DEVICE FOR DIGITIZING AN ANALOGUE SIGNAL

Abstract

A device for digitizing an analogue signal, wherein a distortion signal outlet of a distortion signal generator is only coupled to an analogue digital converter by passive components.

Claims

1. An apparatus for digitizing an analog signal, comprising: an analog-to-digital converter having a signal input for the analog signal, and a distortion signal generator having a distortion signal output, wherein the distortion signal generator is designed to deliver a distortion signal at the distortion signal output, wherein the distortion signal output is coupled to the analog-to-digital converter exclusively by passive components.

2. The apparatus as claimed in claim 1, wherein the distortion signal output is coupled to the analog-to-digital converter without active components.

3. The apparatus as claimed in claim 1, wherein the analog-to-digital converter is part of a microcontroller.

4. The apparatus as claimed in claim 3, wherein the distortion signal generator is also part of the microcontroller.

5. The apparatus as claimed in claim 4, wherein the distortion signal generator is implemented by a digital output of the microcontroller, which forms the distortion signal output.

6. The apparatus as claimed in claim 1 wherein, the analog-to-digital converter has a differential input, and wherein the distortion signal output is coupled to a connection of the differential input.

7. The apparatus as claimed in claim 6, wherein the distortion signal output and a reference potential have a voltage divider connected between them, and wherein the connection of the differential input is connected to an output of the voltage divider.

8. The apparatus as claimed in claim 7, wherein the connection of the differential input and the reference potential have a capacitor (C1) connected between them, which spans at least one resistor of the voltage divider.

9. The apparatus as claimed in claim 1, wherein the analog-to-digital converter has a reference input in addition to the signal input, and wherein the distortion signal output is coupled to the reference input.

10. The apparatus as claimed in claim 9, wherein the distortion signal output and a reference potential have a voltage divider connected between them, and wherein the reference input is connected to an output of the voltage divider.

11. The apparatus as claimed in claim 10, wherein the reference input and the reference potential have a capacitor connected between them, which spans at least one resistor of the voltage divider.

12. The apparatus as claimed in claim 1, wherein the distortion signal output and a signal connection delivering the signal are coupled to the signal input.

13. The apparatus as claimed in claim 12, wherein the distortion signal output is coupled by DC voltage to the signal input, and the signal connection is coupled by AC voltage to the signal input.

14. The apparatus as claimed in claim 12, wherein the distortion signal output and a reference potential have a voltage divider connected between them, and wherein the signal input is connected to an output of the voltage divider.

15. The apparatus as claimed in claim 7, wherein a resistor of the voltage divider that is connected between the distortion signal output and the output of the voltage divider is larger than a second resistor that is connected between the output of the voltage divider and the reference potential.

16. The apparatus as claimed in claim 1, wherein the distortion signal output is coupled to the analog-to-digital converter without an operational amplifier.

17. The apparatus as claimed in claim 2, wherein the analog-to-digital converter is part of a microcontroller.

18. The apparatus as claimed in claim 7, wherein the reference potential is ground.

19. The apparatus as claimed in claim 10, wherein the reference potential is a positive potential (New) The apparatus as claimed in claim 13, wherein the distortion signal output and a reference potential have a voltage divider connected between them, and wherein the signal input is connected to an output of the voltage divider.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Further features and advantages will be deemed by a person skilled in the art from the exemplary embodiment described below with reference to the appended drawing, in which:

[0028] FIG. 1: shows a microcontroller having circuitry according to a first exemplary embodiment,

[0029] FIG. 2: shows a microcontroller having circuitry according to a second exemplary embodiment, and

[0030] FIG. 3: shows a microcontroller having circuitry according to a third exemplary embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] FIG. 1 shows a microcontroller μC that has an integrated analog-to-digital converter ADC. The latter has a differential input, wherein the differential input has a positive connection ADC+ and a negative connection ADC−. A voltage difference applied between the two connections ADC+, ADC− is digitized by the analog-to-digital converter ADC.

