WO2005071836A1 - Low-pass circuit - Google Patents

Low-pass circuit Download PDF

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Publication number
WO2005071836A1
WO2005071836A1 PCT/DE2004/002536 DE2004002536W WO2005071836A1 WO 2005071836 A1 WO2005071836 A1 WO 2005071836A1 DE 2004002536 W DE2004002536 W DE 2004002536W WO 2005071836 A1 WO2005071836 A1 WO 2005071836A1
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WO
WIPO (PCT)
Prior art keywords
low
frequency
pass circuit
pass
pulse width
Prior art date
Application number
PCT/DE2004/002536
Other languages
German (de)
French (fr)
Inventor
Sascha Kopplin
Original Assignee
Robert Bosch Gmbh
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Robert Bosch Gmbh filed Critical Robert Bosch Gmbh
Publication of WO2005071836A1 publication Critical patent/WO2005071836A1/en

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H19/00—Networks using time-varying elements, e.g. N-path filters
    • H03H19/008—Networks using time-varying elements, e.g. N-path filters with variable switch closing time
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
    • H03H7/01—Frequency selective two-port networks
    • H03H7/12—Bandpass or bandstop filters with adjustable bandwidth and fixed centre frequency

Definitions

  • the invention is based on a low-pass circuit according to the type of the independent claim.
  • a low-pass filter with a variable cut-off frequency is already known from US Pat. No. 6,134,282. A change in a control frequency is used for this.
  • the low-pass circuit according to the invention with the features of the independent claim has the advantage that the change in the cut-off frequency is now achieved by means of pulse width modulation. This is a considerably simpler solution, since no frequency-tunable element now has to be provided. This means that simpler components can be used.
  • tantalum capacitors which have higher capacitance values, have a greater tolerance over the service life and also a not insignificant temperature dependence. It is therefore possible to use smaller capacitances with the low-pass circuit according to the invention by using the pulse width modulation, so that a lower tolerance and an improvement in the temperature dependency are now made possible.
  • the measures specified in the dependent claim allow advantageous improvements to the low-pass circuit specified in the independent claim. It is particularly advantageous that a switch is provided for pulse width modulation. This switch is advantageously implemented by transistors. For example, field effect transistors can be used for this.
  • FIG. 1 shows a circuit diagram of a conventional low pass
  • FIG. 2 shows a circuit diagram of the low pass circuit according to the invention
  • FIG. 3 shows a comparison of the conventional low pass circuit and the low pass circuit according to the invention.
  • Low-pass filters are particularly popular in vehicle electronics for filtering high-frequency signals.
  • the output signals from acceleration sensors are subjected to low-pass filtering for smoothing.
  • the component values of the resistor and capacitor used would have to be high, since these values are in the denominator in the equation for determining the cutoff frequency.
  • FIG. 2 now explains the solution according to the invention.
  • a switch S is now provided between the signal source Ue and the resistor, which is opened and closed by a pulse width modulated signal Ust.
  • the resistor R is in turn connected on its other side to the output terminal Ua and the capacitor C, which in turn is then connected to the other end of the signal source Ue.
  • the switch S is therefore controlled via the clocked signal Ust.
  • the required pulse width t_Pw depends on the desired capacity ratio.
  • the quantity t_Pw is related to a second, so that this quantity is dimensionless.
  • the frequency of the control signal Ust must be much higher than the cut-off frequency of the low-pass filter from FIG. 1. This cutoff frequency corresponds to the values given by the values of the components R and C.
  • the limit frequency can be changed by varying the pulse width.
  • switch S Various components that can perform a switching function can be used as switch S. In addition to field effect and biopolar transistors, this also includes mechanical switches that are suitable for implementing the corresponding pulse width modulation.
  • FIG. 3 shows the output signals of the low-pass filter according to FIG. 1 and of the modified low-pass filter according to the invention with a pulse width of t_Pw ⁇ 0.1.
  • Curve 30 shows the input signal
  • curve 32 the output signal of the low-pass filter according to FIG. 1
  • curve 31 shows the output signal of the low-pass filter according to the invention.
  • the comparison of the two output signals Ua shows that the output signal of the low-pass filter 31 according to the invention has a significantly lower cut-off frequency and thus filters out higher-frequency signal components better than the conventional low-pass filter can. That will decrease Test ratio without the switching frequency, then the noise component of the output signal Ua increases.
  • the control of the switch S can be implemented, for example, by a computer circuit.
  • the Cutoff frequency is changed by the pulse width experiencing a change accordingly.
  • the low-pass filter for example, for low-pass filtering acceleration signals
  • the cut-off frequency can be increased or decreased depending on the signal analysis in order to obtain better information about the signal.

