• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    Conventional analog and digital charge amplifiers, for converting a charge output from a piezoelectric sensor into a proportional voltage, require analog integration inherent in a drift in the output signal. To avoid this, a digital charge amplifier (1) is proposed in which, depending on the output of a comparator (5), a positive or negative constant feedback current (if) is fed back to the input (2) and the input current (ie) is compensated wherein a counter (7) detects the time period during which a feedback current (if) flows.
    公开号:AT511664A2
    申请号:T504582012
    申请日:2012-10-17
    公开日:2013-01-15
    发明作者:
    申请人:Avl List Gmbh；
    IPC主号:
    专利说明:

    Printed: 18-10-2012 E014.1
    10 2012/50458 AV-3502 AT
    Digital charge amplifier
    The subject invention relates to a digital charge amplifier having an analog input to which an input voltage is applied and an input current flows and having a digital output, and a method for digitizing an analog signal fed to a charge amplifier at an analog input.
    Piezoelectric sensors are typically operated with charge amplifiers that convert the charge output from the piezoelectric sensor into a proportional electrical voltage. As charge amplifiers, operational amplifiers with capacitive feedback are often used which operate as integrators. The disadvantage of such charge amplifiers for a piezoelectric sensor is known to be that the charge delivered by the sensor can be very small, whereby the use of low-noise special cables, which are expensive, becomes necessary for connecting the sensor and charge amplifier. Due to the high input impedance of the charge amplifier, the transmission path is also sensitive to electromagnetic fields, which limits the cable lengths to a few 15 meters. Another disadvantage of such charge amplifiers is the inherent drift in the output signal due to analog integration, for example due to the leakage currents at the input, which necessitates drift compensation.
    Alternatively, impedance converters are known which convert the high impedance signal of the piezoelectric sensor into a low impedance voltage signal which can then be transmitted with low loss over long lines. The impedance converter is often integrated in the sensor, but this limits the possible use. For example, For example, such sensors with integrated electronics can not be used in high pressure and / or temperature environments, e.g. be used as a pressure transducer in the cylinder of an internal combustion engine. In addition to the analog charge amplifiers, digital charge amplifiers have also become known which digitally output the value of the charge emitted by the sensor or of a voltage proportional thereto. However, the input stage still remains analog and only the integrated input signal is digitized and output as a digital value. The above-mentioned problems of the analog charge amplifier are retained. 30 Charge amplifiers based on a Sigma-Delta analogue digital converter have also become known. Such a transducer is used e.g. from WO 2009/062494 A1, EP 1 345 330 A2 or GB 2 292 028 A. The digital output of the converter is fed back to the input via a digital-to-analog converter. The difference between input current and feedback current is integrated, quantized and sampled at a high sampling rate. -1- T7-10-2012 E014.1
    Printed: 18-10-2012 10 2012/50458
    AV-3502 AT tet. The bitstream at the output represents a digital representation of the input voltage.
    At the output may also be provided a digital filter. However, as before, an analog integration by means of a capacitance is required at the input, which is why the associated problems can not be remedied thereby. It is therefore an object of the present invention to provide a digital charge amplifier and a method for digitizing an analog signal, which brings about an improvement in the above-mentioned disadvantages.
    This object is achieved according to the invention by providing a comparator which compares the input voltage with a reference potential and the output of the comparator drives a feedback current source, the feedback current source producing a positive or negative constant feedback current depending on the output of the comparator Input is fed back and compensates for the input current, wherein a counter is provided, whose counting direction is determined by the output of the comparator and the output of the counter is provided as a digital output 15 of the digital charge amplifier.
