Method for operating a filter device, method for filtering, differential filter device which can be calibrated, computer program, and computer-readable medium

Abstract

The present invention relates to a method for operating a differential filter device (1) which can be calibrated and which comprises: a first branch (2), in particular provided for a main signal; a second branch (3), in particular provided for a complementary signal which is inverted in comparison with a main signal; first calibration means (4) for setting at least one filter frequency of the first branch (2); and second calibration means (5) for setting at least one filter frequency of the second branch (3); in which method at least one filter frequency of the first branch (2) is set using the first calibration means (4) and / or at least one filter frequency of the second branch (3) is set using the second calibration means (5), the at least one filter frequency of the first branch (2) being different from the at least one filter frequency of the second branch (3).

Description

[0001] DESCRIPTION

[0002] Method for operating a filter device, method for filtering, calibratable differential filter device, computer program and computer-readable medium

[0003] The invention relates to a method for operating a calibratable differential filter device, which has a first branch, provided in particular for a fundamental signal, and a second branch, provided in particular for a complementary signal that is inverted compared to a fundamental signal, and first calibration means for setting at least one filter frequency of the first branch and second calibration means for setting at least one filter frequency of the second branch, in which at least one filter frequency of the first branch is set with the first calibration means and / or at least one filter frequency of the second branch is set with the second calibration means. Furthermore, the invention relates to a calibratable differential filter device, a method for filtering, a computer program, and a computer-readable medium.

[0004] In general, a distinction is made between single-ended signaling and differential signaling, which is also called symmetrical signaling.

[0005] In asymmetric signal transmission, a variable voltage representing a signal is typically routed over a single line. A ground, for example, serves as a reference. If multiple signals are to be transmitted, a common reference line can be used, so the total number of lines required can be equal to the number of signals plus the common reference line.

[0006] In the differential scenario, however, a signal is transmitted using two complementary electrical signals propagating through two separate lines. Specifically, one line carries a fundamental signal, and the second carries an inverted signal, which can also be referred to as a complementary signal. The complementary signal is ideally of equal magnitude but is characterized by a polarity opposite to that of the fundamental signal. In differential signal transmission, the (respective) complementary signal typically serves as the reference for the (respective) fundamental signal, rather than ground as the overarching reference.

[0007] The differential scenario therefore requires more lines, but offers the significant advantage of being less susceptible to noise picked up during signal transmission. This is because any noise picked up by the fundamental signal and the complementary signal can be canceled out when the fundamental and complementary signals are summed or subtracted.

[0008] It may be desired or necessary to filter signals. Filter devices can be used for this purpose. In this case, filtering is understood to mean filtering with respect to frequency, in particular the filtering out of at least one frequency or frequency component from a given signal. Examples of corresponding devices include low-pass or high-pass filters. A low-pass filter is a filter that allows signal components with a frequency below an upper cut-off frequency, also referred to as the filter frequency, to pass through, while attenuating those with higher frequencies. With a high-pass filter, the behavior is exactly the opposite with respect to a lower cut-off frequency, also referred to as the filter frequency. A band-pass filter is a filter that allows a specific frequency band to pass through, but attenuates frequency ranges above and below it. In other words, a band-pass filter has two filter or cut-off frequencies: an upper and a lower.

[0009] Differential filter devices can be used to filter differentially transmitted signals. These devices have two lines, also referred to as branches. The fundamental signal can propagate through one branch, and the complementary signal through the other.

[0010] Calibratable differential filter devices exist that allow adjustment of the filter frequency(ies). This can be used, for example, to subsequently compensate for component-related deviations when an application requires a particularly precise (upper and / or lower) filter frequency. A calibratable, or in other words, adjustable, filter frequency can be implemented in a conventional manner using one or more adjustable elements of a filter device. These can be one or more elements whose capacitance (C), resistance (R), or inductance (L) is adjustable.

[0011] To increase the resolution of a calibratable differential filter device, additional elements must typically be installed. For example, doubling the resolution would, in the worst case, require twice the number of calibratable elements. Increasing the resolution therefore entails considerable design effort and high costs.

[0012] It is an object of the present invention to provide a method of the type mentioned at the outset which enables an extended resolution with comparatively low structural effort of the filter device.

[0013] The object is achieved in a method of the type mentioned at the outset in that the at least one filter frequency of the first branch differs from the at least one filter frequency of the second branch.

[0014] The invention further relates to a calibratable differential filter device which has a first branch provided in particular for a fundamental signal and a second branch provided in particular for a complementary signal inverted compared to a fundamental signal and first calibration means for setting at least one filter frequency of the first branch and second calibration means for setting at least one filter frequency of the second branch, wherein the filter device comprises means which are adapted to carry out the steps of the method according to the invention.