[0032] The microcontroller μC has a digital output D, which is used in the present case as a distortion signal output. The microcontroller μC is therefore also used as a distortion signal generator at the same time. The microcontroller has software implemented in it that ensures that the digital output D can be actuated in pulse width modulated fashion or with a square wave signal, for example in a manner as already described further above, so that the circuit described below is used to produce a defined distortion signal. A frequency of a square wave signal or of another signal can be determined particularly by means of software in this case.

[0033] The digital output D is connected to ground via a voltage divider S, wherein the voltage divider S has a first resistor R1 and a second resistor R2. The first resistor R1 has a much higher resistance value in this case than the second resistor R2. Hence, the signal delivered by the digital output D, which can alternate between ground and a supply voltage for the microcontroller μC, is divided down to a substantially smaller value that, in the present case, corresponds in terms of voltage to three least significant bits (LSB) of the analog-to-digital converter ADC. The second resistor R2 moreover has a capacitor C1 interconnected across it that can be charged by the voltage divider S. The capacitor C1 is in this case connected to an output of the voltage divider S that is situated between the two resistors R1, R2. When the digital output D assumes a positive potential, the capacitor C1 is charged in this manner. When the digital output D assumes a negative potential, the capacitor C1 is discharged. This allows accurate setting of the voltage of the capacitor C1. By way of example, the distortion signal can be produced as a sequence of different pulse width modulation settings at the digital output D. However, it is also possible for intermediate values to be produced at the output of the voltage divider S using the capacitor C1, particularly between the values that the output of the voltage divider S assumes at a high and a low potential at the distortion signal output. In this case, measurements are thus taken particularly while the voltage at the output of the voltage divider S rises and falls, the design of the components preferably being proportioned such that the voltage rises and falls uniformly.

[0034] The output of the voltage divider S and that connection of the capacitor C1 that is connected thereto are furthermore connected to the negative connection ADC− of the analog-to-digital converter ADC. Hence, the signal applied to the positive connection ADC+ is digitized relative to a voltage value that is adjustable by means of the digital output D. This allows superimposition of a distortion signal adjustable by the digital output D in a similar manner to how this would take place in the event of superimposition of the distortion signal by means of an upstream adder, as customary in the prior art. Use of the active components necessary for this purpose according to the prior art can be dispensed with, however.

[0035] The positive connection ADC+ has a signal VS applied to it that is intended to be digitized. In the present case, the microcontroller μC further has a reference connection Ref that is connected to a reference voltage VR. The latter is used internally in the microcontroller μC, but is of no further relevance to the interconnection shown in FIG. 1.

[0036] The microcontroller μC is furthermore designed to produce a defined signal train, in the present case in the form of a sawtooth signal, at the negative connection ADC−. To this end, the digital output D is actuated as appropriate, so that the capacitor C1 assumes the necessary voltages. Since the microcontroller μC produces these values itself, it knows them too and is able to evaluate the signals delivered by the analog-to-digital converter ADC as appropriate. In particular, a multiplicity of measurements carried out successively are used to form a mean value, this mean value being more accurate than the resolution of the analog-to-digital converter ADC. The possible sampling frequency of the analog-to-digital converter ADC is substantially higher than would be required for sampling the signal VS, however. The mean value formation just described using the distortion signal can consequently convert the higher, but not immediately needed, temporal resolution into a better sampling resolution. This affords advantages for numerous applications, since it is possible to dispense with the use of a higher-quality, possibly external analog-to-digital converter.

[0037] It should be mentioned that the use of a sawtooth signal as distortion signal is advantageous in many applications. Said signal can be produced at the digital output D by means of a sequence of pulse width modulation signals, for example. However, a good approximation of a triangular function is also possible, particularly from sections of an exponential function during charging and discharge of the capacitor C1. This is based particularly on the insight that the rise in the voltage across the capacitor C1 is the same for charging and discharge.

[0038] FIG. 2 shows a microcontroller having circuitry according to a second exemplary embodiment.

[0039] It should be understood that the fundamental operation of the use of a distortion signal is embodied similarly to the first exemplary embodiment. Therefore, only the differences in the second exemplary embodiment in relation to the first exemplary embodiment are discussed below.

