DE102013108510B4 - Charge flux-frequency converter with different charge flow direction - Google Patents

Abstract

A converter device (2, 34) for converting a charge flow (4) into a frequency signal (23) comprising at least one integrator (5, 5a, 5b) and at least one comparator (16, 16a, 16b, 39a, 39b, 39c) at least one integrator (5, 5a, 5b) and at least one comparator (16, 16a, 16b, 39a, 39b, 39c) are connected in series and the comparator (16, 16a, 16b, 39a, 39b, 39c) when an integrated charge flow is exceeded relative to a threshold voltage (19) and / or a comparison voltage (36, 37, 38) emits a signal (23), characterized by at least one charge flow direction selection device, with which the converter device (2, 34) selectively to a positive or a negative charge flow (4) can be set.

Description

The invention relates to a converter device for converting a charge flow into a frequency signal which has at least one integrator and at least one comparator, wherein at least one integrator and at least one comparator are connected in series and the comparator outputs a signal relative to a threshold value when an integrated charge flow is exceeded.

Charge flux-frequency converters are used when it is necessary to measure an electrical charge flow of typically low intensity. Such charge fluxes occur, for example, in particle accelerators (for example electron particle accelerator, proton particle accelerator or ion particle accelerator, in particular heavy ion particle accelerator) or in particle detectors (for dosimetry purposes, for measuring arrangements and the like). The currents to be measured in this case are typically in the range between a few 10 fA up to several 100 uA. It is readily apparent that at such low current levels, "classical measurement techniques" which operate, for example, with a voltage drop across a resistor or with the current-induced magnetic field (eg, spin-coil instruments) do not provide sufficient accuracies or even fail completely.

In some areas, however, precise measurement of (particle) current (in particular electron current or ion current with comparatively low current intensity) is required with high accuracy. This applies in particular to some research applications, but especially to the field of medical technology. Since particle accelerators are now used very successfully in medical technology (both electron accelerators and ion accelerators), there is a need for high-precision measuring devices and measuring methods which nevertheless should be as cost-effective as possible.

One way to be able to measure such small electrical currents with high accuracy is the use of charge flow frequency converters. In these, the charge flow in an integrator is integrated over a certain period of time. Once a certain charge has accumulated in the integrator, an output signal is output and the integrator is simultaneously reset to zero ("cleared") to be available for a new measurement cycle. Since the frequency of the output signals corresponds to the incoming charge flow, the frequency of the output signal can be used as a measure of the charge flow.

Such charge flow frequency converters have been known for some time. A problem with these is that during the "reset phase" of the integrator no charge flow can be measured. This creates a certain inaccuracy of measurement. In some fields of application (such as in medical technology or in some research accelerators), the associated measurement inaccuracy is unacceptable; in other fields of application, it is at least undesirable. Therefore, in the German Offenlegungsschrift DE 198 41 308 A1 proposed to provide two mutually parallel measuring branches, each with an integrator. The two integrators are interconnected in terms of circuitry such that the incoming charge flow is first directed into a first branch. As soon as the first integrator branch has reached its threshold value, it outputs a signal, switches the signal to be measured to the input of the other integrator branch and then resets itself. Meanwhile, the second integrator branch fills, and when the threshold is reached, it outputs a signal, the circuit returns to the first integrator branch, and the second integrator branch is reset. Since during the "dead time" of the integrator branch, in which this is reset, the other integrator branch takes over the measurement of the charge flow to be measured, it does not lead to the unwanted dead time losses described and thus not to measurement inaccuracies.

A major problem with known charge-flux-frequency converters is that they are constructed exclusively either for negative charge fluxes (given for example in electron accelerators) or for positive charge fluxes (given for example in ion accelerators). Accordingly, different charge flux-frequency converters must be used in a polarity change of the charge flow to be measured. This does not restrict the universal usability of such charge flux-frequency converters significantly. In particular, this increases the logistical effort, both in production and in sales and storage.

From the EP 0 341 691 A1 For example, a detection voltage output circuit of a charge generation type sensor device is known. This converts a voltage due to a change in charges generated on the sensor device from the outside, and outputs the voltage thus obtained.

From the US 4,124,821 A For example, an analog frequency converter is known for forming an output frequency proportional to a measurement current or a measurement voltage. This works according to the charge amount compensation method with an integrator, a downstream of this threshold switch and a compensation charge generator each of which supplies a constant compensation charge to a capacitor of the integrator.

From the US 3,921,012 A is a broadband current-frequency converter for an analog / digital conversion known. This comprises an amplifier and a charge generating means which is arranged at the output of the amplifier and generates output pulses, wherein the output pulses have a frequency which is directly related to the signal current which is applied to the input of the amplifier means.