[0015] In other words, the present invention is based on the finding that with a calibratable differential filter device of a given design, an increased resolution can be achieved if the two branches are not switched the same, but deliberately differently. The setting of the calibration means is selected according to the invention such that the filter frequency of one branch differs from that of the other branch. The resulting filter frequency of the device, which is obtained after summation or difference formation, then lies between the two different values ​​of the two branches, in particular approximately midway between them. By moving away from only symmetrical settings and deliberately using asymmetrical settings of the two branches, it becomes possible to obtain additional filter frequency values ​​that lie between values ​​to which the two branches can actually be calibrated.In other words, the invention makes an extended resolution possible, whereby resolution is understood in particular to mean the accuracy with which the filter frequency of the filter device can be adjusted.

[0016] Purely by way of example, it should be mentioned that a filter frequency of 24 MHz is set for the first branch by means of the first calibration means and a filter frequency of 25 MHz is set for the second branch by means of the second calibration means, so that an intermediate value of approximately 24.5 MHz is obtained.

[0017] The fact that the filter device is calibratable means that at least one, in particular an upper and / or a lower, filter frequency can be adjusted. Calibration means are provided for this purpose.

[0018] The fact that the filter device is differential means that it can be used for filtering differential signals. For this purpose, it has two branches, one of which can be used for a fundamental signal and the other for an inverted complementary signal. It should be emphasized that it is irrelevant which branch is used for a fundamental signal and which branch for a complementary signal. The branches are expediently structurally identical, preferably comprising identical components, elements, and lines. The two branches are preferably part of a feedback path.

[0019] The means of the filter device according to the invention, which are adapted to carry out the steps of the method according to the invention, can be provided, for example, by suitable software, suitable hardware, or even a combination of suitable software and hardware. The filter device can comprise a decoder having one input and two outputs, in particular exactly one input and exactly two outputs.

[0020] One output of the decoder is preferably assigned to the first calibration means, and the other output is preferably assigned to the second calibration means, and in particular is connected to them. A connection is expediently such that the first and second calibration means can be addressed or controlled via an output signal from one or the other output of the decoder. In other words, the calibration means of one branch can then be controlled or adjusted via one output of the decoder, and those of the other branch via the other output. In particular, a signal for setting a desired filter frequency of the filter device can be received via the decoder input.

[0021] It is particularly preferred that the decoder has one input of n bits and two outputs of n-1 bits each.

[0022] A decoder can be implemented solely in hardware. The decoder can, in particular, be a component of the means of the filter device according to the invention that are adapted to carry out the steps of the method according to the invention, or it can form these means.

[0023] The inventive asymmetrical setting of the two branches makes additional filter frequency values ​​possible with a constant number of elements, e.g. basic and / or unit capacitances - specifically values ​​that lie between those that can be selected or set for each branch. A decoder with one input and two outputs, in particular one with one input with n bits and two outputs with n-1 bits each, makes it possible to select a higher number of filter frequency values ​​- e.g. corresponding to 4 bits - which is "translated" into setting or controlling a comparatively smaller number of filter frequency values ​​for the individual paths. Purely as an example, 4 bits go into the decoder, but only 3 bits are controlled per branch. The feedback branches are then correspondingly smaller and simpler.

[0024] The decoder is expediently designed and / or configured such that, in particular in response to the receipt of an input signal, it can output an output signal via both outputs, wherein the output signals of the two outputs differ from one another. This is done in order to be able to set or to set the first and second calibration means differently.

[0025] In particular, it can additionally be designed and / or configured such that, in response to the receipt of an input signal, it can output or outputs two matching output signals via the two outputs. This is particularly important in order to be able to adjust the first and second calibration means simultaneously.

[0026] The decoder can in particular be designed and / or configured in such a way that it can output or does output two different output signals via the two outputs for some input signals and can output or does output two matching output signals via the two outputs for other, different input signals.

[0027] It should be noted that while binary decoding will generally be expedient, alternatives are by no means excluded, with thermal codes being mentioned as an example. As a rule, the first calibration means are designed and / or configured to be able to set the at least one filter frequency of the first branch to discrete filter frequency values, and the second calibration means are designed and / or configured to be able to set the at least one filter frequency of the second branch to discrete filter frequency values. The discretely adjustable values ​​of the two branches preferably coincide.Then, it is further preferred that the at least one filter frequency of the first branch is set to a discrete filter frequency value or a corresponding setting is left unchanged, and the at least one filter frequency of the second branch is set to the next higher or next lower discrete filter frequency value. In other words, one branch can be set to one calibration level or the setting of such a level can be left unchanged, and the other branch is set to the next higher or next lower calibration level. If a decoder is provided, it can be designed and / or configured accordingly.

