Patent Description:
For high-precision measurements performed on a device under test by means of a measurement instrument, it is important to remove noise generated by sources other than the device under test.

For example, noise generated by a signal generator providing a test signal to the device under test and noise generated by the measurement instrument itself need to be taken into account.

There are different techniques known in the art that remove noise generated by sources other than the device under test. Document <CIT> discloses a system for measuring residual or additive phase noise added to input signal of e.g. two-port device under test and has processor for suppressing carrier of output signal by determining difference between output signal and reference signal.

The object of the present invention is to provide a signal processing method and a measurement system that further improve the noise cancelation of noise generated by sources other than the device under test.

According to the invention, the problem is solved by a signal processing method for reducing measurement uncertainties. The signal processing method comprises the steps of:.

Therein and in the following, the term "the device under test generates the analog measurement signal based on the analog reference signal" is understood to denote that the device under test may process and output the analog reference signal generated by an external signal generator.

Alternatively, this term may denote that the device under test processes and outputs the analog reference signal generated by a signal generator that is integrated into the device under test.

Further, the term "removing noise" is understood to denote that noise originating in the first measurement unit and/or in the second measurement unit is removed.

Therein, any suitable noise-cancellation technique may be used in order to remove the noise, as will be described in more detail below.

The noise-corrected measurement signal comprises noise generated by the device under test as well as noise generated by a signal generator generating the analog reference signal.

On the other hand, the noise-corrected reference signal comprises noise generated by the signal generator generating the analog reference signal.

Thus, when determining the difference signal, the noise generated by the signal generator cancels.

Thus, the resulting signal, i.e. the digital difference signal, comprises only noise generated by the device under test, particularly statistical noise generated by the device under test and noise due that originates from defects of the device under test.

In fact, the digital difference signal may only comprise noise generated by the device under test, i.e. no other signal components.

In other words, the digital difference signal corresponds to a DUT-specific error comprised in the digital measurement signal.

Thus, a performance of the device under test may be assessed based on digital difference signal. More precisely, the noise generated by the device under test may be analyzed based on the digital difference signal comprising only the noise generated by the device under test.

For example, the noise contribution of the device under test may be analyzed over frequency.

Thus, the signal processing method according to the present invention further reduces measurement uncertainties relating to noise generated by sources other than the device under test.

Accordingly, the signal processing method according to the present invention allows to assess the performance of the device under test with high precision, as an advanced noise cancelation of noise originating in all other sources is provided.

Consequently, additional measurement uncertainty is removed, which may originate from frequency response or non-linearities not caused by the device under test.

According to an aspect of the present invention, a signal level of the noise-corrected measurement signal and/or a signal level of the noise-corrected reference signal are/is adapted before determining the digital difference signal. By adapting the signal level of the noise-corrected measurement signal and/or the signal level of the noise-corrected reference signal, it is ensured that noise originating outside of the device under test cancels. Particularly, it is ensured that noise originating outside of the device under test cancels completely.

In an embodiment of the present invention, the signal level of the noise-corrected measurement signal and/or of the noise-corrected reference signal are/is adapted such that the noise-corrected measurement signal and the noise-corrected reference signal have a substantially equal signal level, particularly an equal signal level. By adapting the signal level of the noise-corrected measurement signal and/or the signal level of the noise-corrected reference signal this way, it is ensured that noise originating outside of the device under test cancels completely.

Therein, the term "substantially equal" is understood to denote that the signal levels are within <NUM>% of each other, particularly within <NUM>% of each other.

According to a further aspect of the present invention, the analog reference signal is generated based on a digital waveform. The digital waveform may be provided by means of a digital waveform generator.

In general, the digital waveform corresponds to a waveform that is to be applied to the device under test in order to assess the performance of the device under test.

In a further embodiment of the present invention, the digital waveform is forwarded to the first noise reduction unit and/or to the second noise reduction unit, wherein the noise is removed from the digital measurement signal and/or from the digital reference signal based on the digital waveform. This way, it is ensured that portions of the digital measurement signal and/or of the digital reference signal corresponding to the digital waveform are not removed when removing the noise.