From the US 3,959,653 A For example, a charge digitizer is known having a charge integrator connected to an ionization chamber which outputs an output current that is proportional to the ionizing radiation. The charge integrator is connected to a comparator which transitions from a high state to a low state when the output of the integrator rises above a threshold. The digitizer also has a bistable multivibrator that generates a train of pulses that are fed back into the integrator through an analog switch. As a result, charge is removed from the charge integrator so that it falls below the threshold again. The output signal is coupled out between the multivibrator and the analogue switch and counted.

Accordingly, there has long been a desire for charge-flux-frequency converters that are as universally applicable as possible and, in particular, can be used both in conjunction with negative charge flows and with positive charge flows. So far, however, it lacked this circuit concepts that provide such functionality with the least possible hardware cost.

The object of the invention is therefore to propose a converter device for converting a charge flow into a frequency signal, which is improved compared to converter devices for converting a charge flow into a frequency signal, as are known in the prior art.

The invention solves this problem.

It is proposed a converter device for converting a charge flow into a frequency signal which has at least one integrator and at least one comparator and in which at least one integrator and at least one comparator are connected in series and the comparator is a signal when an integrated charge flow is exceeded relative to a threshold value to provide with a charge flow direction selection device with which the converter device can be set to either a positive or a negative charge flow. The currents to be measured are typically in the range from a few 10 fA to several 100 μA, in particular between 100 fA and 130 μA, for example in the case of particle accelerators or particle detectors. In this case, the converter device can be constructed in any desired manner from discrete components or else as an integrated circuit (in particular in an ASIC (for "application-specific integrated circuit")). It is of course also possible that a "partial integration" takes place in an integrated circuit, so that although some discrete components are still present, but a preferably larger proportion of components is integrated into the integrated circuit. In principle, the greatest possible integration into an integrated circuit is advantageous. On the one hand this can be cost savings, the required space can be reduced, it is generally possible that the converter device must be supplied with less electrical energy and moreover charge losses (especially of current to be measured) can be largely avoided. The integrator is usually designed such that (parts of) the charge flow are conducted into a capacitance. It is preferred that the size of the capacitance can be changed in order to be able to adapt the converter device to different currents. The "switching" between different capacities can be done in hardware (for example by external capacitors on or off), but also a changed wiring (using different input pins) or a suitable programming of an integrated circuit. Typical values for the capacitances lie in the range between 2.5 pF and 25 pF, so that, with typical charge flows in the range between 100 fA and 130 μA, a charge resolution which is advantageous for further processing (amount of charge required to output a pulse) as well as pulse frequency. However, other capacities are also conceivable, in particular 1 pF, 2 pF, 3 pF, 4 pF, 5 pF, 6 pF, 7 pF, 8 pF, 9 pF or 10 pF as lower limit and / or 10 pF, 20 pF, 30 pF, 40 pF, 50 pF, 60 pF, 70 pF, 80 pF, 90 pF or 100 pF as the upper limit. It is particularly advantageous in the case of the abovementioned capacities that they can be provided comparatively easily in an integrated component, which can bring about corresponding advantages. The proposed capacitance values are therefore particularly advantageous for integrated circuits because an advantageous "compromise" can be achieved here. On the one hand, the capacities are so great that the parasitic capacitances in the production can generally be essentially neglected; On the other hand, the capacities are so small that they can be produced economically on a semiconductor chip. It is advantageous if (in the case of a "reversibility" of the capacity) a "capacity dynamics" with a ratio factor of 1: 1, 1: 2, 1: 3, 1: 4, 1: 5, 1: 6, 1: 7 , 1: 8, 1: 9, 1:10, 1:15, 1:20, 1:25, 1: 30, 1:40, 1:50 or 1: 100 are provided (the values given are both can represent a lower as well as an upper interval limit). Of particular advantage is a "decadal subdivision" (ie in particular 1: 10 or 1: 100), because this is particularly comprehensible for the human imagination. In this case, it is in particular possible to realize an advantageous compromise of simple construction on the one hand and the greatest possible adaptability to different current strengths on the other hand. Typically, the integrator outputs an output signal that corresponds to the already accumulated charge. Thus, for a constant current, for example, a voltage output increases linearly with time. As soon as the output signal exceeds a certain value (threshold value), an action is taken (preferably using the comparator, which in particular makes a comparison between the output value of the integrator and the current threshold value). The action can be different in nature. In particular, it is possible for a pulse-like output signal, for example, to be output (frequency signal as output signal), a reset of the integrator ("charge erasure"), or else an adjustment of the threshold value. In particular, with an "adjustment of the threshold value" it is possible to be able to generate a comparatively high-frequency signal and, in addition, to be able to increase the measurement accuracy, in particular by avoiding dead times. It is also possible that the threshold is increased and only after a multiple increase of the threshold, an output signal occurs (whereby it is possible that with each adjustment of the threshold value or, for example, only with a provision of the threshold, an output signal is output). Incidentally, the threshold voltage can be provided in an arbitrary manner by an external signal, but also by an internally generated signal. The charge flow direction selection device can also be realized in different ways. On the one hand, a fully automatic conversion is to be considered. However, it is also possible that the converter device, depending on the existing current polarity, must be supplied with the current via a different input terminal (optionally a switching device, which may be both external and internal, can be provided). In particular, it is also possible that a conversion to different current directions takes place by programming the converter device and an optionally required switching by internally provided switching elements is provided.

