makes counter stop counting.Write down this count value T0.Simultaneously, integral process is proceeded the some time.
Adopt zero crossing as the starting point of timing or the terminal point of counting in the method, can guarantee that like this each stage of A/D transfer process has identical starting point and terminal point.In side circuit, this zero crossing can adopt comparator to obtain accurately.As shown in Figure 4, corresponding with the C point, the comparator output voltage has the step sudden change at the C point, uses this step signal to stop counting as the triggering signal control counter.Below in each step, the acquisition of crossover point signal all is to adopt corresponding step signal as triggering signal.
From step S302, in this step, be integrated to zero crossing, finished a complete double integrator process, this double integrator process is carried out three times in the present embodiment, promptly respectively zero-point voltage V0, reference voltage V 1, voltage Vx to be converted is carried out double integrator.
The purpose that integration described in this step is proceeded the some time be with integral voltage reach on the occasion of so that subsequent step can produce the datum mark that zero cross signal picks up counting as timer.
Step S306 stops the integral process to normal voltage Vb, begins reference voltage V 1 is carried out regularly integration (D point among Fig. 4) of negative voltage direction, and timing is similarly Td.The triggering signal that (E point among Fig. 4) produced when the sign that picks up counting was the integrator output voltage zero passage.
Described reference voltage V 1 is a voltage signal that magnitude of voltage is known and stable, and this signal is used as the reference signal of calculating voltage Vx to be converted.Consider the requirement of the accuracy of subsequent calculations, the value of this reference voltage V 1 is near the upper limit of voltage Vx to be converted place voltage gear, so that match with the count value of aforementioned zero-point voltage V0, obtains the effect of linear interpolation.The ideal range of this reference voltage V 1 value is in the place voltage gear upper limit ± 20% scope.
Step S307, timing time reach described set time Td (F point among Fig. 4), stop the reference voltage integration.
Step S308 brings into use normal voltage Vb to carry out the integration of positive voltage direction, and unison counter is counted (the F point is to the G point among Fig. 4).
Step S309 when the integrator output voltage zero passage (G point among Fig. 4), produces triggering signal, and this triggering signal makes counter stop counting.Write down this count value T1.Simultaneously, integral process is proceeded the some time.
Above-mentioned steps S306 is used to obtain described count value T1 to step S309's.This count value T1 will be used in the calculating of A/D conversion.
In the prior art, directly carry out the A/D conversion Calculation, but because set time Td is different with the measuring and calculating standard of time T 1 that obtains by counting or T2, it is also inaccurate to calculate the transformation result that obtains according to set time Td.
The difference of A/D conversion method provided by the invention and prior art is, this method method same with the count value that obtains voltage to be converted, obtain the count value of reference voltage V 1, because the method that adopts is identical, final A/D transformation result is also just more accurate.
Behind the zero crossing, the purpose that integral process continues the some time is identical with step S305 in this step.
Step S310 as H point among Fig. 4, begins to treat changing voltage Vx and carries out regularly integration of negative voltage direction.During the integrator output voltage zero passage (I point among Fig. 4), timing begins.
Step S311, timing time reach described set time Td (J point among Fig. 4), stop to treat changing voltage Vx integration.
Step S312 uses described normal voltage Vb to begin integrator is carried out positive voltage direction integral (the J point is to the K point among Fig. 4), and unison counter begins counting.
Step S313 when the integrator output voltage zero passage (K point among Fig. 4), produces triggering signal, and this triggering signal makes counter stop counting.Write down this count value TX.Simultaneously, integral process is proceeded the some time.
Step S314 calculates Vx according to formula, and this calculated value promptly can be used as the result of A/D conversion.
Described formula be Vx=(V1-V0) (TX-T0)/(T1-T0)+V0
Compared with prior art, this formula has been considered the influence of zero-point voltage T0, should influence elimination in formula.Do not have directly to adopt the set time Td of reference voltage V 1 integration to calculate the value of voltage Vx to be converted simultaneously in this formula, and be to use the count value T1 of the reference voltage V 1 that obtains with quadrat method with Tx to calculate voltage Vx to be converted, make the result more accurate.