    At the input of the comparator, or at the input of the charge amplifier, the feedback of a feedback current controlled by the comparator generates a virtual short circuit, namely that the input current is compensated by the feedback current. In this case, the feedback quantity corresponding to the amount of charge emitted by the piezoelectric sensor is not set by the current intensity as in conventional analog and digital charge amplifiers, but by the time during which a negative or positive reference current is fed back. The time duration is determined by the output of the comparator. In this way, it is achieved that the feedback amount of charge is proportional to a period of time that can be measured in a simple manner with the aid of a counter. The output of the counter is thus dependent on the input current and proportional to the charge delivered by the piezoelectric sensor. The counting thus corresponds to the temporal integration of the input current. The sought measurement result is therefore digitally available as a count value without having to carry out an analog integration. In an advantageous simple embodiment, the comparator controls a control logic, which in turn drives the feedback power source. It is particularly easy when the control logic generates counts for the counter.
    In a further advantageous simple implementation of the invention, reference potential for the comparator, the reference potential of the input, in particular ground, is provided. -2-
    Printed: 18-10-2012 E014.1 10 2012/50458
    AV-3502 AT
    If a reference potential generating unit is provided in which a controller is implemented, which eliminates the time average of the feedback current, or a proportional thereto feedback voltage and as a manipulated variable generates the reference potential for the comparator, can be easily harmful effect of offset-5 voltage and eliminate bias current of the input stage and one obtains so a virtually drift-free charge amplifier.
    If a window comparator is used as the comparator, the idle state, that is to say the state in which the sensor emits no charge, can also be detected in an advantageous manner. In order to make the charge amplifier more flexibly replaceable, a sensitivity input, via which the sensitivity of the feedback current source can be set, and / or a preset input, which can be set via a defined starting point of the counter, can be provided on the charge amplifier.
    The digital uncertainty and possible cross sensitivities between the analog and the 15 digital circuit part can be reduced if the feedback current is modulated in time with a reference frequency source.
    The subject invention will be explained in more detail below with reference to Figures 1 to 5, which show schematically, by way of example and not limitation, advantageous embodiments of the invention. FIG. 1 shows a block diagram of the charge amplifier according to the invention, FIG.
    2 is a more detailed block diagram of the charge amplifier according to the invention,
    3 shows a simple implementation of the charge amplifier according to the invention,
    4 shows an implementation of the charge comparator with window comparator according to the invention, and FIG. 5 shows an implementation of the charge amplifier according to the invention with modulated feedback current.
    In FIG. 1, a digital charge amplifier 2 according to the invention is connected to a piezoelectric sensor 1 via an analog input 2. At a digital output 3 of the charge amplifier 2, a digital signal is output, which is proportional to the output from 30 piezoelectric sensor 1 charge. For this purpose, a comparator 5 is provided in the charge amplifier 2, which compares the input voltage ue with a reference voltage u0. As the reference voltage u0, hereby. the ground potential of the piezoelectric sensor 1 is provided. The output of the comparator 5 controls, on the one hand, a feedback current source 6 and also a counter 7. The feedback current source 6 generates a -3-
    Printed: 18-10-2012 E014.1 10 2012/50458
    AV-3502 AT Feedback current if, which compensates the input current ie and thus generates a virtual short circuit at the input. The time period during which a positive or negative feedback current (depending on the output of the comparator 5) is fed back, is detected by the counter 7. The counting direction of the counter 7 is determined by the presence of the feedback current if. The count of the counter 7 is thus dependent on the feedback current if and thus also of the input current ie and thus proportional to the output from the piezoelectric sensor 1 charge. The basic idea is therefore that the required integration of the input current ie not analogously by means of a capacitance, but digitally and therefore without drift durchzufüh by means of a counter 7 ren.