Abstract

The invention relates to a low-pass circuit having a variable cutoff frequency. The low-pass circuit is characterized in that it varies the cutoff frequency by way of pulse-width modulation.

Description

Tiefpassschaltung Low-pass circuit
Stand der TechnikState of the art
Die Erfindung geht aus von einer Tiefpassschaltung nach der Gattung des unabhängigen Patentanspruchs.The invention is based on a low-pass circuit according to the type of the independent claim.
Aus US-6, 134,282 ist bereits ein Tiefpass mit einer veränderbaren Grenzfrequenz bekannt. Dazu wird eine Änderung einer Steuerfrequenz verwendet.A low-pass filter with a variable cut-off frequency is already known from US Pat. No. 6,134,282. A change in a control frequency is used for this.
Vorteile der ErfindungAdvantages of the invention
Die erfindungsgemäße Tiefpassschaltung mit den Merkmalen des unabhängigen Patentanspruchs hat demgegenüber den Vorteil, dass die Veränderung der Grenzfrequenz nunmehr mittels einer Pulsweitenmodulation erreicht wird. Dies ist eine erheblich einfachere Lösung, da nun kein frequenzdurchstimmbares Element vorgesehen sein muss. Damit können einfachere Komponenten verwendet werden. Insbesondere ist es mit der erfindungsgemäßen Tiefpassschaltung möglich, kleinere Kapazitäten zur Erreichung niedriger Grenzfrequenzen einzusetzen. Normalerweise wäre bei einer niedrigen Eckfrequenz der Einsatz hoher Widerstands- oder Kapazitätswerte notwendig. Insbesondere beim Einsatz in der Fahrzeugelektronik wird jedoch die Verwendung von hochohmigen Widerständen vermieden, da Feuchtigkeit und Verschmutzungen zu hochohmigen Nebenschlüssen führen können ,die die Funktion der Schaltung negativ beeinflussen. Die Verwendung größerer Kapazitätswerte erhöht die Kosten. Zudem haben Tantalkondensatoren, die höhere Kapazitätswerte aufweisen, eine größere Toleranz über der Lebensdauer und auch eine nicht zu vernachlässigende Temperaturabhängigkeit. Daher kann mit der erfindungsgemäßen Tiefpassschaltung durch die Verwendung der Pulsweitenmodulation auf kleinere Kapazitäten zurückgegriffen werden, so dass nunmehr eine geringere Toleranz und eine Verbesserung der Temperaturabhängigkeit ermöglicht wird.The low-pass circuit according to the invention with the features of the independent claim has the advantage that the change in the cut-off frequency is now achieved by means of pulse width modulation. This is a considerably simpler solution, since no frequency-tunable element now has to be provided. This means that simpler components can be used. In particular, it is possible with the low-pass circuit according to the invention to use smaller capacitances to achieve lower cut-off frequencies. Normally, with a low corner frequency, the use of high resistance or capacitance values would be necessary. In particular when used in vehicle electronics, however, the use of high-impedance resistors is avoided, since moisture and dirt can lead to high-impedance shunts, which negatively influence the function of the circuit. Using larger capacities increases costs. In addition, tantalum capacitors, which have higher capacitance values, have a greater tolerance over the service life and also a not insignificant temperature dependence. It is therefore possible to use smaller capacitances with the low-pass circuit according to the invention by using the pulse width modulation, so that a lower tolerance and an improvement in the temperature dependency are now made possible.
Durch die im abhängigen Anspruch angegebenen Maßnahmen sind vorteilhafte Verbesserungen der im unabhängigen Patentanspruch angegebenen Tiefpassschaltung möglich. Besonders vorteilhaft ist, dass zur Pulsweitenmodulation ein Schalter vorgesehen ist. Dieser Schalter wird vorteilhafter Weise durch Transistoren realisiert. Dazu können beispielsweise Feldeffekttransistoren eingesetzt werden.The measures specified in the dependent claim allow advantageous improvements to the low-pass circuit specified in the independent claim. It is particularly advantageous that a switch is provided for pulse width modulation. This switch is advantageously implemented by transistors. For example, field effect transistors can be used for this.
Zeichnungdrawing
Ausführungsbeispiele der Erfindung sind in der Zeichnung dargestellt und werden in der nachfolgenden Beschreibung näher erläutert.Embodiments of the invention are shown in the drawing and are explained in more detail in the following description.