It is preferred if the converter device is designed in such a way that it has at least two integrators or integrator branches connected in parallel to one another, which are charged alternately with the charge flow. With such a structure, it is possible, in particular, that the dead time which occurs during a reset of an integrator (and inherently unavoidable in principle, occurs, for example, by discharging the capacitances) does not lead to a deterioration in the measuring accuracy due to "loss of the measured value Carriers "comes. Because according to the proposed development, the charge flow during this dead time can be measured by the other integrator. As a result, the measurement accuracy can be significantly increased in a simple manner. Incidentally, it is entirely possible that, in particular over short time intervals, both integrators are also "charged" with a charge flow (in the case of two integrators, each integrator is essentially charged with half the charge flow) in order to make switchover phases particularly advantageous and thereby, for example, to further increase the measurement accuracy. But it is also possible that only a single integrator or a single integrator branch is used. Such a construction of the converter device is usually particularly simple and therefore particularly favorable. The loss of "measured charge flow" can be at least partially compensated by the fact that, for example, the dead time is "numerically balanced" by a correction factor. However, this is not a true measurement, but merely a kind of "simulation", in particular the charge carrier peaks or short-term dropouts are not detected.

A further possible embodiment of the converter device results if, in the case of the converter device, the charge flow direction selection device preferably supplies the integrator and / or the comparator mutually with in each case one of two charge flux reference voltages. The charge flow reference voltages may differ in terms of their height and / or their sign. In general, it makes sense that the charge flow reference voltages differ essentially only in terms of their sign. This can be for both positive as well as negative charge flows an approximately equal measurement behavior of the converter device can be realized. Incidentally, it is basically possible for the charge flow reference voltages to be provided by "external components". However, it is also possible for the charge flow reference voltages to be provided by the converter device itself, in particular also by a part of the converter device which is designed in the form of an integrated circuit.

It is particularly preferred if, in the case of the converter device, the charge flow direction selection device has at least one changeover switch device. As a result, the same charge-flux reference voltages can be used both for the integrator and for the comparator. These are supplied to the integrator or the comparator respectively by means of the change-over switch device. As a result, the number of reference voltages to be provided can advantageously be reduced, which helps to reduce the construction costs. The changeover switch device can be switched either by means of mechanical contacts, but also by means of electronic switches. A "changeover switch device" is to be understood in particular as a device in which a first voltage is applied to the integrator and a second voltage to the comparator in a first switching state, while in a second switching state a second voltage is applied to the integrator and a first voltage is applied the comparator is created.

Furthermore, it is proposed to design the converter device in such a way that the comparator is followed by a preferably conditional signal inversion device, which preferably has an inverting function as a function of the position of the charge flow direction selection device. The signal inversion device can be designed in particular as an exclusive-OR logic device. It has been found that in a conventional construction of the converter device, in particular when an output signal of an integrator is supplied to a comparator and compared therewith with a charge flow reference voltage and / or a threshold voltage, the signal output logic of the converter device is (initially) different, depending on whether a positive or a negative charge flow is measured. If, depending on the polarity of the measured charge flow, a signal inversion device is switched on or off, the "output logic" of the converter device can remain the same despite the different polarity of the charge flow. This is particularly conducive to further processing of the signal output by the converter device. In particular, the converter device can then be used particularly simply as a "drop in" solution.

It is furthermore preferred if, in the case of the converter device, the integrator has an operational amplifier and, in particular, the charge flow input signal is connected to the inverting input of the operational amplifier and / or the charge flow reference voltage is connected to the non-inverting input of the operational amplifier. It makes sense if the integration capacitance is arranged in the negative feedback path between the output and the inverting input of the operational amplifier. Operational amplifiers are differential amplifiers which have a very high gain and a high input resistance. The proposed circuit variant has proven particularly useful since the operational amplifier can be used to decouple the input from the integration signal. The input can be kept constant at the voltage set via the non-inverting input. Accordingly, it is useful to connect the non-inverting input to the charge-flux reference voltage. In particular, operational amplifiers can be designed to be particularly high-impedance, so that the leakage currents occurring are particularly low. Such behavior is especially advantageous for the presently proposed use (measurement of small charge flows). In particular, the proposed circuitry (especially when implemented in combination) has proven to be advantageous for generating the desired frequency output signal. It is further preferred if operational amplifiers with MOS-FET inputs are used as operational amplifiers, since these are particularly high-impedance and therefore particularly low-loss.