[0028] It is also possible for a value for a filter frequency to which the filter device is to be calibrated to be received. The desired value can be received, for example, from a user who is adjusting the filter device. It is also possible for the filter device to receive a desired value, in which case it is designed and / or configured accordingly. For example, software can be provided to which a value can be transferred or into which a value can be input, and / or a decoder.

[0029] If a value is received, in an advantageous further development the filter frequency of the first branch is preferably automatically set to a value different from the received value by means of the first calibration means and / or the filter frequency of the second branch is preferably automatically set to a value different from the received value by means of the second calibration means.

[0030] The filter frequency of the first branch can then, for example, be set to a value above the received value, and the filter frequency of the second branch to a value below the received value. The reverse is also possible.

[0031] Purely by way of example, it should be mentioned that a desired filter frequency of (approximately) 24.5 MHz is received or entered and a particularly automatic setting of the filter frequency of the first branch to 24 MHz and of the second branch to 25 MHz takes place.

[0032] An automatic setting or adjustment can, for example, also be implemented in software and / or with the help of a decoder that is implemented purely in hardware.

[0033] A further embodiment is characterized in that the at least one filter frequency of the second branch is or is set at least by a factor of 1.03 higher than the at least one filter frequency of the first branch, or vice versa. In other words, the filter frequency of one branch is then at least 3% higher than that of the other. If the filter frequency of the first branch is set to 24 MHz, for example, a filter frequency of 24 MHz * 1.03 = 24.72 MHz or more would be selected for the second branch. In particular, it can be provided that the at least one filter frequency of the second branch is or is set by a factor in the range from 1.03 to 1.10 higher than the at least one filter frequency of the first branch, or vice versa. In an expedient embodiment, the calibration means for calibrating the at least one filter frequency of the first and second branch comprise (each) one or more adjustable elements.The adjustable element(s) are in particular adjustable in terms of capacitance (C), resistance (R) or inductance.

[0034] Thus, it can be provided that the first calibration means comprise at least one adjustable capacitance and / or that the second calibration means comprise at least one adjustable capacitance. Then, preferably, at least one of the adjustable capacitances is adjusted such that different capacitance values ​​are obtained for the two branches.

[0035] The or at least one adjustable capacitance can also comprise a binary-weighted capacitor arrangement or be provided by such a capacitor arrangement. It is then further preferred that the (respective) binary-weighted capacitor arrangement comprises a plurality of capacitors, each of which can be switched on or off to obtain a desired capacitance value of the capacitor arrangement. It has then proven particularly suitable if one of the capacitors of the capacitor arrangement represents or forms a base capacitance and the further capacitor(s) are each provided by a unit capacitance, wherein the (respective) unit capacitance is characterized by a lower capacitance value than the base capacitance and / or all unit capacitances have the same capacitance value.

[0036] If a decoder is provided which has an input with n bits and two outputs with n-1 bits each - one each for the first and the second calibration means -, in a preferred development, the number of capacitors in the capacitor arrangement of the first and / or the second calibration means 2 n 1 Purely as an example, the decoder has 3-bit outputs, in other words, 3 bits can be controlled with each output. The 3 bits would be assigned a number of 2 3 = 8 capacitors, e.g. one basic capacitance and seven unit capacitances.

[0037] Alternatively or additionally, it can be provided that the first calibration means comprise at least one adjustable resistor and / or that the second calibration means comprise at least one adjustable resistor. If this is the case, at least one of the adjustable resistors can be adjusted such that different resistance values ​​are obtained for the two branches. With regard to adjustable resistors - analogous to capacitors - it applies that these comprise a binary-weighted resistor arrangement or can be provided by such a resistor arrangement. Then it is further preferred that the (respective) binary-weighted resistor arrangement has a plurality of capacitors, each of which can be switched on or off in order to obtain a desired resistance value of the resistor arrangement.

[0038] Even in the case of a resistor arrangement, it can be the case that one of the resistors in the resistor arrangement represents or forms a basic resistor and the further resistor(s) are (each) given by a unit resistor, whereby the (respective) unit resistor is characterized by a lower resistance value than the basic resistor and / or all unit resistors have the same resistance value.

[0039] Furthermore, if a decoder is provided with an input with n bits and two outputs with n-1 bits each - one each for the first and the second calibration means - it can apply in a preferred development that the number of resistors of the resistor arrangement of the first and / or the second calibration means 2 n 1 corresponds.

[0040] It can also be provided that the first calibration means comprise at least one adjustable inductive element and / or the second calibration means comprise at least one adjustable inductive element. Then, it is further preferred that at least one of the adjustable inductive elements is adjusted such that different inductance values ​​are obtained for the two branches.