Es zeigen Figur 1 ein Schaltbild eines herkömmlichen Tiefpasses, Figur 2 ein Schaltbild der erfindungsgemäßen Tiefpassschaltung und Figur 3 ein Vergleich der herkömmlichen Tiefpassschaltung und der erfindungsgemäßen Tiefpassschaltung.FIG. 1 shows a circuit diagram of a conventional low pass, FIG. 2 shows a circuit diagram of the low pass circuit according to the invention, and FIG. 3 shows a comparison of the conventional low pass circuit and the low pass circuit according to the invention.
Beschreibungdescription
Tiefpassfilter finden insbesondere in der Fahrzeugelektronik zur Filterung hochfrequenter Signale eine weiter Verbreitung. Insbesondere die Ausgangssignale von Beschleunigungssensoren werden einer Tiefpassfilterung zur Glättung unterzogen. Um dabei möglichst geringe Grenzfrequenzen zu realisieren, müssten die Bauteilwerte des verwendeten Widerstands und des Kondensators hoch ausfallen, da diese Wert in der Gleichung zur Bestimmung der Grenzfrequenz im Nenner stehen. Dies verbietet sich jedoch aus den oben genannten Gründen. Folglich wird erfindungsgemäß vorgeschlagen, eine veränderbare Grenzfrequenz dadurch zu erreichen, dass eine Pulsweitemodulation realisiert wird, mit der die hohen Bauteilwerte simuliert werden. Figur 1 zeigt ein Tiefpassfilter erster Ordnung mit einer Signalquelle Ue, einem Widerstand R, der in Reihe zur Signalquelle Ue geschaltet ist, wobei an einer anderen Seite des Widerstands R ein Ausgangsschluss Ua und ein Kondensator C geschaltet ist. Der Kondensator C ist an seiner anderen Seite mit dem anderen Ende der Signalquelle Ue verbunden. Damit ist ein herkömmlicher Tiefpass erster Ordnung realisiert. Die Grenzfrequenz berechnet sich aus f_g = 1/(2 • π ■ R ■ C) .Low-pass filters are particularly popular in vehicle electronics for filtering high-frequency signals. In particular, the output signals from acceleration sensors are subjected to low-pass filtering for smoothing. In order to achieve the lowest possible cutoff frequencies, the component values of the resistor and capacitor used would have to be high, since these values are in the denominator in the equation for determining the cutoff frequency. However, this is prohibited for the reasons mentioned above. It is therefore proposed according to the invention to achieve a variable cut-off frequency by realizing pulse width modulation with which the high component values are simulated. FIG. 1 shows a low-pass filter of the first order with a signal source Ue, a resistor R, which is connected in series with the signal source Ue, an output terminal Ua and a capacitor C being connected on another side of the resistor R. The capacitor C is connected on its other side to the other end of the signal source Ue. A conventional first order low-pass filter is thus implemented. The limit frequency is calculated from f_g = 1 / (2 • π ■ R ■ C).
Figur 2 erläutert nun die- erfϊndungsgemäße Lösung. Nun ist zwischen der Signalquelle Ue und dem Widerstand ein Schalter S vorgesehen, der durch einen Pulsweiten moduliertes Signal Ust geöffnet und geschlossen wird. Der Widerstand R ist wiederum an seiner anderen Seite mit dem Ausgangsschluss Ua und dem Kondensator C verbunden, der dann wiederum an das andere Ende der Signalquelle Ue angeschlossen ist. Der Schalter S wird demnach über das getaktete Signal Ust gesteuert. Die erforderliche Pulsweite t_Pw ist abhängig vom gewünschten Kapazitätsverhältnis. Die Grenzfrequenz berechnet sich zu f_g = \l(2 - π ■ R - t _PW - C) . Dabei ist die Größe t_Pw auf eine Sekunde bezogen, so dass diese Größe dimensionslos ist. Die Frequenz des Steuersignals Ust muss viel Größer als die Grenzfrequenz des Tiefpassfilters aus Figur 1 sein. Diese Grenzfrequenz entspricht den Größen, die durch die Werte der Komponenten R und C gegeben sind. Durch eine Variation der Pulsweite lässt sich die Grenzfrequenz ändern.FIG. 2 now explains the solution according to the invention. A switch S is now provided between the signal source Ue and the resistor, which is opened and closed by a pulse width modulated signal Ust. The resistor R is in turn connected on its other side to the output terminal Ua and the capacitor C, which in turn is then connected to the other end of the signal source Ue. The switch S is therefore controlled via the clocked signal Ust. The required pulse width t_Pw depends on the desired capacity ratio. The cutoff frequency is calculated as f_g = \ l (2 - π ■ R - t _PW - C). The quantity t_Pw is related to a second, so that this quantity is dimensionless. The frequency of the control signal Ust must be much higher than the cut-off frequency of the low-pass filter from FIG. 1. This cutoff frequency corresponds to the values given by the values of the components R and C. The limit frequency can be changed by varying the pulse width.