Furthermore, it is proposed to implement the converter device such that the comparator has a comparator component and in particular the output signal of the integrator is connected to the non-inverting input of the comparator component and / or a threshold voltage is connected to the inverting input of the comparator component. In particular, the threshold voltage may be a threshold voltage generated by a digital-to-analog converter or another reference voltage. The advantages of operational amplifiers already described in connection with the integrator also apply analogously to the comparator (s) or the comparator component (s). Accordingly, suitable comparator components are advantageous here. The proposed circuit (in particular in combination) is particularly suitable for realizing the functionality of the converter device in a simple and effective manner.

It is also proposed that in the converter device, the output signal of the comparator and / or the output signal of the signal inversion device is supplied to a pulse shaping device. In this way, each time "one unit" of the charge flow has been delivered, a defined pulse can be delivered. The pulse shaping device may be used to return a signal to the transducer device (for example, to effect a switchover of the "active integrator branch") or to cause a reset of an integrator. It is also possible that such a generated pulse signal serves to increase a threshold voltage at the comparator, so that prior to a reset of the integrator and / or a change of the integrator branch of the integrator concerned "count up" and in this way switching operations (and possibly also dead times ) can be reduced, even if comparatively large flows of charge are to be measured by the converter device.

According to a preferred embodiment, it is proposed to provide the converter device with a digital counter device and / or with a digital-to-analog converter which can supply different comparison voltages to the comparator, in particular as a function of an output value of the comparator, preferably as a function of a count value of the counter. In this way, the number of reset operations in the integrators of the converter device can be reduced. This can in particular help to reduce dead times and measurement errors in the components of the converter device. Depending on the embodiment, a high frequency can nevertheless be output at comparatively low charge flows, so that a comparatively high sensitivity of the converter device can be realized. In a construction following this proposal, the threshold voltage supplied to the comparator usually follows a kind of stepped sawtooth curve. In each step up a frequency pulse can be output (not only to the digital-to-analog converter or to the digital counter, but in particular to an output terminal of the converter device). A digital counter can be understood to mean both positive and negative counters. It is preferably a counting device which can be used both as an up-counter device and as a down-counter device depending on an input signal or a programming. It is possible that the counter has the possibility for a reset (applying a reset signal). Additionally or alternatively, the counter can also be provided with an "overflow", such that the counter automatically jumps back after passing through a certain number of counting steps (for example after 4 steps, after 8 steps, after 16 steps, after 32 steps or the like ) "jump back to start" again.

Furthermore, it is proposed that a digital-to-analogue-to-bandwidth signal input means be provided in the converter device. Here, for example, programming can be used to specify after how many increasing steps the comparator-supplied threshold voltage returns to zero. For example, it may be specified that after four, eight or sixteen steps of incrementing, the threshold voltage returns to zero again (optionally switching to the other integrator branch if present). By means of such (previous) programming, the converter device can advantageously be set to different expected or to be measured input charge fluxes, so that the converter device can be used in a particularly universal manner.

It is further proposed to provide in the converter device a reset signal output means which resets an integrator and preferably activates another integrator. With such a reset signal, the converter device can be decided and controlled "internally controlled". In particular, the reset signal output means may be supplied to input switches which supply the input charge flow to different integrator branches. In addition, the "reset" of an integrator can be effected by the reset signal output means and optionally also a digital-to-analog converter (which in particular provides a threshold signal for a comparator) or a digital counter can be reset to "zero".

Furthermore, it is proposed that at least one self-adjusting charge flow direction selection device be provided in the converter device. In such a particularly preferred construction of the converter device, not even pre-programming of the converter device is usually required to determine whether a positive or negative charge flow is to be measured. With such a construction, the converter device is particularly fail-safe and particularly universal to use (where it is of course possible to vorzuprogrammieren the converter device with a kind of "expected value"). In particular, in the case of multiple branches, a branch may communicate such an "expectation value" to a branch following the "integrate order".

Furthermore, it is proposed to provide the converter device with at least one frequency-exceeded signal output device. Such a frequency-exceeding signal output device can indicate, in particular, if the incoming charge flow is so high that the converter device no longer has enough time to reset itself and in this way the measurement error increases intolerably (this also applies in particular to the case) of two or more integrator branches, if the integrator branch needs to be changed more quickly than the resetting time of an integrator). The output signal of the frequency-exceeded signal output device can then be used as a kind of error signal, so that, for example, an emergency shutdown of the system, for which the converter device is used, can take place, since a safe operation of the same can no longer be guaranteed.