[0041] In other words, to obtain different filter frequencies of the two branches, different capacitances and / or different resistances and / or different inductances can be set for them.

[0042] In a further development, the filter device can comprise at least one operational amplifier. In this case, a first input of the operational amplifier is preferably assigned to the first branch and a second input of the operational amplifier is assigned to the second branch. In particular, a first input of the operational amplifier is on the first branch and a second input is on the second. A signal propagating through the first branch, e.g. a fundamental signal, is then fed to the first input and a signal propagating on the second branch, e.g. a complementary signal, is fed to the second input. With appropriate circuitry, the operational amplifier can form a sum or difference of two signals propagating on the two branches.

[0043] In an advantageous development, it is then provided that the first calibration means or parts thereof are connected in parallel with the operational amplifier, and / or that the second calibration means or parts thereof are connected in parallel with the operational amplifier. Preferably, the calibration means of each branch or parts thereof are connected in parallel with each input of the operational amplifier.

[0044] It has proven particularly suitable if an adjustable capacitance of the first calibration means is connected in parallel to the operational amplifier, and an adjustable capacitance of the second calibration means is connected in parallel to the operational amplifier.

[0045] Furthermore, it can be provided that at least one resistor is connected in parallel to the first calibration means and / or that at least one resistor is connected in parallel to the second calibration means.

[0046] The filter device can further be designed as a low-pass or high-pass filter or at least comprise one such.

[0047] The filter device can also be designed as a Bessel filter, in particular as a preferably multi-pole Bessel low-pass filter, or at least comprise one such filter, which has proven particularly suitable. A five-pole Bessel low-pass filter is mentioned purely as an example. Other filter types are also possible, for example Chebyshev filters or Butterworth filters, which the filter device can also be designed as or at least comprise.

[0048] It can also be provided that the filter device is designed as a microchip or comprises such a microchip.

[0049] The invention further relates to a method for filtering, in which - a calibratable differential filter device is provided, which has a first branch provided in particular for a fundamental signal and a second branch provided in particular for a complementary signal inverted compared to a fundamental signal and first calibration means for setting at least one filter frequency of the first branch and second calibration means for setting at least one filter frequency of the second branch,

[0050] - the filter device is operated by carrying out the method according to the invention for operating a calibratable differential filter device, and

[0051] - differentially transmitted signals are filtered with the filter device.

[0052] In other words, following the inventive setting of the different filter frequencies for the two branches, differential signals can be filtered by means of the filter device, whereby an extended resolution is available.

[0053] The signals that are filtered within the scope of the present invention are, in particular, analog signals. These may be signals used in positioning methods, e.g., by so-called indoor positioning systems (IPS). This is to be understood purely as an example and does not exclude other areas of application. Filtering can be followed, for example, by an analog-to-digital conversion using an ADC.

[0054] The invention further relates to a computer program comprising instructions that cause the filter device according to the invention to execute the method steps according to the invention. The filter device can comprise a memory on which the computer program is stored. It is also possible for the filter device according to the invention to have a processor.

[0055] Finally, the invention relates to a computer-readable medium on which the computer program according to the invention is stored. The computer-readable medium can be, for example, a USB or flash memory, or a CD-ROM or DVD.

[0056] With regard to the embodiments of the invention, reference is also made to the subclaims and to the following description of embodiments with reference to the accompanying drawings.

[0057] The drawing shows:

[0058] Figure 1 is a purely schematic representation of a first embodiment of a calibratable differential filter device according to the invention, and

[0059] Figure 2 is a purely schematic representation of a second embodiment of a calibratable differential filter device according to the invention.

[0060] Identical or similar elements or components are provided with the same reference numerals in the figures.

[0061] Figure 1 shows an embodiment of a calibratable differential filter device 1 according to the invention. The device 1 according to Figure 1 is designed as a differential standard filter as a low-pass filter, this being understood as an example. The differential filter device 1 comprises, in a manner known per se, a first branch 2, provided in particular for a fundamental signal, and a second branch 3, provided in particular for a complementary signal that is inverted compared to a fundamental signal. In other words, during operation of the device 1, differential signals can propagate through the two branches, e.g. a fundamental signal through the first branch 2 and a complementary signal of opposite polarity through the second branch 3 (or vice versa). The two branches 2, 3 are identical in all their elements.

[0062] Furthermore, there are first calibration means 4 for setting at least one filter frequency of the first branch 2 and second calibration means 5 for setting at least one filter frequency of the second branch 3. As noted above, the filter device according to Figure 1 is designed as a low-pass filter, so that an upper cutoff frequency can be set as the filter frequency.

