Abstract:
A method and a device for detecting at least one first signal for a computer is described, having a converter device which converts the first signal to a second signal, and including a reference device to which a first reference signal is applied and which converts it to a second reference signal. Also included is a first switching element which can switch the second reference signal to the converter device, the converter device converting the second reference signal to a third reference signal. The method and device described herein also include a matching arrangement, which also receives the second reference signal and matches the second reference signal to a fourth reference signal, and at least a second switching element which can switch the fourth reference signal to the converter device, which then converts it to a fifth reference signal. Also included is a comparator element with the help of which a correcting quantity is formed from the third and fifth reference signals, the first signal being detected as a function of the correcting quantity.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and a device for detecting at least one signal for a computer, the signal being converted by a converter device. 
     BACKGROUND INFORMATION 
     Many different converter devices are known from the related art, in particular analog-to-digital converters and digital-to-analog converters. Such converter devices or signal converters are used in the related art for converting physical quantities to a voltage, for example. 
     Corresponding converter modules are known from the technical book “PC-gesteuerte Meβtechnik” (PC-Controlled Measurement Technology) by Klaus Dembowski from Marktund Technik-Verlag in 1993 (ISBN 3-87791-516-7), pages 169 through 206, where it is pointed out that in many cases, a converter module requires an additional periphery of analog and digital components to make it possible to work accordingly. For example, a multiplexer is required for detecting signals in multiple channels. 
     German Published Patent Application No. 37 00 987 describes a device for detecting an electric voltage signal for processing in a microcomputer in which at least one analog-to-digital converter is provided with a word of n bits, and in which it is possible to display the voltage to be measured by an additional digital-to-analog converter and an external circuit with the same accuracy of n bits, but with a higher monotonic resolution over the entire measurement range. The complete monotony of the more highly resolved measurement result is then achieved by software routines in the microcomputer on the basis of simple limit value comparisons. 
     The accuracy of such converter devices depends first on the signal level, in particular the voltage, for which the converter device or the computer containing it is intended, and secondly, it depends on the resolution of the converter device. 
     In general, it is known that signal matching can be performed with the help of a matching arrangement, e.g., a voltage divider. 
     Thus, if the level of the signal to be detected is different from the intended signal level at the input of the converter device, signal matching could be performed by a matching arrangement, but inaccuracies in the matching arrangement would be reflected directly in the conversion result. Thus, if the signal level of the signal to be measured or converted is different from, in particular higher than, the maximum signal level intended for the converter device, in particular the A/D converter, then it could be converted by a matching arrangement, in particular a voltage divider, only with a lower accuracy. Influencing quantities here include, for example, the temperature, inaccuracies in the matching arrangement, in particular in the resistors of a voltage divider, and aging phenomena, in particular in the resistors of the voltage divider. This loss of accuracy is manifested in a very interfering manner in particular since the inaccuracies in the converter device itself, e.g., due to nonlinearities or offset, usually turn out to be lower by a power of 10 than the inaccuracies in the matching arrangement, in particular the voltage divider. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is thus to compensate for the loss of accuracy when using a matching arrangement which matches the input signals or the input signal level to the intended signals of the converter device or the computer containing the converter device and thus to compensate, i.e. to achieve an increase in accuracy. An improvement in the properties of a converter device, in particular an analog-to-digital converter, is thus to be achieved in this regard. In the concrete case of the analog-to-digital converter, this means that a 5V input signal, for example, can be applied via a voltage divider as a matching arrangement to a 3V analog-to-digital converter or to the corresponding input of a computer and converted without any loss of accuracy. 
     This object is achieved by a method and a device for detecting at least one first signal for a computer, the first signal being converted to a second signal by a converter device. In an advantageous manner, a first reference signal is applied to a reference device which converts it to a second reference signal, the second reference signal being switched to a converter device which converts it to a third reference signal, the second reference signal also being switched to a matching arrangement which matches the second reference signal to a fourth reference signal, the fourth reference signal also being switched to the converter device which converts it to a fifth reference signal, a correcting quantity being determined from a comparison of the third reference signal and the fifth reference signal in the computer, and the first signal being detected as a function of this correcting quantity. 
     In an expedient embodiment, the first signal is detected as a function of the correcting quantity in such a way that the first signal is converted to the second signal as a function of the correcting quantity, and the first signal is detected by analyzing the second signal, so that the correcting quantity determined has an influence on the conversion itself. 
