WO2007090467A1

WO2007090467A1 - Detecting a transmission behavior by sampling a reflection signal

Info

Publication number: WO2007090467A1
Application number: PCT/EP2006/050801
Authority: WO
Inventors: Alexander Lazar; Marcus Mueller; Joachim Moll
Original assignee: Agilent Technologies, Inc
Priority date: 2006-02-09
Filing date: 2006-02-09
Publication date: 2007-08-16

Abstract

The invention relates to a device (100) for testing a device under test - DUT (116) by applying test signals and receiving response signals, comprising a signal generator (112, 14) for providing a probing signal to the DUT (116), a reflectometer circuit (10) for receiving from the DUT (116) a reflection signal in response to the probing signal, for sampling the reflection signal at a plurality of successive time points and determining comparison values by comparing the sample values each with a plurality of threshold values, and a processor (102) for deriving a transmission behavior of the transmission channel between the device (100) and the DUT (116) on the base of the comparison values.

Description

DETECTING A TRANSMISSION BEHAVIOR BY SAMPLING A

REFLECTION SIGNAL

BACKGROUND ART

[0001] The present invention relates to reflection measurements of a device under test - DUT.

[0002] Electrical systems comprising electrical networks and devices can be characterized and identified by measuring their electrical behavior in the frequency or in the time domain. The measurements in the time domain include time domain transmission (TDT) and time domain reflection (TDR) measurements.

[0003] For measuring reflections of an electrical system in the time domain, a pulse generator generates a test pulse signal which may be a step function or a short impulse. The test pulse signal is supplied to an input of the electrical system, e.g., to the input of a transmission line coupled at its output to DUT. The test pulse signal propagates through the transmission line to the DUT. If the terminating impedance of the transmission line, which is formed by the input impedance of the DUT, matches the transmission line characteristic impedance, the test pulse signal is absorbed and no reflection occurs.

[0004] However, in case of a mismatch between the terminating impedance and the transmission line characteristic impedance, the energy of the test pulse signal is at least partly reflected back to the input of the transmission line as an echo and added to the test signal. By analyzing the reflection signal resulting from adding the test signal and the echo at the input of the transmission line, the behavior of the electrical system in the time domain may be evaluated.

[0005] For the evaluation of the behavior of an electrical system in the time domain, a time domain reflectometer may be used, such as the TDR 8610OB lnfiniium DCA of the applicant. A time domain reflectometer contains a step generator for producing a positive-going incident wave which may be applied to a DUT. The algebraically addition of the incident wave and a reflected voltage wave may then be shown on an oscilloscope display of the time domain reflectometer. Thus, a traditional time domain reflectometer is a kind of oscilloscope adapted for the analysis of time domain reflections.

DISCLOSURE OF THE INVENTION

[0006] It is an object of the invention to provide improved reflection measurements. The object is solved by the independent claim(s). Preferred embodiments are shown by the dependent claim(s).

[0007] According to embodiments of the present invention, a device for performing accurate time domain measurements is provided. Particularly, embodiments of the invention may be implemented into output or input or analyzer parts of test instruments such as pulse data generators and bit error rate testers. A test instrument comprising an embodiment of the invention allows to quickly and easily measure the transmission behavior of a DUT in the time domain and to check a connection to a DUT, for example for impedance mismatches, transmission line failures, and skin effects. The measurements performed by embodiments of the invention may be used for determining several parameters of an electrical system, for example the s parameters, to characterize a transmission behavior, and finally to adjust a test instrument to the transmission behavior of an electrical system in order to obtain more accurate measurements.

[0008] An embodiment of a device of the invention for performing time domain measurements of a device under test - DUT, comprises a sender for providing a probing signal to the DUT, also referred to as test pulse signal, the probing signal exemplarily comprising a sequence of bits, said sequence forming a single pulse with a duration of one ore a plurality of the bits, a receiver for receiving a reflection signal from to the DUT in response to the probing signal, a sampling circuit for sampling the reflection signal at a plurality of successive sampling points, wherein each sampling point is defined by a time delay with respect to a reference time and a comparator for comparing values at least of a subset of the sampled values with different threshold values, and deriving a shape of the reflection signal.

