Patent Description:
Measurement of broadband pulse signals, such as electromagnetic interference (EMI) measurement, requires a high dynamic range receiver due to a significant difference between a peak value of the pulse and a weighted indication of the detector within the resolution bandwidth. In other words, an achievable radio frequency (RF) bandwidth is limited by the dynamic range of the used components (e.g. <NUM> dB compression point of a mixer or amplifier, or signal-to-noise ratio (SNR) of an analog/digital converter).

This may be overcome by reducing a bandwidth at the critical components of the receiver with filters (preselection), the critical components including e.g. a first mixer of a heterodyne receiver or analog/digital converter at an intermediate frequency (IF) of a receiver or the baseband of a direct conversion receiver. Then, the measurement is done in a time-consuming sequential manner for every preselector filter path and measurement frequency. The prior art knows the document <CIT>, which pertains to the conversion of analog signals to digital format, particularly applicable for capturing wideband signals where the desired dynamic range of the system cannot be achieved by existing analog to digital converters. It is based on channelizing the input signal and frequency down-converting to allow each band to be sampled at a lower rate, digitizing, and then reconstructing the signal. Within a preselector filter bandwidth, the measurement may involve Fast Fourier Transform (FFT) methods to accelerate the measurement.

In view of the above, the present disclosure aims to improve a measurement of broadband pulse signals of the background art. An objective is to shorten a test time.

The objective is achieved by the embodiments as defined by the appended independent claims. Preferred embodiments are set forth in the dependent claims and in the following description and drawings.

An aspect of the present disclosure relates to a measurement system for a broadband signal. The system comprises a cross-over network, including an input port for the broadband signal; a plurality of output ports; and a plurality of frequency dividers, being configured to supply respective sub-bands of the broadband signal to the plurality of output ports. The plurality of frequency dividers comprises one or more of a low-pass filter and a high-pass filter. The system further comprises a processing unit, being configured to analyze the respective sub-bands of the broadband signal concurrently. It is very beneficial that a wide frequency range is split up into smaller sub-bands, wherein each sub-band is analyzed simultaneously (=concurrently). Thereby it is possible to analyze a wide frequency span of for example <NUM> to <NUM> at once. This not only accelerates the measurement but makes it possible to detect any irregular occurring peaks at all. For EMI measurement, the chances of missing a peak the DUT emits, is significantly reduced. In fact, DUTs like vehicles can be put into different test modes (for example acceleration from <NUM>/s to <NUM>/s on a test bench), wherein the spectrum the DUT emits is continuously monitored on a wide range. Any peak, even if it only occurs once (for example at <NUM>/s) can be detected with the measurement system according to the invention.

The processing unit may comprise a respective analog/digital converter, ADC, unit for the respective sub-band. This also comes along with the technical effect that all the sub-bands can be analyzed in parallel wherein each ADC only receives a certain bandwidth. Preferably, the RF signal of the respective sub-band is not mixed down before fed to the respective ADC. Instead the respective ADC is configured to digitize the RF signal of the assigned sub-band in the original frequency but with a reduced bandwidth of that sub-band.

The broadband signal may comprise a baseband signal.

Alternatively, the broadband signal may comprise an intermediate frequency, IF, signal.

The respective ADC unit for the respective sub-band may be configured to digitally sample the respective sub-band of the IF signal.

The respective ADC unit for the respective sub-band may be configured to digitally mix down the respective sub-band of the IF signal to the baseband.

The respective ADC unit for the respective sub-band may be configured to decimate a sampling rate of the respective sub-band of the IF signal. For example, the ADC can be operated at <NUM> with a resolution of <NUM> bit, but the decimation may result in a reduced data rate, such as e.g. <NUM>.

The processing unit may comprise a respective Fast Fourier Transform, FFT, unit for the respective sub-band. The respective FFT unit may be configured to perform a first plurality of concurrent FFT calculations in accordance with a second plurality of frequency bins being spread over the respective sub-band.

The respective frequency bin may be associated with at least <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM> FFT calculations per second.

The processing unit may comprise a respective detector unit for the respective sub-band; and the respective detector unit may be configured to perform a plurality of concurrent analyses of the respective sub-band in respect of one or more detection criteria.

The respective detector unit for the respective sub-band may comprise a number of detectors for the respective frequency bin.

The respective detector unit for the respective sub-band may comprise a plurality of concurrently operable detectors for the respective frequency bin. In that case, all the frequency bins obtained from all the sub-bands are analyzed in parallel by the detectors.