     A next expedient embodiment is characterized in that the first signal is detected as a function of the correcting quantity in such a way that the first signal is converted to the second signal, and the second signal is matched to a third signal as a function of the correcting quantity, the first signal then being detected by analyzing the third signal, so the second signal converted from the first signal is linked to or influenced by the correcting quantity. 
     In this way, a computer having a first voltage, e.g., 3V, can convert signals having a different voltage, in particular a higher voltage, e.g., 5V, by using a normal matching arrangement, such as an internal or external voltage divider with a greatly improved accuracy, in particular in the case of an input signal having a voltage higher than the voltage at which the computer operates. 
     This makes it possible to eliminate process costs in the computer for a special converter device, usually an additional device, in particular an analog-to-digital converter, having a voltage different from the computer voltage. On the other hand, only low additional costs are incurred by integrating or attaching the device according to the present invention or the elements and connections thereof which are not yet included. 
     The correcting quantity can be determined repeatedly to advantage at preselectable intervals, which may be the same or different, and/or as a function of times of certain events, e.g., clocked signal acquisition. This method can thus also be used repeatedly in the operation of the computer in an advantageous manner to compensate for temperature-dependent changes or leakage currents, for example. This also makes it possible to eliminate changes in the matching arrangement due to aging, so a loss of accuracy in this regard can at least be compensated, and in general a definite increase in accuracy can even be achieved, because even internal inaccuracies, including those not due exclusively to the matching arrangement, can be compensated according to the present invention. 
     In addition, it is also advantageous that the first reference signal can be preselected to be variable so that the third reference signal, which is converted by the converter device, and the first reference signal correspond within preselectable tolerances, in particular they are identical at a desired tolerance of 0. In the case of a digital-to-analog converter as a reference device, this means in concrete terms that the voltage can be applied with a very high accuracy, because voltage is read back over the same circuit or an identically dimensioned circuit, and thus the voltage, which has undergone a digital-to-analog conversion, can be corrected. This control mechanism makes it possible to use matching arrangements which have a lower accuracy and are therefore less expensive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a schematic diagram of an arrangement according to the present invention in or with a computer. 
     FIG. 2 shows a special embodiment having an analog-to-digital converter, a digital-to-analog converter, transistors as switching elements and a voltage divider. 
     FIG. 3 shows a flow chart of the method according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a computer  100  which is used to control operating sequences in a motor vehicle, for example, having a computer unit or a processor unit  106  and a memory  105  assigned to it. For reasons of simplicity, the input/output signal paths are represented symbolically with double arrows  110  and  111 .  101  indicates a matching arrangement for matching an applied signal S 1  and the properties of the signals processed in computer  100 . A reference signal Rs 1  is applied to a reference device  103  which makes it available as a converted signal (Rs 2 ) at point I. Reference signal Rs 1  can be preselected and can in particular be generated automatically, e.g., by processor unit  106 . A first switching element  107  switches the converted first reference signal, i.e., reference signal Rs 2 , through from point I to point III. The signal is switched through by applying a control signal As 107 . 
     Then the signal is applied to converter device  102  at point III and can be converted by it. This converted signal Rs 3  can then be stored in a memory device, e.g.,  105 , or another memory device provided specifically for this purpose. At the same time, signal Rs 2 , which is converted reference signal Rs 1 , is applied to matching arrangement  101  at point V, is matched there and appears as reference signal Rs 4  at point IV. Another switching element  108  may optionally be provided to actively switch reference signal Rs 2  through from point I to point V, which can be accomplished by applying a control signal As 108 . 
     Reference signal Rs 4  is then switched through from point IV to point III using switching element  109 , which can be accomplished by applying a control signal As 109 . This reference signal Rs 4 , which is sent over matching circuit  101 , is then also converted (Rs 5 ) in converter device  102  and stored in a memory, in particular memory  105  or a memory provided specifically for this purpose, or it may also be compared immediately with previous reference signal Rs 3 . 
     This comparison can be performed either by a processor unit or computer unit  106  or optionally by a comparator device  104  which is provided specifically for this purpose. There is preferably no additional input signal S 1  during referencing, i.e., switching through and processing of the reference signals. 
     Thus, the principle according to the present invention is to supply an accurate signal at point I, and to measure or detect this signal by converter device  102 , the accurate signal being passed through matching arrangement  101  at point I. A comparison of the two converted signals (Rs 3  and Rs 5 ) then makes it possible to determine a correction factor which compensates for temperature effects, aging phenomena and other influencing parameters, based on the accuracy of the conversion. 
