Patent Publication Number: US-2022236318-A1

Title: Automated test equipment comprising a device under test loopback and an automated test system with an automated test equipment comprising a device under test loopback

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of copending International Application No. PCT/EP2020/083412, filed Nov. 25, 2020, which is incorporated herein by reference in its entirety. 
    
    
     DESCRIPTION 
     Embodiments according to the invention are related to automated test equipments comprising a device under test loopback for testing a device under test which is connected to the automated test equipment via a load board. Further embodiments according to the invention are related to automated test systems comprising an automated test equipment and a load board for testing a device under test. 
     Integrated radio frequency (RF) devices often consist of a transmitter and a receiver. An output of the transmitter and an input of the receiver are often connected to independent RF pins of the integrated RF device. In an automated test, those pins are connected to individual ports of the automated test equipment (ATE). So the transmitter and receiver of the integrated RF device or the device under test (DUT) are tested independently and/or individually by stimulus and measurement modules or resources of the ATE. 
     According to a prior art example, the ATE contains stimulus and measurement resources or modules. The resources of the ATE are connected to unidirectional tester ports of the ATE. Those ports are configured to connect to a device under test (DUT), so the ATE may stimulate the DUT receiver or measure signals transmitted from the DUT transmitter. 
     According to another example, similar to the example before, the ATE modules, e.g. the stimulus and measurement resources, are connected to the tester ports of the ATE. Using additional switches, each tester port may be connected either to a stimulus or a measurement resource of the ATE, enabling a bi-directional usage of the ports. The DUT could be connected to the ATE bi-directional in one way, or the other way around. That is, for example, the transmitter of the DUT may be connected to a first port of the ATE and the receiver of the DUT may be connected to a second port of the ATE. Or the transmitter and receiver of the DUT may be swapped, so that the receiver of the DUT may be connected to the first port of the ATE and the transmitter of the DUT may be connected to the second port of the ATE. 
     There is a need for an ATE which performs tests more efficiently by utilizing the available resources. 
     An embodiment of the present invention is an automated test equipment (ATE) for testing a device under test (DUT) which is connected to the ATE via a load board. The ATE comprises a stimulus module, a measurement module, a loopback, a first switch, a second switch, and a load board interface. The load board interface comprises a first radio frequency port and a second radio frequency port. The first and second radio frequency ports are configured to be coupled to the respective ports of the load board. The first switch is configured to couple the first radio frequency port to the stimulus module in a first switching state of the first switch and the second switch is configured to couple the second radio frequency port to the measurement module in a first switching state of the second switch. Further, the first switch is configured to couple the first radio frequency port to a first end of the loopback in a second switching state of the first switch and the second switch is configured to couple the second radio frequency port to a second end of the loopback in a second switching state of the second switch. When the first and second switches are in their respective second switching state, a loopback signal path is formed between the first and second radio frequency ports. 
     The above-described embodiment of an ATE allows for the ATE to test the receiver of the DUT with the stimulus module of the ATE and/or to test the transmitter of the DUT with the measurement module of the ATE or allows a DUT self-test depending on the switching states of the first and second switches. In a DUT self-test or loopback test the transmitter of the DUT transmits a signal to the receiver of the DUT, in order to stimulate the receiver of the DUT. A typical frequency of a test signal in a loopback test is between 1 MHz and 100 GHz. Thus, providing the ATE with the loopback enables utilizing internal self-test resources of the DUT when the DUT is coupled to the ATE via the load board, without requiring an external loopback or a loopback within the load board. 
     In other words, when the first and second switches are in their respective second switching states, a direct loopback connection or a loopback signal path is formed or introduced between the RF ports. The loopback signal path allows to connect the transmitter of the DUT to the receiver of the DUT, enabling DUT loopback testing. So the internal resources of the DUT may be used for self-testing the DUT. The loopback or the loopback signal path may operate in both directions. 
     A self-test of the DUT could be executed in ‘mission mode’, supported by the functionalities of the transmitter or receiver of the DUT, or by using built-in self-test functionalities of the DUT. The internal resources of the DUT might have additional functionality or better performance parameters than the ATE enabling more thorough tests. When the loopback or the loopback signal path is not used, the ATE stimulus and measurement modules or resources may still be connected to the DUT via the switches and may be used for executing additional tests. 
     In a preferred embodiment, the load board interface comprises pogo pins configured to connect digital and power supply pins to the load board. The pogo pins may be used for their improved durability over other electrical contact forms, and for the resilience of their electrical connection to mechanical shocks and vibrations. 
     According to embodiments, the first and second radio frequency ports of the load board interface are coaxial ports. RF coaxial cables are used for minimizing signal loss and interference. An advantage of coaxial over other types of radio transmission lines is that in an ideal coaxial cable the electromagnetic field carrying the signal exists only in the space between the inner and outer conductors. This allows, for example, a coaxial cable to be installed next to metal objects without power losses that would occur in other types of transmission lines. A coaxial cable also provides protection of the signal, for example, from an external electromagnetic interference. Coaxial connectors are designed to maintain a coaxial form across the connection and have the same impedance as the attached cable. Due to the skin effect, the RF signal is only carried by deflating at higher frequencies and does not penetrate to the connector body. 
     In an embodiment, the loopback comprises a transmission line directly connecting the first switch to the second switch. The loopback comprising a transmission line directly connecting the first switch to the second switch is configured to connect the receiver of the DUT to the transmitter of the DUT over the transmission line, if the first and the second switch are in the second switching state. That is, the signal of the transmitter of the DUT is directly measured by the receiver of the DUT, enabling a DUT self-test. 
     In an embodiment, the loopback comprises at least one power adjusting element. The power of the signal transmitted by the transmitter of the DUT may differ from the input range of the receiver of the DUT, therefore a power adjusting element may be used to adapt the power ranges. The power delivered by the transmitter of the DUT may be adjusted by the power adjusting element to a level that is suitable for the receiver of the DUT. 