Another aspect of the present invention provides that the digital waveform comprises a modulated signal and/or a continuous wave signal sweep. In fact, the digital waveform may correspond to an IQ data signal.

Particularly, the digital difference signal and the digital waveform are summed by means of a summation unit, thereby obtaining a digital summation signal. The resulting signal, i.e. the digital summation signal, comprises only the digital waveform and noise originating in the device under test.

According to another aspect the digital summation signal is provided to a measurement application.

In fact, a performance of the device under test may be assessed based on the digital summation signal. More precisely, the noise generated by the device under test may be analyzed, particularly by means of the measurement application, based on the digital summation signal comprising only the noise originating in the device under test and the digital waveform.

For example, the noise contribution of the device under test may be analyzed over frequency based on the digital summation signal.

In a further embodiment of the present invention, an impedance mismatch between a signal generator generating the analog reference signal and the device under test is corrected. Thus, unwanted reflections at an input port of the device under test are reduced, particularly avoided.

Therein, any suitable impedance-matching technique known in the state of the art may be used in order to correct the impedance mismatch.

Alternatively or additionally, an impedance mismatch between a signal generator generating the analog reference signal and the second measurement unit is corrected. Thus, unwanted reflections at the second measurement unit are reduced, particularly avoided.

According to the invention, the problem further is solved by a measurement system. The measurement system comprises a first measurement unit, a second measurement unit, a first noise reduction unit, a second noise-reduction unit, and a subtraction unit. The measurement system is configured to perform the signal processing method described above.

Regarding the further advantages and properties of the measurement system, reference is made to the explanations given above with respect to the signal processing method, which also hold for the measurement system and vice versa.

In an embodiment of the present invention, the first measurement unit, the second measurement unit, the first noise reduction unit, the second noise reduction unit, and the subtraction unit are integrated into a measurement instrument.

According to an aspect of the present invention, the measurement instrument is established as an oscilloscope, particularly as a digital oscilloscope, as a signal analyzer, as vector network analyzer, or as a measurement receiver.

However, it is to be understood that the measurement instrument may be established as any other suitable type of measurement instrument.

The measurement system may further comprise an external signal generator, wherein the external signal generator is configured to generate the analog reference signal, particularly based on a digital waveform.

Therein and in the following, the term "external" is understood to denote that the signal generator is established separately from the measurement instrument.

However, it is also conceivable that the signal generator is integrated into the measurement instrument.

<FIG> shows a measurement system <NUM> comprising a measurement instrument <NUM> and a device under test <NUM>.

In general, the measurement instrument <NUM> is configured to perform measurements on the device under test <NUM>, more precisely on electric signals received from the device under test <NUM>.

Therein, the device under test <NUM> may be any type of electronic device being configured to generate and/or process analog electric signals.

For example, the device under test <NUM> may be an amplifier, a mixer, a filter, a mobile phone, or any other electronic component or device being configured to generate and/or process an electric signal.

In the particular example shown in <FIG>, the device under test <NUM> is a two-port device that is configured to receive an analog signal from a signal generator <NUM>.

The device under test <NUM> processes the analog signal, thereby generating an analog measurement signal that is forwarded to the measurement instrument <NUM>.

However, it is to be understood that the device under test <NUM> may also be configured to generate the measurement signal.

In this case, the signal generator <NUM> may be integrated into the device under test <NUM>.

Further, it is also conceivable that the signal generator <NUM> may be integrated into the measurement instrument <NUM>.

In general, the type of the measurement instrument <NUM> may depend on the type of the device under test <NUM> to be tested.

For example, the measurement instrument <NUM> may be established as an oscilloscope, particularly as a digital oscilloscope, as a signal analyzer, as a vector network analyzer, or as a measurement receiver.

However, it is to be understood that the measurement instrument <NUM> may be established as any other suitable type of measurement instrument.