[0063] In the embodiment described here, both the first calibration means 4 and the second calibration means 5 are each provided by an adjustable capacitance 4, 5. In the example shown here, the adjustable capacitances 4, 5 are each designed as binary-weighted capacitor arrangements with several individual capacitors, each of which can be switched on or off in order to obtain a desired capacitance value of the capacitor arrangement. Discrete capacitance values ​​can be set. Each individual capacitor can, for example, be provided by or represent a unit capacitance. It is also possible for one of the individual capacitors to represent or form a base capacitance and for the other individual capacitors to each represent a unit capacitance, which has proven to be particularly suitable.Purely by way of example, the base capacitance corresponds to a frequency of 20 MHz and each unit capacitance corresponds to 1 MHz, so that an increase of 1 MHz is possible by adding a unit capacitance. In the illustrated embodiment, each adjustable capacitance 4, 5 comprises eight individual capacitors, namely one individual base capacitance capacitor corresponding to 20 MHz and one individual unit capacitance capacitor corresponding to one MHz.

[0064] It should be noted that in the simplified, purely schematic Figure 1, the individual capacitors of the binary-weighted arrangement are not shown separately, but rather the arrangements are each represented by an overarching circuit symbol for an adjustable capacitance. By means of the respective binary-weighted capacitor arrangement, discrete filter frequency values ​​can be set for the respective branch 2, 3 by switching capacitors on or off. As noted above, the two branches 2, 3 of the filter device are constructed identically with all their elements and components, so that this also applies to the binary-weighted capacitor arrangements 4, 5. Accordingly, these can be set to the same discrete capacitance and thus resulting filter frequency values ​​(if necessary, subject to any manufacturing-related tolerances).By switching off individual capacitors of the binary weighted capacitor arrangements 4, 5, these can be controlled digitally in a manner known per se.

[0065] Furthermore, it should be noted that it is possible for the first and / or second calibration means 4, 5 to comprise, alternatively or in addition to at least one adjustable capacitance, at least one adjustable resistor and / or at least one adjustable inductive element. A binary-weighted arrangement with digital control is also possible here. An operational amplifier 6 is also present. This has two inputs 7, 8, one of which is assigned to the first branch 2 and one to the second branch 3. Specifically, the first, positive input 7 is clearly located on the first branch 2, and the second, negative input 8 is located on the second branch 3, so that a signal propagating on the first branch 2, e.g., a fundamental signal, is fed to the first input 7, and a signal propagating on the second branch 3, e.g., a complementary signal, is fed to the second input 8.The operational amplifier 6 serves here as an active element in contrast to the passive adjustable capacitors 4, 5. The operational amplifier 6 provides in particular the output-side inversion and acts as a driver.

[0066] As can be seen, the first and second calibration means 4, 5—here, the adjustable capacitances 4, 5—are connected in parallel with the operational amplifier 6. Both the first branch 2 and the second branch 3 each have a path 9, 10 parallel to the operational amplifier 6, on which the respective adjustable capacitance 4, 5 is located. The two paths 9, 10 each connect an input 7, 8 to an output 11, 12 of the operational amplifier 6 and form a feedback path or are part of one.

[0067] Both the first branch 2 and the second branch 3 further comprise a resistor 13, 14 connected in parallel with the respective adjustable capacitance 4, 5 of branch 2, 3. The resistors 13, 14 are located on further, here outer parallel paths 15, 16 of the respective branch 2, 3, which are also part of the feedback path. Finally, each branch 2, 3 contains a further resistor 17, 18, located on the input side of the respective branch 2, 3 before the branching of the outer parallel paths 15, 16 of branches 2, 3.

[0068] In order to enable an extended resolution for the filtering with the device 1 of Figure 1, it is operated according to the embodiment of the method according to the invention for operating a calibratable differential filter device described below.

[0069] The first calibration means 4 is used to set a filter frequency of the first branch 3, and the second calibration means 5 is used to set a filter frequency of the second branch 3, wherein, according to the invention, the filter frequency of the first branch 2 differs from the filter frequency of the second branch 3. The filter frequencies are set here by appropriately selecting capacitance values ​​of the adjustable capacitances 4, 5. As can be seen from Figure 1, in the example described here, a filter frequency of 24 MHz is set for the first branch 2 and a filter frequency of 25 MHz for the second branch 3. This is indicated schematically in Figure 1 by arrows shown above and below the paths 15, 16, which are provided with corresponding values.For this purpose, the adjustable capacitance 4 of the first branch 2, specifically the binary-weighted capacitor arrangement 4 forming it, is set to a (capacitance) calibration level corresponding to the filter frequency value of 24 MHz. This is achieved by appropriate digital control. The adjustable capacitance 5 is in particular set to the next higher (capacitance) calibration level, which here corresponds to 25 MHz, also by appropriate digital control. In other words, the adjustable capacitances 4, 5 are switched differently using small digital measures. Due to the different filter frequencies of 24 MHz for the first branch 2 and 25 MHz for the second branch 3, the filter frequency of the device 1, which results from summation and subtraction, is approximately 24.5 MHz, which is indicated in Figure 1 on the right-hand side of the output side of the operational amplifier 6 by a corresponding formula. As a result, the resolution can be expanded.