[0009] In a further embodiment the probing signal is repetitively provided to the DUT. The reflection signal is sampled at a plurality of successive timing points within one repetition of the probing signal, whereby one of: the timing points are commonly shifted by a predefined time value by a predefined time increment the threshold is incremented by a predefined threshold increment, between two repetitions of the probing signal

[0010] In a further embodiment a two-dimensional grid of comparison values with respect to the sampling time points and the threshold values is obtained, wherein the grids are equally spaced with respect to the sampling time points and the threshold values.

[0011] In a further embodiment, a correction or adjusting signal is generated based on the derived transmission behavior. This correction signal is provided to the signal generator for shaping the test signals such that test signals provided by the test device are detected at the DUT with a desired shape. Such desired shape might be a shape that a signal would have if the transmission channel or the DUT interface had ideal properties.

[0012] Therefore, a signal shaping circuit might be provided for shaping the test signals. For example, the generated test signals may have a peak like signal such that droop behavior of a transmission channel may be compensated or it might have a certain rise time adjusted to compensate any impedance mismatches. A signal shaping unit for controlling a test signal generation with a signal shaping unit with respect to a desired transmission is described in the European patent application No. 06100624.3 of the same applicant.

[0013] Providing an automatic adjustment allows for implementing a fully automated DUT test without any need to disconnect the test equipment before a test and perform a transmission channel behavior test with a time domain reflecting unit. Further, this allows to continuously supervising, e.g. at defined equally spaced time instants, the transmission behavior between the test device and the DUT.

[0014] According to an embodiment of the invention, the processor may be adapted for controlling the sample point by controlling a delaying of the repetitive probing signal or the sampling time by a predefined delay and incrementing the threshold by a predefined threshold increment. By delaying the repetitive probing signal or the sampling time, the specific point in time of a sample point may be moved along the reflection signal waveform allowing taking samples consecutive in time. By incrementing the threshold, any peaks and droops of the reflection signal waveform may be detected.

[0015] According to a further embodiment of the device of the invention, the processor means may be adapted for generating a threshold setting signal for the receiver in order to vary the threshold in the receiver, a clock signal for clocking the sampling in the receiver, and a pulse generation control signal for the sender for setting the start time and amplitude of pulses contained in the repetitive probing signal.

[0016] According to a further embodiment of the device of the invention, the receiver may comprise a time domain reflectometer circuit with a probing signal input for receiving the repetitive probing signal, an amplifier having input lines connected to the probing signal input and output lines connected to an output of the time domain reflectometer circuit, comparator means having a signal input connected to the output of the time domain reflectometer circuit and a threshold input connected to a differential threshold setting input of the time domain reflectometer circuit, and a flip flop having a signal input connected to the output of the comparator means and a clock input connected to a clock setting input of the time domain reflectometer circuit.

[0017] According to a yet further embodiment of the device of the invention, the comparator means may comprise a single comparator and two switches controllable by a threshold switching input of the time domain reflectometer circuit, and each of the inputs of the single comparator may be connected to an output line of the output of the time domain reflectometer circuit or to a single threshold setting input by one of the two switches. [0018] According to a further embodiment of the device of the invention, the comparator means may comprise two comparators and a multiplexer, wherein the negative input of each of the two comparators is connected to the differential threshold setting input and the positive input of each of the two comparators is connected to one of the output lines, the output of each of the two comparators is connected to a respective input of the multiplexer, and the output of the multiplexer is connected to the signal input of the flip flop.

[0019] An embodiment of a test instrument of the invention comprises an embodiment of a device according to the invention for performing time domain measurements of a device under test. According to a further embodiment of the test instrument, the receiver may be implemented in the output or in the input or in the analyzer part of the test instrument. For example, the receiver may be integrated together with an output amplifier of the test instrument. According to a further embodiment of the test instrument of the invention, the test instrument may be a bit error ratio tester or a pulse data generator.