     In an embodiment, the loopback comprises at least one of an attenuator and an amplifier as the power adjusting element. As the physical characteristics of the transmitter and the receiver of the DUT differs, a power adjusting element, such as an attenuator and/or an amplifier, may be used. For example, in RF applications the transmitter of the DUT tend to be a high power transmitter, while the receiver of the DUT tend to be a highly sensitive receiver. With an attenuator the power of the signal provided by the transmitter of the DUT may attenuated to a level that is suitable for the receiver of the DUT. On the contrary, when the input power range of the receiver of the DUT is higher than the power of the signal provided by the transmitter of DUT, an amplifier may amplify the signal to a level that is suitable for the receiver of the DUT. 
     In an embodiment, the loopback is a first loopback permitting signal transmission between the first and second radio frequency ports in a first direction and the ATE comprises a second loopback permitting signal transmission between the first and second radio frequency ports in a second direction opposite to the first direction. The first switch is configured to couple the first radio frequency port to a first end of the second loopback in a third switching state of the first switch, and the second switch is configured to couple the second radio frequency port to a second end of the second loopback in a third switching state of the second switch. The loopback signal path is formed between the first and second radio frequency ports when the first and second switches are in the respective third switching state. Such embodiments permit a bi-directional operation via the loopback and the second loopback. This permits a bi-directional operation in case of loopbacks permitting unidirectional signal transmission only, such as a loopback including a power amplifier element. The second loopback may also comprise power adjusting elements, which may permit unidirectional signal transmission, such as in a direction opposite to the signal transmission direction of the first loopback. 
     According to embodiments, the ATE comprises at least one coupler configured to couple out parts of a signal from the loopback signal path and to provide the coupled out part of the signal to the measurement module of the ATE. The coupler may be a directional coupler. The coupler may enable the ATE to receive, store and analyze the parts of the data coupled out by the coupler. For example, if the tested DUT would fail one of the tests, the signal transmitted by the DUT may be still measured and/or collected and/or analyzed by the ATE. In addition, such a coupler enables analyzing the loopback signal by the ATE simultaneously with the loopback test. 
     In an embodiment, a first coupler is configured to couple out part of a signal from a portion of the loopback signal path between the power adjusting element and the first radio frequency port and to provide the coupled out part of the signal to the measurement module. A second coupler is configured to couple out part of the signal from a portion of the loopback signal path between the power adjusting element and the second radio frequency port and to provide the coupled out part of the signal to the measurement module. In other words, the first and second couplers or directional couplers are configured to couple out part of the signal before and after the power adjusting elements and to provide the coupled out parts of the signal to the measurement module of the ATE. This enables the ATE to collect and/or store and/or analyze the transmitted signal of the transmitter of the DUT before and after the power adjusting element. For example, if the tested DUT would fail one of the tests, the signals transmitted by the DUT may be still measured and/or collected and/or analyzed by the ATE. 
     In an embodiment, the ATE comprises a coupler switch which is configured to couple the first coupler or the second coupler to the measurement module. In case the ATE comprises more than one coupler or directional coupler, a coupler switch may be used to choose which coupler is connected to the measurement module of the ATE, enabling reading out and/or storing and/or analyzing coupled out parts of the signal timely sequenced, using one coupler after each other. 
     In an embodiment, the first switch is configured to couple the first radio frequency port to the measurement module in a fourth switching state of the first switch and the second switch is configured to couple the second radio frequency port to the stimulus module in a fourth switching state of the second switch. The fourth switching states of the first and second switches enable the ATE to stimulate the receiver of the DUT with a stimulation module of the ATE and/or to measure the transmitted signal of the DUT by a measurement module of the ATE, enabling a bi-directional operation of the ATE. 
     According to embodiments, the ATE comprises a third switch configured to couple the first switch to the stimulus module when the first switch is in the first switching state of the first switch and to couple the second switch to the stimulus module when the second switch is in the fourth switching state of the second switch. Further, the ATE comprises a fourth switch configured to couple the second switch to the measurement module when the second switch is in the first switching state of the second switch and to couple the first switch to the measurement module when the first switch is in the fourth switching state of the first switch. In other words, the third switch is configured to couple the stimulus module with the first switch or with the second switch, and the fourth switch is configured to couple the measurement module to the first switch or to the second switch. The stimulus module of the ATE may stimulate a receiver of the DUT via the first or the second RF port, depending on the switching states of the switches, and also the measurement module of the ATE may measure a transmitted signal of the transmitter of the DUT over the first or second RF port depending on the switching states of the switches. Therefore, by using the third and the fourth switch a bi-directional operation of the DUT is enabled. 
     A further embodiment comprises an automated test system comprising an automated test equipment and a load board. The load board is configured to be mechanically and electrically docked to the load board interface of the ATE and the load board comprises at least one socket configured to accommodate a DUT. The connectors of the socket configured to be connected to the DUT are connected to the first and second radio frequency ports of the ATE via the load board. The load board of the automated test system enables a high speed switching of DUTs and is adapted to a production environment. Further, the applied load board may be switched out swiftly to a new load board, compatible with a different type of DUTs. Therefore using a load board in the automated test system enables testing different DUTs fast and convenient in a production environment. 
     It should be noted that features and functionalities of the automated test system may be supplemented by any of the features, functionalities and details which are described herein with respect to the automated test equipment, both individually and taken in combination. 
     Further, it should be noted that the numbering of the switches and the numbering of the switching states are chosen arbitrary and used as a distinction from the already mentioned switches or switching states respectively. 
    