The measurement instrument <NUM> comprises a first measurement port <NUM> and a signal processing circuit <NUM> with a first measurement unit <NUM>, wherein the first measurement unit <NUM> is connected with an output of the device under test <NUM> via the first measurement port <NUM>.

The measurement instrument <NUM> further comprises a second measurement port <NUM> being connected with an output of the signal generator <NUM>.

The signal processing circuit <NUM> comprises a second measurement unit <NUM>, wherein the second measurement unit <NUM> is connected with the output of the signal generator <NUM> via the second measurement port <NUM>.

Therein and in the following, the term "unit" is understood to describe suitable hardware, suitable software, or a combination of hardware and software that is configured to have a certain functionality.

The hardware may, inter alia, comprise a CPU, a GPU, an FPGA, an ASIC, or other types of electronic circuitry.

The signal processing circuit <NUM> further comprises a first noise reduction unit <NUM> that is provided downstream of the first measurement unit <NUM> and a second noise reduction unit <NUM> that is provided downstream of the second measurement unit <NUM>.

Interconnected between the first noise reduction unit <NUM> and the second noise reduction unit <NUM>, a gain unit <NUM> is provided.

Further, a multiplication unit <NUM> is provided that is connected to the second noise reduction unit <NUM> downstream of the second noise reduction unit <NUM>, and that is connected to the gain unit <NUM> downstream of the gain unit <NUM>.

The measurement instrument <NUM> further comprises a subtraction unit <NUM> that is provided downstream of the first noise reduction unit <NUM> and downstream of the multiplication unit <NUM>.

The measurement system <NUM> may further comprise a digital waveform generator (DWG) <NUM>, which may be established separately from the signal generator <NUM>.

In this case, the signal generator <NUM> may be connected with the digital waveform generator <NUM> so as to receive a digital waveform generated by the digital waveform generator <NUM>.

However, it is also conceivable that the digital waveform generator <NUM> may be integrated into the signal generator <NUM> or into the measurement instrument <NUM>.

The signal processing circuit <NUM> may further comprise a digital waveform input <NUM> that is connected to the digital waveform generator <NUM>, e.g. via an additional input port of the measurement instrument <NUM>.

The first noise reduction unit <NUM> and the second noise reduction unit <NUM> may be connected to the digital waveform input <NUM> so as to receive the digital waveform generated by the digital waveform generator <NUM>.

The measurement instrument <NUM> may further comprise a summation unit <NUM> being connected to the subtraction unit <NUM> downstream of the subtraction unit <NUM> as well as being connected to the digital waveform input <NUM> so as to receive the digital waveform generated by the digital waveform generator <NUM>.

The signal processing circuit <NUM> may further comprise a signal output <NUM> that is connected to a measurement circuit <NUM>.

For example, the measurement circuit <NUM> may be configured to execute a measurement application being configured to analyze an output signal of the device under test <NUM> processed by the signal processing circuit <NUM>.

The functionality of the individual units and the other components of the measurement system <NUM> will be described in more detail below.

<FIG> shows a front view of the measurement instrument <NUM>.

As is illustrated in <FIG>, the measurement instrument <NUM> may comprise a display <NUM> that is configured to display a user interface and/or measurement data obtained by the measurement instrument <NUM>.

The measurement instrument <NUM> may further comprise input means <NUM>, e.g. buttons, a knob, a touch-sensitive display, etc..

In general, a user may control measurement settings of the measurement instrument <NUM> and/or may adjust the visualization of data on the display <NUM> via the input means <NUM>.

The measurement system <NUM> is configured to perform a signal processing method that is described in the following with reference to <FIG>.

A digital waveform is generated by means of the digital waveform generator <NUM> (step S1).

In general, the digital waveform corresponds to a signal that is to be applied to the device under test <NUM> in order to test the device under test <NUM>, i.e. in order to assess a performance of the device under test <NUM>.

For example, the digital waveform comprises a modulated signal and/or a continuous wave signal sweep.

Particularly, the digital waveform may correspond to an IQ data signal.

It is noted that in <FIG> digital signals are denoted by solid arrows, while analog signals are denoted by dashed arrows.