[0020] An embodiment of a method of the invention for performing time domain measurements of a device under test - DUT, comprises a) providing a repetitive probing signal to the DUT, b) receiving a reflection signal corresponding to the DUT response signal to the repetitive probing signal, c) comparing the reflection signal with a threshold and taking a sample of the comparison result at a sampling time, d) controlling a sample point of the reflection signal with respect to the threshold and the sampling time, e) repeating steps c) to d) for several times in order to obtain a set of samples, f) deriving a transmission behavior of the DUT in the time domain from the set of samples.

[0021] According to an embodiment of the invention, the method may further comprise generating adjusting signals with respect to the derived transmission behavior for controlling a test signal generation with a signal shaping unit with respect to a desired transmission behavior. As mentioned above, a signal shaping unit suitable for this purpose is disclosed in the European patent application no. 06100624.3 of the applicant.

[0022] According to an embodiment of the method of the invention, the controlling a sample point of the reflection signal with respect to the threshold and the sampling time comprises

- delaying the repetitive probing signal or the sampling time by a predefined delay, and

- incrementing the threshold by a predefined threshold increment.

[0023] According to an embodiment of the method of the invention, the predefined delay may be increased with the repetition of the repetitive probing signal in order to achieve a time information about the reflection signal.

[0024] According to an embodiment of the method of the invention, the threshold may be varied with the repetition in order to achieve an amplitude information about the reflection signal.

[0025] According to an embodiment of the method of the invention, the frequency of taking samples may correspond to the clock frequency with which the repetitive probing signal is generated.

[0026] According to an embodiment of the method of the invention, the predefined delay may be a fraction of a period of the repetitive probing signal.

[0027] Embodiments of the invention can be partly or entirely embodied or supported by one or more suitable software programs, which can be stored on or otherwise provided by any kind of data carrier, and which might be executed in or by any suitable data processing unit. Software programs or routines can be preferably applied to a test instrument comprising computing means in order to implement time domain measurements capabilities for deriving a transmission behavior of a DUT.

[0028] According to an embodiment of the invention, a software program implementing the method according to the invention may be further adapted for calculating s parameters from the derived transmission behavior of the DUT in the time domain.

BRIEF DESCRIPTION OF DRAWINGS

[0029] Other objects and many of the attendant advantages of embodiments of the present invention will be readily appreciated and become better understood by reference to the following more detailed description of embodiments in connection with the accompanied drawing(s). Features that are substantially or functionally equal or similar will be referred to by the same reference sign(s).

[0030] Fig. 1 shows a first embodiment of a time domain reflectometer circuit according to the invention;

[0031] Fig. 2 shows a second embodiment of a time domain reflectometer circuit according to the invention;

[0032] Fig. 3 shows a third embodiment of a domain reflectometer circuit according to the invention;

[0033] Fig. 4 shows an embodiment of a device for performing time domain measurements of a device under test according to the invention; and

[0034] Fig. 5 shows an exemplary waveform of a reflection signal with the thresholds and sampling points for performing a time domain measurement according to the invention.

[0035] Fig. 1 shows a time domain reflectometer circuit 10 which may be implemented in the output part of a test instrument in order to extend the test instrument with a time domain measurement capability. The test instrument may be for example a bit error rate tester - BERT - or a pulse/data generator. Such test instruments usually do not contain any time domain reflectometry measurement capability. By adding a time domain reflectometry measurement capability to such a test instrument, the handling of the instrument will be made easier since no extra time domain reflectometer is required for testing a connection line to a device under test - DUT. Instead, the built-in time domain reflectometer allows to test the connectivity between a BERT or a pulse/data generator and a DUT, for example, immediately before performing a test. Furthermore, the test instrument may test with the built-in time domain reflectometerforany impedance mismatches at the DUT, for example due to varying impedances of the connection to the DUT.

[0036] The time domain reflectometer circuit 10 is connected on its input side to the outputs of an amplifier 14 which may be the output amplifier of the test instrument. The amplifier 14 has a differential test pulse input 12 for receiving test pulses from a pulse generator (not shown) of the instrument. The amplifier 14 is a differential amplifier comprising a pair of npn Bipolar transistors T1 and T2. The differential input 12 of the amplifier is connected with the basis of the transistors T1 and T2. The emitter of the transistors T1 and T2 are connected to a current source I in order to lie on a predefined potential. Each collector of the transistors T1 and T2 is connected via a resistor R1 and R2, respectively, to a voltage VHIL. Amplifier 14 amplifies differential input signals such as test pulse signals from a pulse generator at its input 12 and provides the amplified signals at the output lines 18. The output lines 18 are connected to output lines 17 and 19 of the time domain reflectometer circuit 10. The output lines 17 and 19 are connected to the differential output 20 of the time domain reflectometer circuit 10 with which the DUT may be connected for example via a transmission line.