The essence of this formula is to carry out linear interpolation between V0 and V1, obtains the result of the calculated value of voltage Vx to be converted as the A/D conversion.Because reference voltage V 1 is chosen near the upper limit of voltage Vx to be converted place voltage gear, and adopts the circuit of A/D conversion method of the present invention to have the good linearity, therefore calculates Vx and can obtain very high precision with linear interpolation method.
Step S315 judges whether to also have next voltage to be converted; If then return step S310 (as L point among Fig. 4 to the O point); If not, then enter step S316.
Because for the voltage to be converted of same shelves, the value of V0, V1 is the same, therefore, can no longer carry out the two-way integration to V0, V1, directly carry out follow-up A/D conversion with the T0, the T1 value that have obtained.
Step S316 finishes.
See also Fig. 5.Fig. 5 is the structured flowchart of the A/D converter of first embodiment of the invention.This A/D converter is used to realize above-mentioned A/D conversion method.
Described control computation unit 51 is the kernel control chip of this A/D converter, is used for integral process is controlled, and calculates according to count value, obtains the A/D transformation result.Comprise: send order by I/O mouth line, select zero point, reference voltage and each road voltage signal to be converted to enter integrating circuit in turn, the control integral process obtains count value by rolling counters forward, and finally calculate, obtain the result and the output of A/D conversion.
Optical coupling isolation circuit 52 is used to receive the digital signal that control computation unit 51 sends, and carries out outputing to ripple counter 53 after photoelectricity is isolated; And the level signal of comparator 59 output isolated through photoelectricity output to described control computation unit 51.This circuit is used to realize the photoelectricity isolation, strengthens the antijamming capability of this A/D converter.
Ripple counter 53 is used to receive the selection information that described control computation unit 51 sends, and represents on output pin with binary code.The selection information that described control computation unit 51 sends comprises the address signal that outputs to multichannel analog signals selection circuit 54, and the multiplication factor signal that outputs to programmable amplifying circuit 56.In addition, the triggering signal that can send of described control computation unit 51 is to these ripple counter 53 zero clearings.Because the address signal of control computation unit 51 outputs is signals of serial, the multichannel analog signals of then chatting selects the address end of circuit 54 need receive the parallel binary address signal, therefore, need carry out address mapping by this ripple counter 53.
It is the multichannel analog switch that described multichannel analog signals is selected circuit 54, has a plurality of inputs, and each input is connected with one road signal of telecommunication; This multichannel analog signals selects circuit also to have the address end, is used to receive the address signal of described ripple counter output.This circuit selects corresponding input end open-minded according to the address signal of described address end, makes the output signal of the input electrical signal of this input as this circuit.The signal of telecommunication of each input input of described circuit comprises voltage signals such as voltage Vx to be converted corresponding to different voltage ranges, reference voltage V 1.
Described programmable amplifying circuit 56 is used to receive the voltage signal that described multichannel analog signals is selected circuit 54 outputs, and receive the multiplication factor signal of described ripple counter output, this programmable amplifying circuit 56 carries out the amplification of corresponding multiple according to the numerical value of described multiplication factor signal to the described voltage signal that receives, and will be through the output of the voltage signal after amplifying.
Described voltage reference circuit 55 is used to produce voltage reference signal V1.Described voltage reference signal V1 produces the voltage reference signal V1 near this grade input voltage signal upper limit according to each shelves of voltage Vx to be converted.Described voltage reference signal V1 outputs to the input that described multichannel analog signals is selected circuit 54.
Described filter circuit 57 is used to receive the voltage signal of described programmable amplifying circuit 56 outputs, and the interference signal in the voltage signal is filtered back output.
Described integrating circuit 58 receives the voltage signal of described filter circuit output, and the control command of control computation unit 51, according to described control command described voltage signal is carried out integration, the integrated signal output of acquisition.