A first detector of the plurality of detectors of the respective frequency bin may be configured for peak detection; a second detector of the plurality of detectors of the respective frequency bin may be configured for quasi-peak detection; and a third detector of the plurality of detectors of the respective frequency bin may be configured for average detection. In that case, each frequency bin can be analyzed by a plurality of detectors at the same time.

The cross-over network may further comprise an amplifier arranged between subsequent frequency dividers of the plurality of frequency dividers.

The measurement system may further comprise a display unit. The processing unit may further be configured to display the respective analyzed sub-bands on the display unit.

According to the present disclosure, a broadband signal, such as a baseband signal or an IF signal of a heterodyne receiver, may be split into sub-bands, i.e., into a plurality of signals of limited bandwidth, which may be digitized and processed (e.g., digital down converted) concurrently.

The above-described aspects and implementations will now be explained with reference to the accompanying drawings, in which the same or similar reference numerals designate the same or similar elements.

The features of these aspects and implementations may be combined with each other unless specifically stated otherwise.

The drawings are to be regarded as being schematic representations, and elements illustrated in the drawings are not necessarily shown to scale. Rather, the various elements are represented such that their function and general purpose become apparent to those skilled in the art.

<FIG> illustrates a measurement system <NUM> in accordance with the present disclosure for a broadband signal.

The broadband signal to be analyzed may comprise a baseband signal, or an intermediate frequency, IF, signal, particularly of a heterodyne receiver. Especially for EMI measurements, a broad frequency range has to be measured. This in turn requires a high dynamic range of the receiver due to a significant difference between the peak values of the signal. In general, a pulse signal as well as a modulated signal have broad spectra.

The system <NUM> comprises a cross-over network <NUM>, including an input port <NUM> for the broadband signal, and a plurality of output ports <NUM>. As will be explained in more detail in connection with <FIG> below, the cross-over network <NUM> is configured to supply respective sub-bands of the broadband signal to the plurality of output ports <NUM>. In other words, the cross-over network 11is configured to preselect the respective sub-band of the broadband signal of a respective output port <NUM>.

The system <NUM> further comprises a processing unit <NUM>, being configured to analyze the respective sub-bands of the broadband signal concurrently. Concurrently means that the respective sub-bands of the broadband signal are analyzed at the same time by dedicated means.

To this end, the processing unit <NUM> may comprise a respective analog/digital converter, ADC, unit <NUM> for the respective sub-band.

The respective ADC unit <NUM> for the respective sub-band may be configured to digitally sample the respective sub-band of the IF signal. As such, the ADC units <NUM> are very fast (in compliance with the Shannon theorem) and operable on respective sub-bands of the original frequency band (for example <NUM> to <NUM>) of the broadband signal. The signal paths upstream the ADC units <NUM> are free of mixers.

Optionally, the respective ADC unit <NUM> for the respective sub-band may be configured to digitally mix down the respective sub-band of the IF signal to the baseband.

Optionally, the respective ADC unit <NUM> for the respective sub-band may be configured to decimate a sampling rate of the respective sub-band of the IF signal.

The processing unit <NUM> may further comprise a respective Fast Fourier Transform, FFT, unit <NUM> for the respective sub-band. The respective FFT unit <NUM> may be configured to perform a first plurality of concurrent FFT calculations in accordance with a second plurality of frequency bins being spread over the respective sub-band.

The respective FFT unit <NUM> may be arranged downstream of the respective ADC unit <NUM>. The respective FFT unit <NUM> may be configured to perform a <NUM>, <NUM> or <NUM>-point FFT, for example.

The respective frequency bin may represent <NUM> or <NUM> of bandwidth, for example, and may be associated with preferably more than <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or more than <NUM> FFT calculations per second. More preferably the respective frequency bin is associated with (at least) <NUM> FFT calculations per second.

The processing unit <NUM> may comprise a respective detector unit <NUM> for the respective sub-band.

The detector unit <NUM> may be arranged downstream of the respective FFT unit <NUM>. The respective detector unit <NUM> may be configured to perform a plurality of concurrent analyses of the respective sub-band in respect of one or more detection criteria, such as peak detection, quasi-peak detection and average detection.

In particular, the respective detector unit <NUM> for the respective sub-band may comprise a plurality of concurrently operable detectors for the respective frequency bin.

For example, a first detector of the plurality of detectors of the respective frequency bin may be configured for peak detection; a second detector of the plurality of detectors of the respective frequency bin may be configured for quasi-peak detection; and a third detector of the plurality of detectors of the respective frequency bin may be configured for average detection.

The measurement system <NUM> may further comprise a display unit <NUM>. The processing unit <NUM> may further be configured to display the respective analyzed sub-bands on the display unit <NUM>.