[0070] The filter device 1 of Figure 1 comprises means adapted to carry out the steps of the method described above. It is possible for the filter device 1 to comprise suitable software. The software can, for example, perform or effect the digital control of the adjustable capacitances. The filter device 1 of Figure 1 can also be implemented on a microchip comprising corresponding software.

[0071] It is also possible that a value for a filter frequency to which the filter device 1 is to be calibrated is received. The filter device 1 can be designed and / or configured for this purpose. If a value for a desired filter frequency is received, the filter frequency of the first branch 2 is preferably automatically set to a value different from the received value by means of the first calibration means 4 and / or the filter frequency of the second branch 3 is automatically set to a value different from the received value by means of the second calibration means 5. The filter frequency of the first branch 2 is then expediently set to a value above the received value and the filter frequency of the second branch 3 to a value below the received value. The reverse case is equally possible. This can also be implemented in software. E.g.a user can pass a desired value of 24.5 MHz to the software, whereby corresponding input means may be present, and the software digitally controls the adjustable capacitance 4 and the adjustable capacitance 5 accordingly or causes such control.

[0072] It is also possible for the filter device 1 to comprise a decoder (not shown in the figure) and possibly a bus. The decoder, which can be implemented purely in hardware, then expediently has an n-bit input, connected in particular to the bus, and two n-1-bit outputs, one of each of the two outputs being assigned to a branch 2, 3 or to the adjustable calibration means 4, 5 of each branch 2, 3. Purely by way of example, it should be mentioned that the decoder has a 4-bit input and two 3-bit outputs. Each output is assigned to a branch 2, 3 in order to be able to adjust its calibration means 4, 5.

[0073] The bus can then have in particular 16 bit inputs, so that 16 different values ​​for the filter frequency of the filter device 1 can be set.

[0074] In the following table - purely as an example - the left column shows 4-bit input values ​​from 0 to 14 for the decoder and the middle and right columns show the corresponding 3-bit output values ​​or codes output by the decoder for the two branches 2, 3. The 1st branch according to this table can, for example, be the upper branch 2 in Figure 1 and the 2nd branch according to the table the lower 3 or vice versa.

[0075] Purely as an example, an input of "0" means that for the adjustable capacitances 4 and 5 of both branches 2 and 3, only the base capacitance corresponding to 20 MHz is selected. This would correspond (after summing or subtracting) to the smallest adjustable filter frequency value of filter device 1 of 20 MHz.

[0076] With an input of "1", a unit capacitance corresponding to 1 MHz is added to one of the two branches 2, 3 - according to the table, the 2nd branch 3 - in addition to the basic capacitance, this is done by appropriate digital control of the adjustable capacitance 5. In other words, a frequency of 20 MHz remains set for the 1st branch 2, and 21 MHz is selected for the 2nd branch 3. The input value "1" thus corresponds (after summation or subtraction) to a filter frequency of device 1 of approximately 20.5 MHz. The setting "2" corresponds to outputs of "1" for both branches. In other words, one unit capacitance is added to each of the calibration devices 4 of the 1st branch 2 and the calibration devices 5 of the 2nd branch 3, so that a total of 21 MHz is obtained for both branches. An input value “3” with 21 MHz (basic capacity + 1 unit capacity) for the 1st.Branch 2 and 22 MHz (basic capacitance + 2 unit capacitances) for the 2nd branch 3 gives a total of 21.5 MHz, an input value “4” 22 MHz, “5” 22.5 MHz and so on.

[0077] As you can see, in the example shown, 4 bits are input, but only 3 bits are controlled per branch 2 and 3. The feedback branches can be correspondingly smaller or simpler.

[0078] As the table shows, the decoder is designed and / or configured such that it can output two different output signals via the two outputs for some input signals (1, 3, 5, 7, 9, ...), and can output two identical output signals via the two outputs for other, different input signals (0, 2, 4, 6, 8, ...). This allows the first 4 and the second calibration means 5 to be set differently or identically.