[0037] For measuring a reflection signal corresponding to the DUT response signal to a stimulating test pulse from the pulse generator and amplified by the amplifier 14, the time domain reflectometer circuit 10 comprises a receiver which comprises comparator means 22 and a flip flop 30.

[0038] The comparator means 22 comprise a single comparator 21 with a differential input "+" and "-" and a threshold input 26 connected to a threshold setting input 28 of the circuit 10. The inputs "+" and "-" of the comparator 21 are connected to two switches 36 or 38, forming an input 24 of the comparator means 22. Switch 36 is connected to the "+"-input of the comparator 21 , and switch 38 to the "-"-input of the comparator 21. Switch 36 allows to connect the "+"-input either to the output line 17 or a first threshold setting input Thresi 29. Switch 38 allows to connect the "-"-input either to the output line 19 or a second threshold setting input Thres2 31. The state of the switches 36 and 38 may be controlled by the threshold switching input 40. With the switches 36 and 38, the comparator means 22 may be operated in either a single or a differential measurement mode, as will be explained later in detail.

[0039] The output of the comparator 21 is connected to the signal input 32 of the flip flop 30 which is clocked via a clock signal on a clock input 34. The clock input 34 is connected to a clock setting input 36 which may receive a clock for sampling the comparison result of the comparator 21 provided on its output. The output of the flip flop 30 is connected to a measurement output 42 of the time domain reflectometer circuit 10.

[0040] Now, the operation of the time domain reflectometer circuit 10 is explained in detail. Circuit 10 may be operated in either a differential or a single ended measurement mode.

[0041] In the differential measurement mode, switches 36 and 38 connect the respective input "+" and "-" with the output lines 17 and 19, respectively, in order to receive a differential reflection signal occurring on the output 20 of the time domain reflectometer circuit 10. Furthermore, the threshold of the comparator 21 is set by a respective threshold setting signal supplied to the threshold setting input 28 of circuit 10. It should be noted that the threshold setting signal may be varied in order to obtain an accurate measurement result of the reflection signal, as will be explained later in detail. The threshold setting signal determines the voltage difference between the potentials on the two output lines 17 and 19. When the voltage difference between the two output lines 17 and 19 exceeds the voltage difference defined by the threshold setting signal, the output of the comparator 21 is switched from logical 0 to logical 1 , and vice versa.

[0042] In the single ended measurement mode, a differential reflection signal on either output line 17 or 19 may be measured. If the reflection signal on output line 17 should be measured, switch 36 is controlled to connect the input "+" of the comparator 21 with line 17 and switch 38 is controlled to connect the input "-" of the comparator 21 with the second threshold setting input Thres2 31. Then the signal on line 17 is compared to the threshold setting signal supplied to the second threshold setting input Thres2 31. If the reflection signal on output line 19 should be measured, switch 38 is controlled to connect the input "-" of the comparator 21 with line 19 and switch 36 is controlled to connect the input "+" of the comparator 21 with the first threshold setting input Thresi 29. Then the signal on line 19 is compared to the threshold setting signal supplied to the first threshold setting input Thresi 29. It should be noted that the threshold setting signal may be varied in order to obtain an accurate measurement result of the reflection signal, as will be explained later in detail.

[0043] In each measurement mode, the flip flop 30 is clocked with a clock signal received on the clock setting input 36. Thus, the sampled comparison results are supplied to the measurement output 42 for further processing.

[0044] It should be noted that the amplifier 14 and the time domain reflectometer circuit 10 may be implemented into an integrated circuit, for example an output driver circuit for a test instrument such as a BERT.