Furthermore, it is proposed to design the converter device in such a way that the frequency-overflow signal output device has at least one error indication comparator and / or one signal inversion device, wherein the signal inversion device is preferably designed as an exclusive-or logic module. First experiments have shown that the proposed structure is particularly suitable for generating a fault signal in a simple, yet effective manner, with which, for example, an emergency shutdown can be realized.

Finally, it is proposed to carry out the converter device such that the error indication comparator has a comparator component, wherein preferably the inverting input of the comparator component is connected to a charge flow reference signal and / or the non-inverting input of the comparator component is connected to an output signal of the integrator. In this context too, what has already been said in advance via comparators or via comparator components proves to be advantageous. The proposed circuit proves to be particularly advantageous for the function of the error indication comparator, in particular in combination.

• 1: ein erstes Ausführungsbeispiel für einen Wandlerkern in einem schematischen Blockschaltbild;
• 2: ein zweites Ausführungsbeispiel für einen Wandlerkern in einem schematischen Blockschaltbild;
• 3: ein Ausführungsbeispiel für einen Wandler mit zwei Integrator-Zweigen und wechselweiser Zweigansteuerung.

In the following the invention will be explained in more detail by means of advantageous embodiments and with reference to the accompanying drawings. Show it:

• 1 a first exemplary embodiment of a converter core in a schematic block diagram;
• 2 a second exemplary embodiment of a converter core in a schematic block diagram;
• 3 FIG. 2 shows an exemplary embodiment of a converter with two integrator branches and alternating two-control.

In 1 is a first conceivable embodiment of a converter core 2 for example, for a charge-flux-frequency converter 1 ("Converter for converting a charge flow into a frequency signal") with two parallel, alternately operated integrator branches 3a . 3b can be used. Even if such operation involves two alternately operated integrator branches 3a . 3b With regard to the extensive exclusion of measurement errors due to dead times is particularly preferred, so are still other uses of the converter core 2 conceivable. The charge flow to be measured 4 is via an input terminal (In) the actual integrator 5 fed. The integrator 5 consists essentially of an operational amplifier 6 and a capacity 7a . 7b , In addition, a reset switch 8th provided with the capacity 7a . 7b can be discharged, leaving the integrator 5 is available for another measuring cycle. In the illustrated embodiment, the capacity 7 in two partial capacities 7a . 7b split, whereby one of the two partial capacities 7b via a switch-on 10 can be switched on as needed. For example, the (always used) first capacity 7a by a capacity of 2.5 pF. This is connected in parallel via the switch 10 switchable second capacity 7b provided by 22.5 pF, so the total capacity 7 of the integrator 5 between 2.5 pF and 25 pF can be adjusted. Through the switching can charge flows 4 with different resolution (required amount of charge to produce an output pulse) are measured, with a higher switched total capacity 7 naturally also the sensitivity of the integrator 5 reduced. In the presently illustrated embodiment, the sensitivity of the converter core is 2 (in addition to the capacity also by the voltage swing of the integrator 5 and the number of counts of the up and down counter 27 is determined) at low capacity (only first capacity 7a switched on) 250 fC, whereas at higher capacity (second capacity 7b switched on) amounts to 2.5 pC. From this and from the speed of construction 2 In contrast, the maximum measurement current essentially results 4 , In the example shown, the height of the maximum measuring current is 4 13 μA or 130 μA. The minimum measuring current is through Leakage currents determined that can not be avoided in the practical realization. In the present structure they are in the order of 100 fA. In the illustrated embodiment, the capacity 7b by a prior programming of the converter core 2 set in advance. In particular, the converter core shown here is 2 (together with other components) in the form of an integrated circuit (ASIC) formed.

Furthermore, in the integrator 5 an input switch 9 to see with the integrator 5 with the charge flow 4 can be connected or can be separated from this. Such an input switch 9 is particularly required when the converter core 2 in a charge-flux-frequency converter 1 with two integrator branches 3a . 3b is used. By alternately switching the input switch 9 that is, the other integrator branch can then be used 3a . 3b used when the "illustrated" transducer core 2 by closing the reset switch 8th is reset, whereby a dead time occurs, while the principle of no measurement can take place.

The charge flow 4 will, how to 1 can take, the inverting input 11 of the operational amplifier 6 fed. The non-inverting input 12 of the operational amplifier 6 in the integrator 5 on the other hand, it becomes a first reference voltage 13a ( V _max ) or a second reference voltage 13b ( V _min ) ("Charge Flow Reference Signal"). The selection of the reference voltage 13 is done by a polarity signal 14 which, for example, via a prior programming of the converter core 2 indicates whether positive or negative charge flows 4 are to be measured (whereby the corresponding selection can also be made by other inputs, in particular by the use of specific, circuit-technical measures). Are negative charge flows 4 becomes the lower (usually negative) second reference voltage 13b ( V _min ), so that the output voltage 15 ( V _ramp ) of the integrator 5 from low voltages (to positive values) can increase. With positive charge flows 4 on the other hand, it becomes the first (typically positive) reference voltage 13a ( V _max ), so that the output voltage 15 of the integrator 5 can drop from a high value.