[0079] Following calibration of the filter frequency to a desired value, for example (approximately) 24.5 MHz by setting the different frequencies for the two branches 2, 3 (input value “9” and different output values ​​“4” and “5” for 24 MHz and 25 MHz in the table above), the filter device 1 can be used to filter differential signals. In this case, analog differential signals are filtered, specifically those used in position determination processes, e.g. by so-called indoor positioning systems (IPS). However, this is purely an example and other areas of application are by no means excluded. The filtering can be followed, for example, by analog-to-digital conversion using an ADC.

[0080] Figure 2 shows a second embodiment of a calibratable filter device 1 according to the invention. Unlike the device 1 according to Figure 1, this is designed as a differential multi-feedback filter with a low-pass filter. Since the filter device of Figure 2 largely corresponds to the filter device of Figure 1 and differs from it only in a few additional elements, only the additional elements are described below.

[0081] Specifically, the filter device 1 of Figure 2 has an additional resistor 19, 20 in each of the two branches 2, 3, here between the branching of paths 15 and 9, or 16 and 10, respectively. Furthermore, an additional adjustable capacitor 21 is present, which is located in a path 22 connecting the two branches 2, 3. These are typically common components of a multifeedback filter.

[0082] It should be noted that the arrangement according to Figure 2 can also represent, by way of example, one of several stages of a filter device 1 according to the invention.

[0083] The operation of the calibratable differential filter device 1 from Figure 2 can be carried out in the same way as the operation of the device from Figure 1 described above. In other words, different calibration levels can be selected in the same way for the adjustable capacitances 4 and 5 of the two branches 2 and 3 in order to obtain, for example, filter frequencies of 24 MHz and 25 MHz for the first and second branches 2, 3. Here, too, a bus and decoder and / or software can be used. Differential signals can then be filtered using the filter device from Figure 2. Multifeedback filters offer the advantage that they produce two poles with just one operational amplifier, meaning the frequency characteristic is significantly steeper.

[0084] List of reference symbols

[0085] 1 filter device

[0086] 2 first branch 3 second branch

[0087] 4 first calibration agent

[0088] 5 second calibration medium

[0089] 6 operational amplifiers

[0090] 7 first entrance 8 second entrance

[0091] 9 Path

[0092] 10 Path

[0093] 11 Exit

[0094] 12 Output 13 Resistance

[0095] 14 Resistance

[0096] 15 Parallel path

[0097] 16 Parallel path

Claims

CLAIMS 1. A method for operating a calibratable differential filter device (1) which has a first branch (2) provided in particular for a fundamental signal and a second branch (3) provided in particular for a complementary signal which is inverted compared to a fundamental signal, and first calibration means (4) for setting at least one filter frequency of the first branch (2) and second calibration means (5) for setting at least one filter frequency of the second branch (3), in which at least one filter frequency of the first branch (2) is set with the first calibration means (4) and / or at least one filter frequency of the second branch (3) is set with the second calibration means (5), characterized in that the at least one filter frequency of the first branch (2) differs from the at least one filter frequency of the second branch (3).

2. Method according to claim 1, characterized in that the first calibration means (4) are designed and / or configured to be able to set the at least one filter frequency of the first branch (2) to discrete filter frequency values, and in that the second calibration means (5) are designed and / or configured to be able to set the at least one filter frequency of the second branch (3) to in particular the same discrete filter frequency values, and the at least one filter frequency of the first branch (2) is set to a discrete filter frequency value or a corresponding setting is left and the at least one filter frequency of the second branch (3) is set to the next higher or next lower discrete filter frequency value.

3. Method according to claim 1 or 2, characterized in that a value for a filter frequency to which the filter device (1) is to be calibrated is received in particular from the filter device (1), and the filter frequency of the first branch (2) is preferably automatically set to a value different from the received value by means of the first calibration means (4), and / or the filter frequency of the second branch (3) is preferably automatically set to a value different from the received value by means of the second calibration means (5), preferably wherein the filter frequency of the first branch (2) is set to a value above the received value and the filter frequency of the second branch (3) is set to a value below the received value, or vice versa.

4. Method according to one of the preceding claims, characterized in that the first calibration means (4) comprise at least one adjustable capacitance and the second calibration means (5) comprise at least one adjustable capacitance, and at least one of the adjustable capacitances (4, 5) is adjusted such that different capacitance values ​​are obtained for the two branches (2, 3).

5. Method according to one of the preceding claims, characterized in that the first calibration means (4) comprise at least one adjustable resistor and the second calibration means (5) comprise at least one adjustable resistor, and at least one of the adjustable resistors is adjusted such that different resistance values ​​are obtained for the two branches (2, 3).

