DE102007001281A1 - Electronic measuring instrument for representation of signal processing, has trigger system and variable functions for connection of low frequencies and high frequencies - Google Patents

Abstract

The electronic measuring instrument for the representation of signal processing, has a trigger system and a variable function for connection of low frequencies and another variable function for connection of high frequencies during triggering. Both functions are generated using a single reversible digital filter that has a single digital low pass-filter.

Description

The The present invention relates to an electronic measuring device for representing the time course of signals, which is a trigger system includes. The meter has an adjustable function for the exclusion of low frequencies (LF reject) as well as an adjustable Function for the exclusion of high frequencies (HF-Reject) at the Triggering on. It particularly relates to an oscilloscope with these Functions.

Oscilloscopes typically provide triggering functions that limit the bandwidth of the trigger system input signal. Depending on the application, high or low frequencies are excluded from triggering. These trigger types are designated with LF-Reject or HF-Reject. The following functions are realized:
The low-frequency rejection trigger function excludes the low frequencies, ie a high-pass filter is placed in front of the trigger system, and the high frequency rejects the high-frequency rejection function locked out. Ie. In front of the trigger system, a low-pass filter is arranged. Consequently, both an adjustable high pass and an adjustable low pass are required before the trigger system.

In the case of digital trigger systems, the direct implementation of these filters involves a great deal of effort, so that very simple filters (IIR filters) are usually used here. In this regard, from the patent US 7,072,804 B2 a digital trigger filter for a real-time digital oscilloscope equipped with a digital trigger filter that performs LF-Reject and HF-Reject. The digital trigger filter includes first and second digitally implemented IIR filters. However, the use of special filters leads to greater restrictions in the filter function.

The Object of the present invention is therefore an improved Measuring device, in particular oscilloscope to provide, which high-pass or low-pass filtering for triggering realized in a particularly simple manner, without the filter function to significantly limit itself.

These Task is performed by an electronic measuring device according to the independent claim 1 solved. Advantageous developments are defined in the subclaims.

In A first embodiment of the invention is an electronic one Measuring device for displaying the time course of signals, which includes a trigger system, wherein the meter a adjustable function for the exclusion of low frequencies (LF reject) and an adjustable function to exclude high frequencies (RF reject) during triggering, characterized in that that both functions (LF Reject, HF Reject) using a realized single or single switchable digital filter become.

In In another embodiment, the switchable digital Filter further using a single or a few adjustable digital low-pass filters are realized.

The low frequency rejection (LF reject) function can be created by first subjecting an input signal to cyclic spectral shift by f _a / 2, then filtering with the single tunable digital low pass filter, and then again by cyclic spectral shift f _a / 2, where f _a / 2 is half the sampling rate or, according to the Nyquist theorem, the maximum frequency of the input signal. The cyclic spectral shift of the input signal can be realized by multiplying samples a _{k of} the input signal by the factor (-1) ^k , where a _{k is} the k th sample. This creates a high pass from the actual low pass.

In a further embodiment, the high-frequency rejection function (RF reject) may be generated by passing the input signal unchanged to the low-pass filter. In another embodiment, it can be generated by multiplying the sampled values a _{k of} the input signal by +1. Thus, the function of the low pass is not changed.

By the inventively established measuring device the effort to implement the filter function becomes significant reduced, without significant restriction of this feature even.

This and further aspects of the present invention will be described in the following detailed description with reference to the attached drawing described in detail in which

1 which represents the signal-theoretical basic principle of the method according to the invention on the basis of an exemplary signal curve;

2 schematically illustrates the structure of a meter for the joint implementation of the functions LF reject and RF reject using a single switchable digital filter; and

3 schematically illustrates the implementation of the single switchable digital filter using a single adjustable low-pass filter.

1 illustrates on the basis of an exemplary waveform the signal-theoretical principle of the invention, according to which a high-pass filter can be realized by means of a low-pass filter by mixing in the equivalent baseband position.