Als Schalter S können verschiedene Komponenten, die eine Schaltfunktion ausführen können, eingesetzt werden. Dazu zählen neben Feldeffekt- und Biopolartransistoren auch mechanische Schalter die zur Realisierung der entsprechenden Pulsweitenmodulation geeignet sind.Various components that can perform a switching function can be used as switch S. In addition to field effect and biopolar transistors, this also includes mechanical switches that are suitable for implementing the corresponding pulse width modulation.
Figur 3 zeigt die Ausgangssignale des Tiefpassfilters gemäß Figur 1 und des modifizierten erfindungsgemäßen Tiefpassfilters mit einer Pulsweite von t_Pw ~ 0,1. Dabei ist durch die Kurve 30 das Eingangssignal, die Kurve 32 das Ausgangssignal des Tiefpassfilters gemäß Figur 1 gezeigt und durch die Kurve 31 das Ausgangssignal des erfindungsgemäßen Tiefpassfilters. Der Vergleich der beiden Ausgangssignale Ua zeigt, dass das Ausgangssignal des erfindungsgemäßen Tiefpassfilters 31 eine erheblich geringere Grenzfrequenz aufweist und damit höherfrequente Signalanteile besser herausfiltert, als das der herkömmliche Tiefpassfilter vermag. Verringert sich das Testverhältnis ohne die Schaltfrequenz, dann erhöht sich jedoch der Rauschanteil des Ausgangssignals Ua.FIG. 3 shows the output signals of the low-pass filter according to FIG. 1 and of the modified low-pass filter according to the invention with a pulse width of t_Pw ~ 0.1. Curve 30 shows the input signal, curve 32 the output signal of the low-pass filter according to FIG. 1, and curve 31 shows the output signal of the low-pass filter according to the invention. The comparison of the two output signals Ua shows that the output signal of the low-pass filter 31 according to the invention has a significantly lower cut-off frequency and thus filters out higher-frequency signal components better than the conventional low-pass filter can. That will decrease Test ratio without the switching frequency, then the noise component of the output signal Ua increases.
Die Ansteuerung des Schalters S kann beispielsweise durch eine Rechnerschaltung realisiert sein. Dazu kann beispielsweise in einem Steuergerät der Prozessor bzw. μ-The control of the switch S can be implemented, for example, by a computer circuit. For this purpose, the processor or μ-
Controller verwendet werden. In Abhängigkeit von Funktionen ist es dabei möglich, dass die Grenzfrequenz verändert wird, indem die Pulsweite entsprechend eine Veränderung erfährt. Soll der Tiefpassfilter beispielsweise zur Tiefpassfϊlterung von Beschleunigungssignalen verwendet werden, kann je nach Signalanalyse die Grenzfrequenz erhöht oder erniedrigt werden, um bessere Aussagen über das Signal zu erhalten. Es ist jedoch auch möglich, eine feste Pulsweitenmodulation einzustellen, die durch eine festverdrahtete elektronische Schaltung realisiert ist. Controller can be used. Depending on the functions, it is possible that the cutoff frequency is changed by the pulse width experiencing a change accordingly. If the low-pass filter is to be used, for example, for low-pass filtering acceleration signals, the cut-off frequency can be increased or decreased depending on the signal analysis in order to obtain better information about the signal. However, it is also possible to set a fixed pulse width modulation, which is implemented by a hard-wired electronic circuit.

Claims

Ansprüche Expectations
1. Tiefpasschaltung, die eine veränderbare Grenzfrequenz aufweist, dadurch gekennzeichnet, dass die Tiefpassschaltung derart konfiguriert ist, dass die Tiefpassschaltung mittels einer Pulsweitenmodulation die Grenzfrequenz verändert.1. Low-pass circuit which has a variable cut-off frequency, characterized in that the low-pass circuit is configured such that the low-pass circuit changes the cut-off frequency by means of pulse width modulation.
2. Tiefpassschaltung nach Anspruch 1, dadurch gekennzeichnet, dass die Pulsweitenmodulation ein Schalter S vorgesehen ist. 2. Low pass circuit according to claim 1, characterized in that the pulse width modulation a switch S is provided.
PCT/DE2004/002536 2004-01-27 2004-11-18 Low-pass circuit WO2005071836A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102004003971.2 2004-01-27
DE200410003971 DE102004003971A1 (en) 2004-01-27 2004-01-27 Low-pass circuit

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3536731A1 (en) * 1985-10-15 1987-04-23 Siemens Ag Controllable low-pass filter

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3536731A1 (en) * 1985-10-15 1987-04-23 Siemens Ag Controllable low-pass filter

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