The output voltage 15 of the integrator 5 becomes the one non-inverting input 17 a comparator 16 (K1) supplied. At the inverting input 18 of the comparator 16 on the other hand, there is a threshold voltage 19 ( V _Thres ), by a digital-to-analog converter 20 is produced. When measuring negative charge flows 4 is the threshold voltage 19 of the comparator 18 initially above the output voltage 15 of the integrator 5 , Once sufficient charge in the capacity 7 integrated, exceeds the output voltage 15 of the integrator 5 finally the threshold voltage 19 and the output voltage 21 The comparator changes to a high value.

Become positive charge flows 4 measured, is the output voltage 15 of the integrator 5 initially at a high value and in particular above the threshold voltage 19 , After a sufficient integration of charge in the capacity 7 will be the output voltage 15 at some point the threshold voltage 19 below. Accordingly, the output voltage changes 21 of the comparator 18 at this time from a high level to a low level.

Since one is independent of the polarity of the charge flow to be measured 4 always want the same output signal, the output signal must 21 of the comparator 16 be selectively inverted. This is the output voltage 21 of the comparator 16 an exclusive-or logic device 22 (XOR gate), in which the other input with the polarity signal 14 connected is.

The thus corrected output signal 23 On the one hand, it is output to further electronic components for further processing (output 24 ; "Out"). Furthermore, the adjusted output signal 23 a pulse shaper 25 fed, which generates a short pulse of fixed length. The pulses thus formed 26 be on the clock input of an up and down counter 27 given. When measuring negative charge flows 4 must be the up and down counter 27 work as an up counter when measuring positive charge flows 4 on the other hand, as a down counter. For this reason, the up and down counter becomes 27 also with the polarity signal 14 provided. The output signal of the up and down counter 27 eventually becomes a digital-to-analog converter 20 supplied to the threshold voltage 19 generated, the threshold voltage 19 in particular, can be increased over several stages before a reset of the integrator 5 is required. The bandwidth of the digital-to-analog converter 20 issued threshold voltages 19 is due to two voltage levels 28 ( V _high . V _low ) ("Digital-to-analogue-span-signal").

Further details on various aspects of the converter core 2 or the charge-flux-frequency converter 1 can in particular the German publication DE 198 41 308 A1 whose disclosure is to be considered as fully incorporated in the disclosure of this application.

For real devices, such as the integrators used here 5 , Comparators 16 , Counters 27 and digital-to-analog converters 20 There are time delay effects that cause the threshold voltage 19 only with a certain delay τ _del (del for delay = delay) is adjusted. This τ _del determines the maximum output frequency of the converter core 2 (or the charge flow frequency converter 1 ). The relationship f _max = 1 / τ _del , whereby also the maximum measurable charge flow 4 I _n , _{max is} determined. Is the charge flow 4 (In) higher than the maximum allowable value I _n , _max , would be during the time τ _del , that of the converter core 2 for adjusting the threshold voltage 19 already requires the next adjustment of the threshold voltage 19 required. This has the consequence that the output voltage 15 of the integrator 5 permanently above the threshold voltage 19 remains (because the output voltage 15 rises faster than the threshold voltage 19 can follow), which usually includes the threshold voltage 19 "Freezes" and not further the output voltage 15 of the integrator 5 follows. The output voltage 15 therefore continues to rise until the operational amplifier 6 of the integrator 5 goes into saturation.

To detect this error condition, another comparator, an error detection comparator 29 , intended. Here is the non-inverting input 30 the error detection comparator 29 with the output voltage 15 of the integrator 5 whereas the inverting input 31 the error detection comparator 29 with one of the two reference voltages 13a . 13b connected (depending on the polarity signal 14 ). In the case of measuring negative charge flows 4 will be the output voltage 15 of the integrator 5 with the first reference voltage 13a , in the case of measuring positive charge flows 4 with the second reference voltage 13b , compared (ie "reverse" to the wiring of the non-inverting input 12 of the operational amplifier 6 in the integrator 5 ). When the output voltage 15 of the integrator 5 about the maximum possible voltage values of the digital-to-analog converter 20 (determined by the voltage levels 28 ), this results in the error detection comparator 29 its output level 32 changes and thus indicates an error condition. As in the case of the comparator 16 (the output signal 21 is provided), depending on the polarity of the charge flow (and thus in dependence on the polarity signal 14 ) requires selective signal inversion. This is also served by an exclusive-or-logic element 22 , The finally generated error signal 33 can be supplied to other electronic components.