The digital waveform is forwarded to the signal generator <NUM>, to the first noise reduction unit <NUM>, and to the second noise reduction unit <NUM>.

An analog reference signal is generated by means of the signal generator <NUM> based on the digital waveform (step S2).

The analog reference signal is forwarded to the device under test <NUM> and to the second measurement unit <NUM>.

Therein, an impedance mismatch between the signal generator <NUM> and the device under test <NUM> may be corrected for by means of the signal generator <NUM> in order to minimize reflections at an input port od the device under test <NUM>.

Alternatively or additionally, an impedance mismatch between the signal generator <NUM> and the second measurement unit <NUM> may be corrected for by means of the signal generator <NUM> in order to minimize reflections at the second measurement port <NUM> of the measurement instrument <NUM>.

The analog reference signal is processed by means of the device under test <NUM>, thereby obtaining an analog measurement signal (step S3).

The analog measurement signal is forwarded to the first measurement unit <NUM>.

The analog measurement signal is digitized by means of the first measurement unit <NUM>, thereby obtaining a digital measurement signal (step S4).

Accordingly, the first measurement unit <NUM> may comprise at least one analog-to-digital converter being configured to digitize the analog measurement signal.

The analog reference signal is digitized by means of the second measurement unit <NUM>, thereby obtaining a digital reference signal (step S5).

Accordingly, the second measurement unit <NUM> may comprise at least one analog-to-digital converter being configured to digitize the analog reference signal.

Noise is removed from the digital measurement signal by means of the first noise reduction unit <NUM>, thereby obtaining a noise-corrected measurement signal (step S6).

Particularly, the noise is removed from the digital measurement signal based on the digital waveform provided by the digital waveform generator <NUM>.

The removed noise may correspond to noise generated by the measurement instrument <NUM>, particularly by the first measurement unit <NUM>.

Therein, any suitable noise-cancellation technique may be used in order to remove the noise from the digital measurement signal.

In a particular example, the noise may be removed as follows:
A DUT noise contribution of the device under test <NUM> to the digital measurement signal is determined.

The DUT noise contribution corresponds to noise originating in the device under test <NUM>.

The DUT noise contribution may be determined by means of any suitable technique, particularly by means of any suitable technique known from the state of the art. For example, the techniques described in granted US patent number <CIT> may be used in order to determine the DUT noise contribution.

Based on the determined DUT noise contribution and based on the digital waveform, a noise level of the digital measurement signal is reduced to a noise level of the DUT noise contribution, thereby obtaining the noise-corrected measurement signal.

Accordingly, the noise-corrected measurement signal comprises noise generated by the device under test <NUM> and noise generated by the signal generator <NUM>, as the noise generated by the measurement instrument <NUM> has been removed.

Noise is removed from the digital reference signal by means of the second noise reduction unit <NUM>, thereby obtaining a noise-corrected reference signal (step S7).

Particularly, the noise is removed from the digital reference signal based on the digital waveform provided by the digital waveform generator <NUM>.

The removed noise may correspond to noise generated by the measurement instrument <NUM>, particularly by the second measurement unit <NUM>.

Therein, any suitable noise-cancellation technique may be used in order to remove the noise from the digital reference signal.

For example, the noise may be removed analogously to step S7 described above, wherein the DUT noise contribution is replaced by a noise contribution of the signal generator <NUM> (in other words, the signal generator <NUM> corresponds to the DUT).

Accordingly, the noise-corrected reference signal comprises noise generated by the signal generator <NUM>, as the noise generated by the measurement instrument <NUM> has been removed.

A signal level of the noise-corrected reference signal is adapted by means of the gain unit <NUM> and by means of the multiplication unit <NUM> (step S8).

More precisely, the signal level of the noise-corrected reference signal is adapted such that the noise-corrected measurement signal and the noise-corrected reference signal have a substantially equal signal level, particularly an equal signal level.

The gain unit <NUM> may determine a signal level g<NUM> of the noise-corrected measurement signal and a signal level g<NUM> of the noise-corrected reference signal.