[0045] Fig. 2 shows a further time domain reflectometer circuit 50 which may also be implemented in the output part of a test instrument in order to extend the test instrument with a time domain measurement capability. Circuit 50 differs from circuit 10 of Fig. 1 in that two comparators 23 and 25 and a multiplexer 44 are applied instead of a single comparator 21 and the switches 36 and 38. Thus, circuit 50 may be only used for single ended measurements of signals on the output lines 17 and 19. The "+"-input of the first comparator 23 is connected to the output line 17 and the "+"-input of the second comparator 25 to the output line 19. The "-"-inputs of both comparators 23 and 25 are connected to a threshold input 26 connected with a threshold setting input 28 for receiving a threshold setting signal. Over the threshold setting input 28, the threshold may be adjusted with which the signals on the "+"-inputs of the comparators 23 and 25 are compared. The output signals of the comparators 23 and 25, i.e., the comparison results are guided to the inputs of the multiplexer 44 which allows to switch either of the received comparison results to the input 32 of the flip flop 30 A multiplexer control input 46 is provided for controlling which multiplexer input signal is routed to the multiplexer output. The flip flop 30 then samples the received comparison result in accordance with a clock received over the clock setting input 36. The sampled comparison results are supplied to the measurement output 42 for further processing. It should be noted that instead of the multiplexer 44 and the flip flop 30 also two flip flops may be provided, wherein each flip flop is associated with a respective comparator 23 and 25 and connected on its input side to the output of the associated comparator.

[0046] Instead of implementing the time domain reflectometer circuit according to the invention in the output part of a test instrument for performing time domain measurements of reflection signals from a DUTs connected to the test instrument's output channels, it may be also implemented in the analyzer part of a test instrument. This allows to measure the analyzer channel and any lines connected to the analyzer channel. Fig. 3 shows an analyzer 60 and a time domain reflectometer circuit 80 designed for the analyzer part of a test instrument. The time domain reflectometer circuit 80 receives over a differential analyzer input 74 a signal for example from a communication system. The received differential signal is guided over to input lines 70 and 72 to the analyzer 60. The analyzer 60 comprises a comparator 62. The inputs "+" and "-" of the comparator 62 may be connected over switches 64 and 63, respectively, with the input lines 70 and 72, respectively, or with threshold voltage VTHRES. For comparing a signal on line 70 with the threshold voltage VTHRES, switch 64 is closed so that the signal is conducted to the "+" and switch 63 is switched to the threshold voltage VTHRES so that the "-"-input receives the threshold voltage VTHRES. For comparing a signal on line 72 with the threshold voltage VTHRES, switch 63 is closed so that the signal is conducted to the "-" and switch 64 is switched to the threshold voltage VTHRES so that the "+"-input receives the threshold voltage VTHRES. The output signal of the comparator 62 is sampled with a flip flop 66 which is clocked with a clock signal 67. The sampled comparator output signal is provided at the analyzer output 68. In order to measure time domain reflections, the time domain reflectometer circuit 80 may generate a test pulse signal. The test pulse signal is generated by a flip flop 76 which is controlled over a test pulse generation input 77 and a test pulse generation clock input 78. The output signals of the flip flop 76 drive the basis of npn bipolar transistors T1 and T2 which are connected to form a differential amplifier. Thus, by providing suitable control signals at the inputs 77 and 78, a test pulse signal may be generated with the time domain reflectometer circuit 80. The test pulse signal is provided on the input lines 70 and 72. Any reflections caused by impedance mismatches in the system connected to the analyzer input 74 may then be analyzed with the analyzer 60.

[0047] Fig. 4 shows a device 100 for performing time domain measurements of a DUT 116. The device may be a test instrument or a module of a test instrument. It comprises a test pulse signal generator 112 for generating a repetitive test pulse signal 114, a time domain reflectometer circuit 10, for example as shown in Figs. 1 and 2, processor means 102 adapted for controlling the operation of the test pulse generator 112 and the time domain reflectometer circuit 10, a memory 118 for storing measurement values, and a display 120 for displaying measurement results. The test pulse generator 112 and the time domain reflectometer circuit 10 may be implemented in the output part of a test instrument.