In 2 is, also in the form of a schematic diagram, an evolved transducer core 34 shown. The converter core 34 serves for operation in combination with a second (not shown) converter core and thus for example for a charge flow frequency converter 1 as he is in 3 outlined.

The converter core 34 is able to decide automatically whether a positive or a negative charge flow 4 is present. For this purpose, a modified digital-to-analog converter is used 35 , which, in addition to the mean reference voltage 37 (the actual threshold voltage), two more comparison voltages generated (lower reference voltage 36 or upper reference voltage 38 ), preferably by a similar voltage difference from the mean reference voltage 37 are offset. As a design _criterion has proven to be the lower reference voltage (V _Thresl ) 36 with V _Thresl = i × V _LSB (in which V _LSB represents the current voltage interval). The mean reference voltage 37 (V _Thresm ) then results from V _Thresm = V _Thresl +1/2 V _LSB and the upper reference voltage 38 , V _Thresh results from the relationship V _Thresh = V _Threshl + V _LSB ,

These three comparison voltages 36 . 37 . 38 Be suitable for a set of three comparators 39a . 39b . 39c fed. The mean reference voltage 37 (V _Thresm ) is used to decide if the output voltage 15 of the integrator 5 in the upper or lower part of the current voltage interval V _LSB located. If it is in the upper range, it can be expected that the upper reference voltage 38 is exceeded, that is, the mean reference voltage 37 (the actual threshold voltage) must be offset by one interval step up. Accordingly, the, the digital-to-analog converter 35 upstream, up and down counter 27 through the output of the comparator 39b configured to count up. The pulse shapers 25 , the or-logic module 41 and the inverter 40 serve to generate the count clock 26 (Processing the signal).

Is the output voltage 15 of the integrator 5 however, in the lower part of the current voltage interval V _LSB , on the contrary, it is expected that the lower reference voltage 36 is fallen short of. In this case, the mean reference voltage must be 37 (Threshold voltage) are offset by one interval step down. The up and down counter 27 is accordingly configured for downcounting.

The first comparator monitor K1 39a and the third comparator K3 39c , whether the current voltage interval is up (first comparator 39a) or down (third comparator 39c) will leave. If this is the case, it will be over the pulse shaper 25 (if necessary after previous inversion 40 ) generates a pulse of fixed length. The pulse is over one Or logic device 41 to the clock input of the up and down counter 27 given.

Once the up and down counter 27 "Overflows" (either up or down; the transducer core 34 must then be reset), the charge flow measurement is taken over by the second converter core. For this purpose, a switching signal is used 42 , At the same time in the converter 34 recognized "counting direction" in the form of a polarity signal 14 transmitted to the other converter core so that it can be preinitialized. Accordingly, the other transducer according to the idea as already described in relation to in 1 illustrated converter core 2 described, pre-initialized.

In 3 is finally shown schematically as a charge-flux-frequency converter 1 with two integrator branches 3a (for example, transducer cores 1 . 34 according to the type of 1 or from 2 ; other designs are conceivable) can be constructed. For the sake of explanation, the explanations given in connection with in 1 illustrated transformer cores 2 used reference numerals, without being limiting.

Once through the relevant integrator branch 3a . 3b (in this case consisting of integrator 5 and comparator 16 ) a (cleaned) output signal 23 is present, this is an OR logic device 41 both a tap 43 as well as a D flip flop 44 fed. Because of the signal in question 23 changes the D flip flop 44 its state, that is, the signals at the outputs Q and / Q are respectively inverted. This will cause the previously opened input switch 9 closed and the previously closed input switch 9 open. Parallel to this is the "fully loaded" integrator 5 by closing a reset switch 8th reset to zero. Preferably, the resetting of the relevant integrator takes place immediately and over a certain period of time (accordingly, a certain amount of time passes until the reset signal at the reset switch 8th is canceled again; a typical value for this is 50 ns). Delay elements are used to generate this time delay 45 ,

Details of the "alternate parallel operation" of the integrator branches 3a . 3b in charge-frequency converter, for example, the already mentioned German Offenlegungsschrift DE 198 41 308 A1 be removed.

Further advantages, features and further developments of the proposed invention are the German patent application, which was deposited at the same day under the applicant's file number P 434-b-DE and entitled "charge flow frequency converter with error indicator" at the German Patent and Trademark Office, refer to. The disclosure of the local registration documents is incorporated by cross-reference completely in the disclosure of the present application.

LIST OF REFERENCE NUMBERS

1.

Flow of charge-to-frequency converter

Second

transformer core

Third

Integrator branch

4th

flow of charge

5th

integrator

6th

operational amplifiers

7th

capacity

8th.