Assuming a bandwidth of <NUM> per frequency bin, the frequency band between <NUM> and <NUM> (according to CISPR standard) requires a quantity of (<NUM> - <NUM>) / <NUM> = <NUM> frequency bins. Each frequency bin may be associated with for example <NUM> FFT calculations per second, and an exemplary plurality of three concurrently operable detectors may be used for the respective frequency bin.

<FIG> illustrates a cross-over network <NUM> in accordance with the present disclosure of the measurement system <NUM> of <FIG>.

The cross-over network <NUM> already mentioned in connection with <FIG> includes a plurality of frequency dividers <NUM>, being configured to supply respective sub-bands of the broadband signal to the plurality of output ports <NUM>. As used herein, a frequency divider may refer to a frequency-selective filter.

The plurality of frequency dividers <NUM> comprises one or more of a low-pass filter and a high-pass filter as follows:
Starting from the input port <NUM>, a low-pass filter may be provided as a first frequency divider <NUM>. Preferably frequencies below <NUM> can pass without significant attenuation. As such, a frequency band of interest, such as <NUM> to <NUM> according to the CISPR standard, can be analyzed.

Then a first splitting stage may be provided downstream of the first frequency divider <NUM>. The first splitting stage may comprise a plurality of frequency-selective dividers <NUM> (in the embodiment there are two dividers, one of them being referenced as such). The first splitting stage may supply frequency bands of <NUM> to <NUM> and <NUM> to <NUM>.

A second splitting stage may be provided downstream the first splitting stage. The second splitting stage may comprise a plurality of frequency-selective dividers <NUM> (in the embodiment there are four dividers, one of them being referenced as such). The second splitting stage may further subdivide the frequency bands supplied by the first splitting stage. The second splitting stage may supply frequency bands of <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, and <NUM> to <NUM>, respectively.

The first and second splitting stages are configured in such a way that the input port <NUM> of the cross-over network <NUM> matches a predefined impedance. This is easier to achieve if high-pass filters and low-pass filters are used rather than band-pass filters, because the voltage standing wave ratio (VSWR) must meet particular criteria. Each of the filters implies a signal attenuation preferably as low as <NUM>,<NUM> to <NUM>,<NUM> dB.

A third splitting stage may be provided downstream the second splitting stage. The third splitting stage may comprise a plurality of composite dividers <NUM>', <NUM>" (in the embodiment there are four such dividers, one of them being referenced as such). A composite divider <NUM>', <NUM>" may comprise a series connection of a frequency-agnostic 3dB coupler <NUM>' (i.e., a power splitter) and a frequency-selective filter <NUM>", which jointly behave as a frequency-selective frequency divider.

The dividers <NUM>', <NUM>" of the third splitting stage are connected to the frequency dividers <NUM> of the second splitting stage directly or indirectly. The dividers of the third splitting stage may further include attenuators for levelling out any power level imbalances among the plurality of sub-bands, since the power levels of the sub-bands should be the same. The 3dB couplers <NUM>' increase an isolation between the sub-bands.

The third/last splitting stage may supply the respective sub-bands of the broadband signal to the plurality of output ports <NUM>. According to the example of <FIG>, eight sub-bands are available at the output ports <NUM> of the cross-over network <NUM>. Of course, a different number of sub-bands could be provided.

The cross-over network <NUM> may further comprise an amplifier <NUM> arranged between subsequent frequency dividers <NUM>, <NUM>', <NUM>" of the plurality of frequency dividers <NUM>. The attenuation added before an amplifier should be kept to a minimum. As such, preferably no power dividers (for example 3dB-couplers) or the like are used to split up the frequency before the use of an amplifier <NUM>. Instead, low-pass filters and/or high-pass filters should be used.

Between the first splitting stage and the second splitting stage, a pre-amplifier (not shown) such as a low-noise amplifier (LNA) may selectively be inserted into the signal path by means of switching devices. Such a pre-amplifier may be added after each frequency divider <NUM> of the first splitting stage.

Claim 1:
Measurement system (<NUM>) for a broadband signal, comprising
a cross-over network (<NUM>), including
an input port (<NUM>) for the broadband signal;
a plurality of output ports (<NUM>); and
a plurality of frequency dividers (<NUM>), being configured to supply respective sub-bands of the broadband signal to the plurality of output ports (<NUM>); and
a processing unit (<NUM>), being configured to analyze the respective sub-bands of the broadband signal concurrently;
the plurality of frequency dividers (<NUM>) comprising one or more of a low-pass filter and a high-pass filter.