[0048] The device 100 may be connected to a DUT 116 such as a high speed communication device. The processing means 102, for example implemented by a microcontroller or microprocessor, may execute a computer program stored in the memory 118. The computer program implements a method for performing time domain measurements of the DUT 116. The computer program adapts the processing means 102 so that it performs the following steps:

[0049] First, the processing means 102 control the test pulse generator 112 to generate a repetitive test pulse signal which is supplied to the DUT 116 via the time domain reflectometer circuit 10. If the electrical system comprising the wires for connecting the DUT 116 with the device 100 and the DUT 116 contains an impedance mismatch, energy of the test pulse signal is partly reflected back to the output of the device and added to the sent out test pulse signal. The resulting reflection signal corresponding to the DUT response signal to the repetitive test pulse signal 114 is compared with a threshold in the circuit 10. Furthermore, the circuit 10 takes a sample of the comparison result.

[0050] The control of the delay of pulses contained in the test pulse signal 114 and of the threshold in the circuit 10 by the processor means 102 may be performed as follows. In order to scan the reflection signal and to obtain an accurate measurement of the reflections signal, the processor means 102 control the test pulse generator 112 to delay the repetitive test pulse signal by a predefined delay, particularly a fraction of a period of the repetitive test pulse signal 114. Furthermore, the processor means 102 increment the threshold in the circuit 10 by a predefined threshold increment. The delay and threshold incrementing is repeated for several times in order to obtain a set of samples of the reflections signal which allows the processor means 102 to process a time domain measurement of the reflection signal from the set of samples. Instead of delaying the repetitive pulse signal sent out by the test pulse generator 112, also the delay of the clock for sampling the reflection signal in the circuit 10 may be controlled.

[0051] Fig. 5 shows an exemplary waveform 150 of a reflection signal composed of a pulse of a sent out test pulse signal and the reflection from an impedance mismatch. The reflection causes a kind of peak in the waveform. The pulse comprises a sequence of 6 bits. The bits have equal unit intervals Ul. Thus, period of a pulse is 6 Ul. As can be seen in Fig. 5, the pulse has a rising edge at the beginning of the Ul of the second bit (time t=1 in the shown diagram) and a falling edge at the beginning of the Ul of the fourth bit (time t=4 in the shown diagram). The reflection occurs between about the time t=2.5 and t=3. For generating the pulse, the processor means 102 control the test pulse signal generator 112, which may be implemented in the output part of the test instrument, to send out a bit sequence of 011100. The following table shows the capturing of data of the reflection signal with a varying threshold and a varying delay of sampling in each Ul of the reflection signal:

[0052] As can be seen from the above table, the peak caused by the reflection may be detected at a sampling time sc=0.75, i.e., when the sampling time is moved into the last quarter of an Ul, and with a threshold tc=2.5. The entire waveform may be constructed from the captured data by the processor means 102 and displayed on the display 120. The data may be captured either by first setting the threshold and then varying the delay or vice versa. For capturing the data as shown in the above table, 72 samples must be taken from the reflection signal. The repetitive test pulse signal generated by the test pulse signal generator 112 must send out at least 12 repetitions of the test pulse. The captured data may be stored in the memory 118 for later processing by the processor means or in an internal memory of the processor means 102 for immediate processing and displaying on the display 120. The captured data may also be further processed, for example in order to determine the S parameter of the DUT. Of course, it is possible to increase the sampling resolution by taking more samples per Ul, by reducing the increment steps of the delay of the sampling time and the threshold. Thus, the waveform may be determined with a very high accuracy.

[0053] Finally, it should be mentioned that the invention may be advantageously used with a signal shaping unit as described in the European patent application no. 06100624.3 of the applicant for implementing a fully automated test equipment. For example, such a test equipment may comprise a device for performing time domain measurements of a DUT according to this invention and a signal shaping unit as described in the before mentioned European patent application. The device according to the invention may be used to perform time domain measurements of the transmission behavior of the DUT. The, the device may process the measurements by deriving a transmission behavior and may further generate adjusting signals with respect to the derived transmission behavior. This means that, for example, the adjusting signals are generated in order to equalize a test signal generated by the signal shaping unit such that the desired transmission behavior may be simulated. Typically, the generation of the adjusting signals may be performed by a computer program implementing an algorithm for processing the time domain measurements performed by the device according to the invention. Particularly, the combination of the device according to the invention and of the signal shaping unit allows to pre-emphasize the test signal supplied to the DUT.