Described comparator 59 is used to receive described integrated signal, and described integrated signal and zero-point voltage compared, produce the high-low level signal as described zero cross signal, this signal outputs to control computation unit 51 by described photoelectric isolating circuit 52, by interrupt mode, the start-stop of control counter work.
Described direct current regulation circuit 510 is used to ripple counter 53, multichannel analog signals to select circuit 54, voltage reference circuit 55, programmable amplifying circuit 56, filter circuit 57, integrating circuit 58 and comparator 59 that stable isolation voltage is provided, and comprises the normal voltage Vb that uses in the integral process.
Can under the program control of control computation unit 51, realize the A/D conversion method of present embodiment in this circuit.The concrete course of work is: described control computation unit 51 is selected described through amplifying and filtered zero-point voltage V0, reference voltage V 1, analog voltage signal Vx negative voltage direction to be converted timing integration respectively, then to normal voltage Vb signal to the positive voltage direction integral.The continually varying integrated signal of integrating circuit output compares through comparator 59 and zero-point voltage, and according to comparative result output high-low level signal, output to control computation unit 51 after isolating by photoelectric isolating circuit 52, thus the beginning of control timer timing and the end of rolling counters forward.At last, the count value T0 corresponding to each voltage of acquisition, T1, Tx, use formula Vx=(V1-V0) (TX-T0)/(T1-T0)+V0 calculates the value of Vx, with the result of this value as the A/D conversion.
As can be seen from Figure 4, during the sudden change of comparator output level generation high-low level, be exactly described zero crossing.The high-low level of this sudden change just can be used as triggering signal, and the control timer picks up counting, and counter stops counting.
See also Fig. 6, this figure is the first embodiment of the invention circuit theory diagrams.This circuit is a kind of circuit of realizing the A/D converter of Fig. 5.This specification is only done simple explanation to this physical circuit.
Described control computation unit 51 can adopt various microprocessors to realize, for example adopts MCS-51 series monolithic 89C2051 (U1 among Fig. 6), and the different situations when using according to reality also can be used the microprocessor of other model.
Optical coupling isolation circuit 52 is made up of low speed optocoupler U2, U3 and current-limiting resistance R1～R6.Wherein, optocoupler U2 is used to receive the address signal of single-chip microcomputer U1 output, and will output to ripple counter after its photoelectricity isolation; Optocoupler U3 is used to receive the comparative level of comparator output, outputs to single-chip microcomputer U1 after its photoelectricity is isolated.
The input of ripple counter 53 (U4 among Fig. 6) connects the output of described optocoupler U2, is used to receive the address signal of optocoupler U2 output, and its output connects the address end that multichannel analog signals is selected circuit (U5, U6 among Fig. 6).
It is the multichannel analog transmitter that multichannel analog signals is selected circuit 54 (U5 among Fig. 6), it has a plurality of inputs, connecting zero-point voltage, reference voltage and a plurality of input signal respectively, the voltage to be converted that wherein different inputs connect number may be in different voltage gears.According to the described address signal that its address end obtains, select corresponding input to be communicated with output.The address signal (isolation of process optocoupler in described control computation unit 51 outputs, and changing parallel binary message into by ripple counter) control is down, be in due course and select appropriate signals output, the integral process of present embodiment is achieved.
Voltage reference circuit 55 (U8 among Fig. 6) adopts power consumption little, and the standard of precision voltage of good stability, simultaneously, use several low temperature to float coefficient, carry out dividing potential drop, can obtain the accurate reference voltage of some grades of good stabilities with the precision resistance (R16, R17, R18 among Fig. 6) of material.This voltage reference circuit outputs to the input of U5, provides reference voltage to integrating circuit in due course by U5.
Programmable amplifying circuit 56 comprises many group 2 tunnels analogy transmitters (U6 among Fig. 6), several resistance (R8, R9, R10 among Fig. 6) and amplifiers (U7A among Fig. 6), by the passage control end A of control U6, the state of B, can constitute a programmable amplifying circuit that many grades of multiplication factors are arranged.
Filter circuit 57 is made up of amplifier U7D, resistance R 13 and capacitor C 4.