Reset switch

9th

input switch

10th

Zuschalter

11th

Inverting entrance

12th

Non-inverting input

13th

reference voltage

14th

polarity signal

15th

output voltage

16th

comparator

17th

Non-inverting input

18th

Inverting entrance

19th

threshold voltage

20th

Digital to analog converter

21st

output voltage

22nd

Exclusive OR logic device

23rd

Adjusted output voltage

24th

output

25th

pulse shaper

26th

Pulse

27th

Up and down counter

28th

voltage level

29th

Error detection comparator

30th

Non-inverting input

31st

Inverting entrance

32nd

output voltage

33rd

error signal

34th

transformer core

35th

Digital to analog converter

36th

Lower reference voltage

37th

Mean reference voltage

38th

Upper comparison voltage

39th

comparator

40th

inverter

41st

Or logic device

42nd

switching signal

43rd

tap

44th

D flip-flop

45th

delay element

Claims (15)

A converter device (2, 34) for converting a charge flow (4) into a frequency signal (23), comprising at least one integrator (5, 5a, 5b) and at least one comparator (16, 16a, 16b, 39a, 39b, 39c) at least one integrator (5, 5a, 5b) and at least one comparator (16, 16a, 16b, 39a, 39b, 39c) are connected in series and the comparator (16, 16a, 16b, 39a, 39b, 39c) when an integrated charge flow is exceeded relative to a threshold voltage (19) and / or a comparison voltage (36, 37, 38) emits a signal (23), characterized by at least one charge flow direction selection means, with which the converter device (2, 34) selectively to a positive or a negative charge flow (4) can be set. Converter device (2, 34) after Claim 1 , characterized by at least two integrators (5a, 5b) connected in parallel with one another, which are alternately charged with the charge flow (4). Converter device (2, 34) after Claim 1 or 2 , characterized in that the charge flow direction selection means, the integrator and / or the comparator (16, 39) preferably mutually supplied with in each case one of two charge flux reference voltages (13a, 13b). Converter device (2, 34) according to one of the preceding claims, characterized in that the charge flow direction selection device comprises at least one changeover switch device. Converter device (2, 34) according to one of the preceding claims, characterized in that the comparator (16) is followed by a preferably conditional signal inversion device (22), in particular an exclusive-OR logic device (22), which preferably depends on the Position of the charge flow direction selection means inverting acts. Converter device (2, 34) according to one of the preceding claims, characterized in that the integrator (5) comprises an operational amplifier (6) and in particular the charge flow (4) with the inverting input (11) of the operational amplifier (6) and / or the charge-flux reference voltage (13a, 13b) is connected to the non-inverting input (12) of the operational amplifier (6). Converter device (2, 34) according to one of the preceding claims, characterized in that the comparator (16, 39) has a comparator component (16, 39) and in particular the output signal (15) of the integrator (5) with the non-inverting input (16). 17) of the comparator component (16) and / or a threshold voltage (19) and / or a comparison voltage (36, 37, 38) is connected to the inverting input (18) of the comparator component (16, 39). Converter device (2, 34) according to one of the preceding claims, characterized in that the output signal (21) of the comparator (16, 39) and / or the signal inversion device (22, 40) is supplied to a pulse shaping device (25). Converter device (2, 34) according to one of the preceding claims, in particular according to Claim 8 characterized by a digital counter (27) and / or a digital-to-analog converter (20, 35), which can supply the comparator (16, 39) different threshold voltages (19) and / or comparison voltages (36, 37, 38), in particular as a function of an output value (23) of the comparator (16, 39), preferably in dependence on a count value of the counter (27). Converter device (2, 34) according to one of the preceding claims, in particular according to Claim 9 characterized by a digital-to-analogue-to-wedge signal input means. Converter device (2, 34) according to one of the preceding claims, in particular according to Claim 2 characterized by reset signal output means (45a, 45b) which resets one integrator (5) and preferably activates another integrator (5). Converter device (2, 34) according to one of the preceding claims, characterized by at least one self-adjusting charge flow direction selection device. Converter device (2, 34) according to one of the preceding claims, characterized by at least one frequency-exceeding signal output device (29). Converter device (2, 34) after Claim 12 characterized in that the frequency-overflow signal output device (29) has at least one error indication comparator (29) and / or signal inversion device (22), wherein the signal inversion device (22) is preferably in the form of an exclusive-OR logic device ( 22) is formed. Converter device (2, 34) after Claim 14 , characterized in that the error indication comparator (29) comprises a comparator component (29), wherein preferably the inverting input (31) of the comparator component (29) with a charge flow reference voltage (13a, 13b) and / or the non-inverting input (17) of the comparator component (29) is connected to an output signal (15) of the integrator (5).

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