The gain unit <NUM> may determine a gain factor G based on the determined signal levels g<NUM>, g<NUM> according to G = g<NUM>/g<NUM>.

The signal level of the noise-corrected reference signal may then be adapted by means of the multiplication unit <NUM> by multiplying the noise-corrected reference signal with the gain factor G.

Of course, it is also possible to adapt the signal level of the noise-corrected measurement signal instead.

In this case, the signal level of the noise-corrected measurement signal may be adapted by means of the multiplication unit <NUM> by multiplying the noise-corrected measurement signal with the gain factor G' = g<NUM>/g<NUM>.

After adapting the signal level, the noise-corrected measurement signal and the noise-corrected reference signal are forwarded to the subtraction unit <NUM>.

A digital difference signal is determined by means of the subtraction unit <NUM> based on the noise-corrected measurement signal and based on the noise-corrected reference signal (step S9),.

More precisely, the subtraction unit <NUM> may subtract the noise-corrected reference signal from the noise-corrected measurement signal, thereby obtaining the digital difference signal.

Alternatively, the subtraction unit <NUM> may subtract the noise-corrected measurement signal from the noise-corrected reference signal, thereby obtaining the digital difference signal.

As already mentioned above, the noise-corrected measurement signal comprises noise generated by the device under test <NUM> and noise generated by the signal generator <NUM>, while the noise-corrected reference signal comprises noise generated by the signal generator <NUM>.

Thus, in the digital difference signal, the noise generated by the signal generator <NUM> cancels, such that the digital difference signal comprises only the noise generated by the device under test <NUM>.

In fact, as both the noise-corrected measurement signal and the noise-corrected reference signal comprise the digital waveform (and due to adapting the signal level of the noise-corrected reference signal and/or of the noise-corrected measurement signal), the digital waveform may cancel as well.

Thus, the digital difference signal may only comprise noise generated by the device under test <NUM>.

As indicated by the dotted arrow in <FIG>, the digital difference signal may be forwarded to the measurement circuit <NUM> for analysis of the noise generated by the device under test <NUM>, particularly for assessing the performance of the device under test <NUM>.

Further, the digital difference signal and the digital waveform may be summed by means of the summation unit <NUM>, thereby obtaining a digital summation signal (step S10).

The digital summation signal corresponds to the digital waveform, superposed with the noise generated by the device under test <NUM>.

The digital summation signal may be forwarded to the measurement circuit <NUM> for analysis of the noise generated by the device under test <NUM>, particularly for assessing the performance of the device under test <NUM>.

Certain embodiments disclosed herein, particularly the respective module(s) and/or unit(s), utilize circuitry (e.g., one or more circuits) in order to implement standards, protocols, methodologies or technologies disclosed herein, operably couple two or more components, generate information, process information, analyze information, generate signals, encode/decode signals, convert signals, transmit and/or receive signals, control other devices, etc. Circuitry of any type can be used.

Claim 1:
A signal processing method for reducing measurement uncertainties, the signal processing method comprising the steps of:
- receiving, by means of a first measurement unit (<NUM>), an analog measurement signal from a device under test (<NUM>);
- digitizing, by means of the first measurement unit (<NUM>), the analog measurement signal, thereby obtaining a digital measurement signal;
- removing, by means of a first noise reduction unit (<NUM>), noise from the digital measurement signal, thereby obtaining a noise-corrected measurement signal;
- receiving, by means of a second measurement unit (<NUM>), an analog reference signal, wherein the device under test (<NUM>) generates the analog measurement signal based on the analog reference signal;
- digitizing, by means of the second measurement unit (<NUM>), the analog reference signal, thereby obtaining a digital reference signal;
- removing, by means of a second noise reduction unit (<NUM>), noise from the digital reference signal, thereby obtaining a noise-corrected reference signal; and
- determining, by means of a subtraction unit (<NUM>), a digital difference signal based on the noise-corrected measurement signal and based on the noise-corrected reference signal.