     The matching arrangement and the leads to it can be secured and connected outside of computer  100  or they may be integrated into it, which is indicated as optional by the diagram of computer  100   a.    
     Switching elements that can be used include transistors, controlled switches and the like. Likewise, a comparator arrangement, in particular with comparison of threshold values or a voltage divider circuit and the like may also be used as the matching arrangement. The reference device may be a converter, e.g., a frequency-to-voltage converter or a digital-to-analog (D/A) converter, a signal generator or the like. Various embodiments are also conceivable for the converter device, such as an A/D converter, a voltage-to-frequency converter and the like. 
     FIG. 2 shows a concrete embodiment of the device according to the present invention, using an analog-to-digital converter  102   e  as the converter device and a digital-to-analog converter  103   e  as the reference device. 
     As already mentioned in the introduction, an analog/digital input multiplexer, indicated here by transistors  202 ,  109   e  and  204 , is used in computer  100   ae  when multiple signal channels are used. To minimize the error in the transistors, they may be selected to be the same, in which case  201 ,  108   e  and  205  on the one hand and  202 ,  109   e  and  204  on the other hand may each be designed differently as a group. 
     The numbering in FIG. 2 is selected so that elements which are specified more precisely for this specific embodiment in comparison with FIG. 1 are indicated by an additional “e” for “example,” i.e., converter device  102  and reference device  103  from FIG. 1 are represented by an A/D converter  102   e  and a D/A converter  103   e  in this specific embodiment. 
     According to the number of channels, an input pin P is needed for each channel, so that a transistor arrangement consisting of transistors  201 ,  108   e  and  205  is shown accordingly. 
     The matching arrangement, shown here as voltage divider  101   e  composed of resistors  206  and  207 , is integrated into computer  100   ae  in the embodiment in FIG. 2, but it can also be located outside the computer, as illustrated in FIG. 1, and only connected to it according to the present invention. 
     Other transistors in accordance with the use of multiple channels are indicated as  204  and  205 . Transistors  201  and  202  are preferably used as switching element  107   e  and are controlled accordingly for switching through from point I to point III. Switching element  109  corresponds to transistor  109   e  and switching element  108  corresponds to transistor  108   e . The control signals illustrated in FIG. 1 switch over the control pins of the transistors. 
     Two resistors  206  and  207  of matching arrangement  101   e  have an accuracy of 1%, for example. This is usually at least one power of ten greater than the accuracy of a conventional analog-to-digital converter, which is in the order of 0.1%. This loss of accuracy can be compensated according to the present invention. Here in FIG. 2, signal S 1  corresponds to a voltage Us 1  which is applied upstream from resistor  203  and is supplied to the computer through the pin at point V. This voltage Us 1  or signal S 1  is then converted to signal S 2  by the converter device, in particular A/D converter  102   e , with previous referencing of the device according to the present invention, and is thus detected. When using multiple channels, the analog/digital input multiplexer composed of transistors  202 ,  109   e  and  204  is controlled by multiplexer software. This multiplexer software can also be used to control transistors  201 ,  108   e  and  205  in accordance with the number of channels. 
     The concrete control sequence and operating sequence are explained again with reference to a flow chart in FIG.  3 . 
     The method starts in block  300 . In block  301 , a reference signal Rs 1  is supplied to reference device  103  which converts it to a reference signal Rs 2  at point I. Based on the concrete embodiment in FIG. 2, this means that from a preselectable digital reference signal, in particular a signal selected by processor unit  106 , an analog voltage is set as reference signal Rs 2  by digital-to-analog converter  103   e  at point I. 
     This reference signal Rs 2  is subsequently switched through to point III in block  302 , which is accomplished by switching element  107  and control signal As 107 . Based on the concrete embodiment, this means that transistors  201  and  202  are switched through or become conducting by a control signal at the control pin, i.e., switching element  107   e  is switched through, so the set voltage, as reference signal Rs 2  at point III, is applied to the converter device, i.e., specifically analog-to-digital converter  102   e  here. 