In other words, based on a Numerical Controlled Oscillator (NCO), a mixture of the sampled input signal into the complex baseband may be performed. For this, the following basic functions can be used u BB, real (t) = u HF (T) * cos (2.pi.f m t) u BB, imag (t) = u HF (T) * sin (2.pi.f m t) are used, where f _m corresponds to the mixing frequency of the numerical oscillator. In order to shift a sampled signal with the maximum frequency f = f _a / 2 into the equivalent low-pass range, the frequency f _m = f _a / 2 must be set for the mixing frequency of the NCO.

wobei k eine ganze Zahl ist. Folglich entfällt bei dieser besonderen Form der Mischung der Imaginärteil des Signals im äquivalenten Tiefpassbereich. Der Hochpass entsteht durch die Multiplikation mit der Folge [+1, –1, +1, –1, +1, ...], was einfach zu realisieren ist.Thus, the following expressions result for the output signals of the mixer:

where k is an integer. Consequently, in this particular form of mixing, the imaginary part of the signal in the equivalent low-pass range is eliminated. The high pass results from multiplication by the sequence [+1, -1, +1, -1, +1, ...], which is easy to realize.

It it becomes apparent that the actually desired high pass realized with a low pass in the equivalent low-pass range can be. After filtering, the signal must be the same Principle to be moved back into the high-frequency position.

2 schematically illustrates the structure of a measuring device 200 for the joint implementation of the functions LF-Reject and an RF reject using a single or single switchable digital filter 220 dar. The switchable filter 220 comprises an input for the sampled values a _{k of} the sampled signal 210 and an input for a selection signal 230 ,

By means of the selection signal 230 The switchable digital filter can be switched between the two functions LF-Reject and HF-Reject. The filtered signal is then turned into a trigger system 240 fed.

3 represents the structure of a switchable digital filter 300 for the joint implementation of a high pass and a low pass using a single low pass according to an embodiment of the present invention. The samples a _{k of} the sampled input signal 310 Depending on whether high frequencies (RF rejects) or low frequencies (LF rejects) are excluded during triggering, they are multiplied by +1 or by (-1) ^k , where k is an integer.

In the second case, the input signal is cyclically shifted by f _a / 2 by multiplying the sampling values a _k and thus transferred from the high-frequency range to the equivalent baseband (low-pass range). Since (-1) ^k = 1 for even k (2, 4, 6, ...), the shift can be realized by multiplying each odd-index sample by (-1). In one embodiment of the invention, the samples and the multiplication results may be represented in a one or two complement system such that multiplication by (-1) is limited to bitwise inverting the sample (and optionally adding 1). This achieves a particularly time-saving implementation of the function LF-Reject.

In In another embodiment of the invention, the function a lowpass can be generated by adding in both multipliers respectively the factor +1 is fed. This will cause the sampled input signal not changed. Thus, the trigger function HF Reject by selecting the factors +1 and setting the bandwidth of the Lowpasses are generated.

The Invention is not limited to the described embodiments limited. All described and / or drawn features are combined with each other in the invention as desired.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - US 7072804 B2 [0003]

Claims (7)

Electronic measuring device for displaying the time history of signals, which includes a trigger system, wherein the meter has a first adjustable function for the exclusion of low frequencies (LF reject) and a second adjustable function for the exclusion of high frequencies (RF reject) in the triggering characterized in that both functions (LF reject, RF reject) are generated using a single switchable digital filter. Electronic measuring device according to claim 1, characterized in that the only switchable digital filter includes a single digital low-pass filter. Electronic measuring device according to claim 1 or 2, characterized in that the function for the exclusion of low frequencies (LF reject) is generated in that an input signal first subjected to a cyclic spectral shift by f _a / 2, then with the single adjustable digital low-pass filter Filter is filtered and then again subjected to a cyclic spectral shift by f _a / 2, where f _a / 2 is half the frequency of the sampling rate f _a , with which the input signal is sampled digitally. Electronic measuring apparatus according to claim 3, characterized in that the cyclical spectral shift of the input signal is realized by multiplying samples a _{k of} the input signal by the factor (-1) ^k , where k is an integer and a _{k is} the k th sample. Electronic measuring device according to claim 2, characterized in that the function for excluding high Frequencies (RF reject) generated by this is the input signal is passed unchanged to the low-pass filter. Electronic measuring device according to one of claims 1 to 5, characterized in that the function for the exclusion of high frequencies (RF rejects) is generated by multiplying the sampling values a _{k of} the input signal by +1. Electronic measuring device according to one of the preceding claims, characterized in that the electronic meter is a digital oscilloscope.