    The function of the charge amplifier 1 according to the invention will now be explained in more detail with reference to an advantageous embodiment according to FIG. The input stage of the charge amplifier 1 is formed by a comparator 5, which compares the input voltage ue with a reference potential uo and its result - characterized e.g. through the states larger, greater than equal, smaller, smaller than equal - outputs to a control logic 10. The virtual short at the input targeted for current measurement is here shown e.g. achieved in that in the feedback current source 6 with a reference current generation unit 12 from a reference voltage source 11, a constant feedback current if is generated, as will be described in more detail below. For this purpose, a sensitivity input 13 for presetting or for setting a sensitivity E can also be provided on the charge amplifier 1. The control logic 10 controls the feedback current source 6 so that the input current ie is being compensated. In this case, in contrast to the conventional charge amplifier, the feedback feedback current if (or the feedback charge quantity) is not set by the instantaneous value of the current, 25 but by the time during which a negative or positive feedback current if constant and defined current is switched on. The current strength of the feedback current if is given by the reference voltage uR and the set sensitivity E. The time period during which a feedback current if is generated is determined by the control signals derived from the result of the comparator 5. In this way 30 it is achieved that the feedback quantity of charge is proportional to a period of time which can be measured in a simple manner by means of a reference frequency fR which is generated in a reference frequency source 14 and a counter 7. For this purpose, 5 counting pulses are generated from the clock signal of the reference frequency source 14 and from the result signals of the comparator, which are counted by the counter 7. The counter 7 is advantageously able to count both upwards and downwards. This counting corresponds to the time integration of the input current ie and the instantaneous counting result is therefore proportional to the amount of charge which is emitted by the piezoelectric sensor 1. This is -4-
    Printed: 18-10-2012 E014.1 10 2012/50458
    AV-3502 AT the sought reading in digital form available and can be output as a digital value at the digital output 4 of the charge amplifier 1.
    To set a defined starting point, a preset input 15 can be provided at the charge amplifier 1, via which the counter 7 can be reset and / or set to a certain counter reading. This can also be seen as a definition of an integration constant and used, for example, for setting the digital output signal to a measurement value of the piezoelectric sensor known at certain times.
    The reference potential u0 for the comparator 5 may be generated in a reference potential generation unit 16. The reference potential Uo at the input of the comparator 5 can, as already mentioned above, in the simplest case the reference potential of the input line or the piezoelectric sensor 1, that is e.g. Mass, his. However, it is also possible to eliminate the harmful effect of offset voltage and bias current of the input stage via a regulation of u0. One thus obtains a practically drift-free charge amplifier 15 1. To generate the reference potential u0, it is expedient to use an integral controller which can also have proportional components. The controller has the task of the temporal average value of the feedback current if, or a proportional thereto proportional feedback voltage ur, disappear. For this purpose, it compares the actual value of the feedback voltage uf with a reference value, e.g. is given by the reference potential of the input line 20 or the piezoelectric sensor 1. From the detected deviation, it generates the reference potential u0 for the comparator according to its control characteristic as manipulated variable.
    A very simple implementation of the charge amplifier 1 according to the invention is shown in FIG. The comparator 5 provides only two states, namely greater than or equal to 25 less-equal, which sets the counting direction of the counter 7. The control logic 10 is a simple switch whose position causes a positive or negative feedback current if via a simple differential amplifier. The idle state is not detected by the comparator 5, which is why in the idle state constantly between positive and negative feedback current if and vice versa. The reference potential u0 is set here in dependence on the feedback voltage uf via an IP controller, in the form of an integrator with a proportional component.
    4 shows a charge amplifier 1 according to the invention with window comparator 20 and optional preamplifier 21 as comparator 5. Thus, the idle state can also be detected, in which no feedback current if is generated and in which no counting pulses are emitted.
    Printed: 18-10-2012 E014.1
    10 2012/50458 AV-3502 AT for counter 7 are generated. Depending on the output of the comparator 5, the counter 7 counts up or down or not at all.