Claims

1. A device (100) for testing a device under test - DUT (116) by applying test signals and receiving response signals, comprising

- a signal generator (112, 14) adapted for providing a probing signal to the DUT (116),

- a reflectometer circuit (10) adapted for receiving from the DUT (116) a reflection signal in response to the probing signal, for sampling the reflection signal at a plurality of successive time points and determining comparison values by comparing the sample values each with a plurality of threshold values, and

- a processor (102) adapted for deriving a transmission behavior of the transmission channel between the device (100) and the DUT (116) on the base of the comparison values.

2. The device of claim 1 , wherein the signal generator (112, 14) is adapted for repetitively providing a probing signal to the DUT (116), and wherein the reflectometer circuit (10) is adapted for incrementing the threshold between two repetitions of the probing signal by a predefined threshold increment.

3. The device of claim 1 or 2, wherein the signal generator (112, 14) is adapted for repetitively providing a probing signal to the DUT (116), wherein the reflectometer circuit (10) is adapted for sampling the reflection signal at a plurality of successive timing points within one repetition of the probing signal, and wherein the timing points are shifted by a predefined time value between two repetitions of the probing signal by a predefined time increment.

4. The device of claim 1 or anyone of the above claims, wherein the reflectometer circuit (10) is adapted for determining a two-dimensional grid of comparison values with respect to the sampling time points and the threshold values, deriving a shape of at least a part of the probing signal from the comparison values, and deriving the transmission behavior therefrom.

5. The device of claim 4, wherein the transmission behavior is derived from a comparison of the derived shape and the shape of the probing signal.

6. The device of claim 1 or any one of the above claims, further being adapted to generate a correction signal (110) based on the derived transmission behavior and to provide the correction signal to the signal generator (14, 112) for shaping the test signals for at least partly compensating the transmission behavior with respect to a desired transmission behavior.

7. The device of claim 1 , comprising a test pulse input (12) for receiving the probing signal (114), an amplifier (14) having input lines (16) connected to an input (12) adapted to be connected to a signal source, and output lines (18) connected to an output (20) adapted to be connected to the DUT (116).

8. The device of claim 7, wherein the amplifier is adapted for adjusting its amplification behavior with respect to the derived transmission behavior.

9. The device of claim 7, further comprising, a comparator circuit (22) having a signal input (24) connected to the output (20) and a threshold input (26) connected to a threshold setting input (28), and a flip flop (30) having a signal input (32) connected to the output of the comparator means (22) and a clock input (34) connected to a clock setting input (36).

10. The device of claim 9, wherein the comparator circuit (22) comprises one comparator having two inputs and two switches (36, 38) controllable by a threshold switching input (40), that alternatively switches each of the two inputs of the single comparator (21 ) to one of the output lines (17, 19) of the output (20) or to each a threshold setting input (29, 31 ).

11. The device of claim 9, wherein the comparator circuit (22) comprise two comparators (23, 25) and a multiplexer (40), wherein the negative input of each of the two comparators (23, 25) is connected to a differential threshold setting input (28) and the positive input of each of the two comparators (23, 25) is connected to one of the output lines (17, 19), the output of each of the two comparators (23, 25) is connected to a respective input of the multiplexer (40), and the output of the multiplexer (40) is connected to the signal input (32) of the flip flop (30).

12. A method for performing measurements of a device under test - DUT, comprising:

- providing a probing signal to the DUT(116)

- receiving a reflection signal in response to the probing signal from the DUT

(116),

- sampling the reflection signal at a plurality of successive time points for obtaining sample values,

- determining comparison values by comparing the sample values with a plurality of different threshold values each for a plurality of sample values of successive time points, and

- deriving a transmission behavior of the transmission channel between the device (100) and the DUT (116) on the base of the comparison values.

13. A software program or product, preferably stored on a data carrier, for controlling an execution of the method of claim 12, when run on a data processing system such as a computer.