[0040] In contrast to the analog-to-digital converter ADC of the first exemplary embodiment, the analog-to-digital converter ADC of the second exemplary embodiment has no differential input. It has merely a positive connection ADC+ to which the signal VS to be digitized is connected. Measurements are taken relatively to a purely internal negative connection ADC− that is hardwired to ground and unalterable.

[0041] The microcontroller μC has a digital output D in the same way as in the first exemplary embodiment. Said output is likewise coupled to a voltage divider S having two resistors R1, R2, with a capacitor C1 being interconnected across the second resistor R2. In contrast to the first exemplary embodiment, however, the voltage divider S has its end opposite the digital connection D connected not to ground but rather to a supply voltage VDD. In principle, this allows a distortion signal to be produced in a very similar manner to that described with reference to the first exemplary embodiment.

[0042] As a further difference, the output of the voltage divider S, to which the capacitor C1 is also connected, is connected not to the negative connection ADC− but rather to the reference connection. This reference connection is an input for a reference potential that is used in the analog-to-digital converter ADC and that divides the signal applied to the positive connection ADC+ before it is digitized. In the present case, the superimposition is thus effected not by means of a summation or subtraction, but rather by means of a division. In the case of the second exemplary embodiment, the microcontroller μC is programmed such that it likewise forms mean values, but taking into consideration the differently superimposed distortion signal. This allows a conversion from temporal resolution into a better sampling resolution to be performed in the same way.

[0043] FIG. 3 shows a microcontroller μC having circuitry according to a third exemplary embodiment. In this case, in contrast to the first and second exemplary embodiments, the distortion signal is not coupled directly to the microcontroller μC, but rather the distortion signal is superimposed on the signal VS to be digitized instead. In this case, the signal VS to be digitized is coupled by means of a capacitor C1, so that it is coupled by AC voltage. A DC voltage component of the signal VS is therefore masked out. The digital output D of the microcontroller μC is connected to a voltage divider S in the same way as in FIG. 1, said voltage divider having two resistors R1, R2 and having its end opposite the digital output D connected to ground. The output of the voltage divider S, which is situated between the resistors R1, R2, is connected to the capacitor C1. The same connection is also connected to the positive connection ADC+. Moreover, it is connected to a third resistor R3, which has its opposite connection in turn connected to a supply voltage VDD. The reference input Ref of the microcontroller μC is firmly connected to a reference potential VR in the present case.

[0044] The circuitry described and shown in FIG. 3 superimposes the distortion signal, the absolute value of which is matched by means of the voltage divider S as already described further above, directly on the signal VS to be digitized before the latter is coupled into the analog-to-digital converter ADC. Although the circuitry shown in FIG. 3 has a somewhat different transfer characteristic than an adder embodied with active components such as operational amplifiers, for example, this transfer characteristic is sufficient for typical applications. In particular, it can be compensated for in the computations performed by the microcontroller μC. Dispensing with active components achieves a marked decrease in complexity and costs.

[0045] The claims that are part of the application do not constitute dispensing with attaining further protection.

[0046] If, in the course of the procedure, it is found that a feature or a group of features is not absolutely necessary, then the applicant is right now seeking a wording for at least one independent claim that no longer has the feature or the group of features. This may be, by way of example, a subcombination of a claim available on the filing date or a subcombination of a claim available on the filing date restricted by further features. Such claims or combinations of features to be reworded are intended to be understood as also covered by the disclosure of this application.

[0047] It should further be pointed out that configurations, features and variants of the invention that are described in the different embodiments or exemplary embodiments and/or are shown in figures are combinable with one another arbitrarily. Single or multiple features are interchangeable with one another arbitrarily. Combinations of features that result from this are intended to be understood as also covered by the disclosure of this application.

[0048] Back-references in dependent claims are not intended to be understood as dispensing with attaining independent, substantive protection for the features of the back-referenced subclaims. These features can also be combined with other features arbitrarily. Features that are merely disclosed in the description or features that are disclosed in the description or in a claim only in conjunction with other features may fundamentally be of separate significance essential to the invention. They can therefore also be included individually in claims to distinguish from the prior art.