Integrating circuit 58 is made of amplifier U7B, resistance R 14 and capacitor C 5.Wherein capacitor C 5 is an integral element.
Comparator is amplifier U7C, its output output comparative level.Described comparative level is used to obtain the triggering signal that timer regularly begins and rolling counters forward finishes, and just carries out zero crossing and detects.
For reducing the space and saving cost, programmable amplifying circuit, filter circuit, integrating circuit and comparator also can shared amplifiers.
DC/DC circuit 58 is made of start-oscillation circuit, transformer and peripheral rectification, filtering and voltage stabilizing circuit.
In this circuit, MCS-51 series monolithic control computation unit has 2 Timer, so 2 above-mentioned circuit of may command carry out the A/D conversion simultaneously.
Foregoing circuit can be good at finishing the A/D translation function of present embodiment as the physical circuit of the structured flowchart of Fig. 5.Should illustrate, also can adopt other multiple different device and connected mode to realize the A/D converter that present embodiment proposes.Protection scope of the present invention is not limited to this physical circuit.
Though the embodiment of the invention only illustrates the situation of voltage signal being carried out A/D conversion,, the technical scheme that the present invention proposes also can be used for electric current etc. easily, and other need carry out the signal of A/D conversion.
The above only is a preferred implementation of the present invention; should be pointed out that for those skilled in the art, under the prerequisite that does not break away from the principle of the invention; can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.
Claims (18)
1, a kind of integration type A/D conversion method is characterized in that, comprising:
11) zero-point voltage V0 and normal voltage Vb are carried out two-way integration, obtain count value T0;
12) reference voltage V 1 and normal voltage Vb are carried out two-way integration, obtain count value T1;
13) treat changing voltage Vx and normal voltage Vb carries out two-way integration, obtain count value Tx;
14) use formula Vx=(V1-V0) (Tx-T0)/(T1-T0)+V0 calculates the value of voltage Vx to be converted, with A/D conversion output valve of this value as voltage Vx to be converted.
2, method according to claim 1 is characterized in that, described step 11) comprises:
21) null offset voltage V0 is carried out regularly integration of forward, wherein timing is set time Td, and this timing Td begins to calculate when integrating circuit output voltage zero passage;
22) Td time of integration to null offset voltage V0 arrives, and stops integration, begins to adopt normal voltage Vb to the integrator reverse integral, and unison counter begins counting;
23) when the integrator output voltage zero passage, produce triggering signal, make counter stop counting; Obtain count value T0.
3, method according to claim 1 is characterized in that, described step 12) comprises:
31) reference voltage V 1 is carried out regularly integration of forward, wherein timing is set time Td, and this timing Td begins to calculate when integrating circuit output voltage zero passage;
32) Td time of integration to reference voltage V 1 arrives, and stops integration, begins to adopt normal voltage Vb to the integrator reverse integral, and unison counter begins counting;
33) when the integrator output voltage zero passage, produce triggering signal, make counter stop counting; Obtain count value T1.
4, method according to claim 1 is characterized in that, described step 13) comprises:
41) treat changing voltage Vx and carry out regularly integration of forward, wherein timing is set time Td, and this timing Td begins to calculate when integrating circuit output voltage zero passage;
42) Td time of integration to null offset arrives, and stops integration, begins to adopt normal voltage Vb to the integrator reverse integral, and unison counter begins counting;
43) when the integrator output voltage zero passage, produce triggering signal, make counter stop counting; Obtain count value Tx.
5, method according to claim 1, it is characterized in that described forward integration is opposite with the integration direction of reverse integral, the forward integration can be to positive voltage direction or negative voltage direction integral, accordingly, reverse integral is exactly to negative voltage direction or positive voltage direction integral.
6, method according to claim 1 is characterized in that, after the described step 14), can directly return step 13) next one voltage Vx to be converted is carried out the A/D conversion, continues to use T0, the T1 that obtains in step 11), the step 12) this moment.