     Then in block  303 , reference signal Rs 2  applied at point III is converted to a reference signal Rs 3  by converter device  102 . In particular, this reference signal Rs 1  is stored in a memory, e.g., memory  105 , which is provided for this purpose. Based on FIG. 2, this means again that the set voltage, as reference signal Rs 2  at point III, is converted back by analog-to-digital converter  102   e  to a digital quantity as reference signal Rs 3  and is stored in this form. This signal holding or signal storage of Rs 3  is continued until Rs 5  is available for comparison; this may also be accomplished by other volatile storage media. 
     Then in block  304 , reference signal Rs 2  is sent to matching arrangement  101 . This can be accomplished in a controlled manner, for example, by using switching element  108  and control signal As 108 . Also based on FIG. 2, this means that transistor  108   e  switches through the set voltage as reference signal Rs 2  at point I to point V upstream from matching arrangement  101   e , here a voltage divider having resistors  206  and  207 . 
     In block  305  which follows, reference signal Rs 2  is then converted or matched to reference signal Rs 4  at point IV by the matching device or the matching arrangement and is also switched through by switching element  109  and control signal As 109  at point III, applied reference signal Rs 4  then being converted to a reference signal Rs 5  by converter device  102 . 
     Based on FIG. 2, this means in turn that reference signal Rs 2 , which is switched through to point V, is converted to reference signal Rs 4  at point IV by voltage divider  101   e . Then transistor  109   e , determined by an actuation at its control pin, switches this signal Rs 4 , i.e., the voltage applied there, through to point III, where it is converted to a digital signal Rs 5  by analog-to-digital converter  102   e.    
     Then in block  306 , there is a comparison of the two reference signals Rs 3  and Rs 5  which are generated. This can be accomplished by forming the difference, by threshold comparison, by forming a ratio, etc. In a special embodiment, the difference between reference signals Rs 3  and Rs 5  is formed here. This comparison results in a correcting quantity which is used in the remaining process and reflects the prevailing situation, based on the accuracy or inaccuracy with respect to the effect of temperature, inaccuracies in the matching arrangement, etc. 
     Then in block  307 , the correcting quantity thus determined is stored. This can then be used as a correction factor, a correction addend, etc., depending on the desired compensation or determination of the correcting quantity. 
     Inquiry  308  determines whether the method is to be continued further or whether it is terminated. This means whether referencing is to be continued as described or whether or not a signal S 1  or voltage Us 1  applied at the input is converted. Termination at this point can be carried out, for example, by a preselectable termination condition, so that the method then branches off to the end of the method in block  310 . 
     If the method is continued, it goes to inquiry  309 , where an inquiry is made as to whether referencing is to take place as described above, or whether with the help of the correcting quantity thus determined, an applied signal S 1  or Us 1  is to be converted. If this is the case, it leads to block  310 ; otherwise, referencing is run through again after block  301 . The conditions may be preselected (even in block  308 ) or used as a time condition (clock cycle) or as an event-controlled basis. 
     In block  311 , applied voltage Us 1  or applied signal S 1  is matched to pin P by the matching arrangement and switched through to point III, either by switching element  109  with control signal As 109  or the voltage with transistor  109   e.    
     In block  312  which follows, the signal or voltage applied at point III is converted by converter device  102 , in particular analog-to-digital converter  102   e , to signal S 2 , in particular a digital signal. 
     The conversion can then take place in such a way that the converter device converts the signal applied at point III to signal S 2 , taking into account the correcting quantity, so that the inaccuracies are already compensated in the conversion or the signal conversion. Secondly, a conversion of the signal at point III can take place easily, and then the correcting quantity is linked as a factor or as an addend to resulting signal S 2  to yield a signal S 3 , which then represents signal S 1 , so that signal S 1  is detected, and which is then present with compensated inaccuracies. This can be accomplished, for example, by processing unit  106  or optionally also by a special comparator device  104  with regard to the referencing. 
     The method shown here or the individual steps can also be represented in the software, e.g., as a computer program having a program code arrangement. Then the individual steps are carried out with sequence control or time control based on a control program or a computer program, which can then be stored as a computer program product having a program code arrangement on any desired computer-readable data medium (CD-ROM, EEPROM, flash memory, RAM, disk, etc.). 
     In the case of a special embodiment, a 3V or 3.3V A/D converter receives a 5V input signal with the help of a voltage divider. Based on this embodiment, computers lower than 3.3V or the corresponding A/D converters can in principle also be operated by this method. In other words, the same resolution can be achieved or the accuracy can be maintained or improved even with a lower voltage. Thus, the advantages mentioned above and the other advantages deriving from the description can also be achieved.