6. Method according to one of the preceding claims, characterized in that the first calibration means (4) comprise at least one adjustable inductive element and the second calibration means (5) comprise at least one adjustable inductive element, and at least one of the adjustable inductive elements is adjusted such that different inductance values ​​are obtained for the two branches (2, 3).

7. Method of filtering in which - a calibratable differential filter device (1) having a first branch (2) provided in particular for a fundamental signal and a second branch (3) provided in particular for a complementary signal inverted compared to a fundamental signal, and first calibration means (4) for setting at least one filter frequency of the first branch (2) and second calibration means (5) for setting at least one filter frequency of the second branch (3), - the filter device (1) is operated by carrying out the method according to one of claims 1 to 6, and - differentially transmitted signals are filtered with the filter device (1).

8. Calibrable differential filter device (1) comprising a first branch (2) provided in particular for a fundamental signal and a second branch (3) provided in particular for a complementary signal inverted compared to a fundamental signal, and first calibration means (4) for setting at least one filter frequency of the first branch (2) and second calibration means (5) for setting at least one filter frequency of the second branch (3), wherein the filter device (1) comprises means adapted to carry out the steps of the method according to one of claims 1 to 6.

9. Filter device (1) according to claim 8, characterized in that the first calibration means (4) are designed and / or arranged to be able to set the at least one filter frequency of the first branch (2) to discrete filter frequency values, and in that the second calibration means (5) are designed and / or arranged to be able to set the at least one filter frequency of the second branch (3) to the in particular same discrete filter frequency values.

10. Filter device (1) according to claim 8 or 9, characterized in that the first calibration means (4) comprise at least one adjustable capacitance, and / or that the second calibration means (5) comprise at least one adjustable capacitance.

11. Filter device (1) according to claim 10, characterized in that the or at least one adjustable capacitance (4, 5) comprises a binary weighted capacitor arrangement or is provided by such a capacitor arrangement, preferably, wherein the binary weighted capacitor arrangement has a plurality of capacitors which can each be switched on or off in order to obtain a desired capacitance value of the capacitor arrangement.

12. Filter device (1) according to one of claims 8 to 11, characterized in that the first calibration means (4) comprise at least one adjustable resistor, and / or that the second calibration means (5) comprise at least one adjustable resistor.

13. Filter device according to one of claims 8 to 12, characterized in that the first calibration means (4) comprise at least one adjustable inductive element, and / or that the second calibration means (5) comprise at least one adjustable inductive element.

14. Filter device (1) according to one of claims 8 to 13, characterized in that a decoder is provided which has an input, in particular of n bits, and two outputs, in particular of n-1 bits each, preferably, wherein one output is assigned to the first calibration means (4) and the other output is assigned to the second calibration means (5) and in particular is connected to these.

15. Filter device (1) according to claim 14, characterized in that the decoder is designed and / or arranged such that it can output an output signal via both outputs, in particular in response to the reception of an input signal, wherein the output signals of the two outputs differ from one another.

16. Filter device (1) according to one of claims 8 to 15, characterized in that the filter device (1) comprises at least one operational amplifier (6), preferably, wherein a first input (7) of the operational amplifier (6) is assigned to the first branch (2) and wherein a second input (8) of the operational amplifier (6) is assigned to the second branch (3).

17. Filter device (1) according to claim 16, characterized in that the first calibration means (4) or parts thereof are connected in parallel to the operational amplifier (6), and / or that the second calibration means (5) or parts thereof are connected in parallel to the operational amplifier (6).

18. Filter device (1) according to one of claims 8 to 17, characterized in that the filter device (1) is designed as a low-pass or high-pass filter or at least comprises such a filter.

19. Filter device (1) according to one of claims 8 to 18, characterized in that the filter device (1) is designed as a Bessel filter, in particular as a preferably multi-pole Bessel low-pass filter, or as a Chebyshev filter or as a Butterworth filter or at least comprises one such.

20. Computer program comprising instructions which cause the filter device (1) according to one of claims 8 to 19 to carry out the method steps according to one of claims 1 or 2.

21. A computer program comprising instructions which cause the filter device (1) according to claim 9 or one of claims 10 to 19, as far as they refer back to claim 9, to carry out the method steps according to claim 3, or which cause the filter device (1) according to claim 10 or claim 11 or one of claims 12 to 19, as far as they refer back to claim 10 or 11, to carry out the method steps according to claim 4, or which cause the filter device (1) according to claim 12 or one of claims 13 to 19, as far as they refer back to claim 12, to carry out the method steps according to claim 5, or which cause the filter device (1) according to claim 13 or one of claims 14 to 19, as far as they refer back to claim 13, to carry out the method steps according to claim 6.

22. A computer-readable medium on which the computer program according to claim 20 or 21 is stored.

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