7, according to each described method of claim 1 to 6, it is characterized in that, according to the voltage range of described voltage to be converted with its stepping, for certain voltage to be converted, with this grade upper voltage limit ± voltage in 20% scope is as the value of reference voltage V 1.
According to each described method of claim 1 to 6, it is characterized in that 8, the value of described zero-point voltage V0, reference voltage V 1 obtains by demarcating in advance.
According to each described method of claim 1 to 6, it is characterized in that 9, described normal voltage Vb is that a galvanic current is pressed.
10, a kind of integration type A/D conversion equipment is characterized in that, comprises control computation unit, multichannel analog signals selection circuit, voltage reference circuit, integrating circuit, comparator, direct current regulation circuit;
Described control computation unit is used for the integral process of described integrator is controlled, and calculates according to the count value that integration obtains, and obtains the A/D transformation result; Described integral process comprises the two-way integration with normal voltage Vb to zero-point voltage V0, reference voltage V 1, voltage Vx to be converted etc., obtains count value T0, T1, Tx respectively; Described according to count value calculate to obtain the A/D transformation result be utilize formula Vx=(V1-V0) (Tx-T0)/(T1-T0)+V0 calculates;
Described voltage reference circuit is used to provide reference voltage V 1;
Described integrating circuit is used for realizing integral process according to the control of described control computation unit; Comprise two-way integration to zero-point voltage V0, reference voltage V 1, voltage Vx to be converted and normal voltage Vb;
Described comparator, be used to receive the output voltage of integrating circuit, and with this voltage and no-voltage comparison, when comparator output is undergone mutation, this jump signal is outputed to described control computation unit as triggering signal, and what beginning when being used for controlling two-way integration forward integrating meter and reverse integral were counted stops;
Described direct current regulation circuit is used to obtain the galvanic current pressure and offers above-mentioned each unit use, comprises providing normal voltage Vb to be used for described two-way integration.
11, device according to claim 10 is characterized in that, also comprises:
Multichannel analog signals is selected circuit, it has a plurality of inputs, be used to receive a plurality of input signals, comprise voltage Vx to be converted, reference voltage V 1, its address end is used for the receiver address signal, and select corresponding in a plurality of inputs of this address signal one be communicated to output as output signal, this output signal is as the input of described integrator.
12, device according to claim 11 is characterized in that, also comprises
Ripple counter is used for the receiver address signal, and this address signal is converted into parallel binary address signal, selects the address signal of the address end of circuit as outputing to described multichannel analog signals.
13, device according to claim 12 is characterized in that, also comprises
Optical coupling isolation circuit is used to receive the address signal that described control computation unit is exported, and carries out outputing to described ripple counter after photoelectricity is isolated; And the triggering signal that receives described comparator output, through outputing to the input of described control computation unit after the photoelectricity isolation.
14, device according to claim 10 is characterized in that, also comprises
Programmable amplifying circuit, be used to receive described reference voltage, voltage to be converted, and the multiplication factor that receives control computation unit output, according to described multiplication factor, behind described reference voltage, the corresponding multiple of voltage amplification to be converted, as input to described integrator.
15, device according to claim 14 is characterized in that, also comprises filter circuit, is used to receive the voltage signal after the described amplification of described programmable amplifying circuit output, and after the interference signal in this signal filtered, is re-used as the input of described integrator.
16, device according to claim 10 is characterized in that, described control computation unit is a microprocessor.
17, device according to claim 10 is characterized in that, described voltage reference circuit comprises a standard of precision voltage and several precision resistances; Standard of precision voltage by several precision resistance dividing potential drops after, produce several reference voltages, the value of described reference voltage is near the upper limit of stepping of voltage to be converted ± certain voltage in 20% the scope.
18, device according to claim 10 is characterized in that, described programmable amplifying circuit comprises amplifier, multiway analog switch and resistance; Multiway analog switch and resistance cooperate, and are made of the amplifier of various multiplication factor control computation unit control.
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| JPS6013614B2 (en) * | 1979-08-27 | 1985-04-08 | タケダ理研工業株式会社 | analog to digital converter |
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