    In the embodiment according to FIG. 5, the negative and positive feedback current if is modulated at the rate of the reference frequency fR, here pulse width modulated (PWM). At the same time, the illustrated circuit ensures that the reference voltage uR and thus also the feedback current if are symmetrical, ie are zero in the time average. As a result, compared with the circuits according to FIGS. 3 or 4, the digital uncertainty and possible cross sensitivities between the analog and the digital circuit part can be reduced. io Single or all components of the digital charge amplifier according to the invention, z. Of course, the counter or drift control described in FIGS. 1 to 5 on the basis of hardware can also be realized as software, e.g. on a microprocessor, a digital signal processor (DSP) or a programmable logic device. 15
    -6-
    权利要求:
    Claims (11)
    [1]
    Printed: 18-10-2012 E014.1 10 2012/50458 AV-3502 AT Claims 1. A digital charge amplifier having an analogue input (2) to which an input voltage (ue) is applied and an input current (ie) flows, and a digital input amplifier digital output (3), 5, characterized in that a comparator (5) is provided, which compares the input voltage (Ue) with a reference potential (u0), that the output of the comparator (5) drives a feedback current source (6), wherein the Feedback current source (6) in response to the output of the comparator (5) generates a positive or negative constant feedback current (i (), which is fed back to the input (2) and which compensates the input 10 (ie) and that a counter ( 7) is provided, whose counting direction is determined by the output of the comparator (5) and the output of the counter (7) as a digital output (3) of the digital charge amplifier (1) is provided.
    [2]
    2. Digital charge amplifier according to claim 1, characterized in that the comparator (5) controls a control logic (10) which controls the feedback current source (6) to 15.
    [3]
    3. Digital charge amplifier according to claim 2, characterized in that the control logic (10) generates counting pulses for the counter (7).
    [4]
    4. Digital charge amplifier according to one of claims 1 to 3, characterized in that as reference potential (u0) for the comparator (5), the reference potential of the input 20, in particular ground, is provided.
    [5]
    5. Digital charge amplifier according to one of claims 1 to 3, characterized in that a reference potential generating unit (16) is provided, in which a controller is implemented, the time average of the feedback current (if), or a proportional thereto feedback voltage (uf) , eliminated and as a manipulated variable the reference 25 potential (u0) for the comparator (5) generated.
    [6]
    6. Digital charge amplifier according to one of claims 1 to 5, characterized in that a window comparator is provided as the comparator (5).
    [7]
    7. Digital charge amplifier according to one of claims 1 to 6, characterized in that the charge amplifier (1) has a sensitivity input (13) is provided, via which the sensitivity (E) of the feedback current source (6) is adjustable. -7- Printed: 18-10-2012 E014.1 10 2012/50458 AV-3502 AT
    [8]
    8. Digital charge amplifier according to one of claims 1 to 7, characterized in that the charge amplifier (1) has a preset input (15) is provided, via which a defined starting point of the counter (7) is adjustable,
    [9]
    9. Digital charge amplifier according to one of claims 1 to 8, characterized 5 records that the feedback current (ie) is modulated in time with a reference frequency source (14).
    [10]
    10. A method of digitizing an analog signal which is fed to a charge amplifier (1) at an analog input (2), characterized in that the analog input voltage (ue) in a comparator (5) with respect to a reference potential (u0) 10 is compared in that the output of the comparator (2) is used to drive a feedback current source (6) which, depending on the output of the comparator (5), generates a positive or negative constant feedback current (if) which is fed back to the input (2) and Input current (ie) compensated, and that the period during which a positive or negative feedback current (if) is fed back depending on the output of Kompa 15 erator (5), by a counter (7) whose counting direction by the sign of the feedback current (IF) is determined, wherein the output of the counter (7) as a digital output (3) of the digital charge amplifier (1) is used.
    [11]
    11. The method according to claim 10, characterized in that the feedback current (if) is modulated in time with a reference frequency source (14). 20

    17-10 * 2012
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    同族专利:
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    引用文献:
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    EP0253016B1|1986-07-18|1992-02-26|Kistler Instrumente AG|Charge amplifier circuit|
    US5274375A|1992-04-17|1993-12-28|Crystal Semiconductor Corporation|Delta-sigma modulator for an analog-to-digital converter with low thermal noise performance|
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    法律状态:
    优先权:
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    ATA50458/2012A|AT511664B1|2012-10-17|2012-10-17|Digital charge amplifier|ATA50458/2012A| AT511664B1|2012-10-17|2012-10-17|Digital charge amplifier|
    DE112013005030.7T| DE112013005030A5|2012-10-17|2013-10-16|Digital charge amplifier|
    PCT/EP2013/071614| WO2014060469A1|2012-10-17|2013-10-16|Digital charge amplifier|
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