    
     
       In the following, embodiments of the present disclosure are described in more detail with reference to the Figures in which: 
         FIG. 1  shows a schematic representation of an automated test equipment with a device under test loopback connected to a device under test via a load board, according to an embodiment; 
         FIG. 2  shows a schematic representation of an automated test equipment connected to a device under test, according to the prior art; 
         FIG. 3  shows a schematic representation of a bi-directional automated test equipment connected to a device under test, according to the prior art; 
         FIG. 4  shows a schematic representation of a bi-directional automated test equipment with a device under test loopback connected to a device under test via a load board, according to an embodiment; 
         FIG. 5  shows a schematic representation of a bi-directional automated test equipment with a device under test loopback comprising an attenuator connected to a device under test via a load board, according to an embodiment; 
         FIG. 6  shows a schematic representation of a bi-directional automated test equipment with two device under test loopbacks, each comprising an attenuator and an amplifier, connected to a device under test via a load board, according to an embodiment; 
         FIG. 7  shows a schematic representation of a bi-directional automated test equipment with couplers and with a device under test loopback comprising an attenuator connected to a device under test via a load board, according to an embodiment; 
         FIG. 8  shows a schematic representation of a bi-directional automated test equipment with couplers and with two device under test loopbacks, each comprising an attenuator and an amplifier, connected to a device under test via a load board, according to an embodiment; 
         FIG. 9  shows a view of a test head of an automated test equipment comprising a load board interface, according to an embodiment; 
         FIG. 10  shows views of parts of an automated test equipment connecting a radio frequency interface module to the radio frequency card of the automated test equipment; 
         FIG. 11A  shows a top view of an example of a load board without load board printed circuit board (PCB); 
         FIG. 11B  shows a bottom view of an example of a load board; 
         FIG. 11C  shows a load board with load board PCB installed. 
     
    
    
     In the following, different inventive embodiments and aspects of an automated test equipment (ATE) will be described. Also, further embodiments will be defined by the enclosed claims. It is to be noted that the same or similar elements in the Figures are provided with the same reference signs and that a repeated description of such elements and the functionality thereof is omitted. Thus, the description of an element with a specific reference sign in connection with one of the Figures also applies for the corresponding element in connection with other Figures. 
     It should be noted that any embodiments as defined by the claims may be supplemented by any of the details, features and functionalities described herein. Also, the embodiments described herein may be used individually, and may also optionally be supplemented by any of the details, features and functionalities included in the claims. It should also be noted that individual aspects described herein may be used individually or in combination. Thus, details may be added to each of said individual aspect without adding details to another one of said aspects. It should also be noted that the present disclosure describes explicitly or implicitly features useable in an automated test equipment or in an automated test system. Thus, any of the features described herein may be used in the context of an automated test equipment or an automated test system. 
     The invention will be understood more fully from the detailed description given below and from the accompanying drawings of embodiments of the invention which, however, should not be taken to limit the invention to the specific embodiments described, but are for explanation and understanding only. 
       FIG. 1  shows a schematic representation of an embodiment of an automated test equipment (ATE)  110  with a loopback, configured to test a device under test (DUT)  130  connected to the ATE  110  via a load board  120 . The ATE  110  comprises a stimulus module  140 , a measurement module  150 , a loopback  160 , a first switch  173 , a second switch  176  and a load board interface  180 . The load board interface further comprises a first radio frequency port  183  and a second radio frequency port  186 . 
     The ATE  110  is connected to the DUT  130  via the load board  120 . The load board  120  is coupled to the ATE  110  over the load board interface  180 . The load board interface  180  comprises, for example, pogo pins configured to connect digital data pins and power supply pins to the load board  120 , and the first and second radio frequency ports  183 ,  186 , such as coaxial ports, to be coupled with the respective ports of the load board  120 . 
     Within the ATE  110  the first radio frequency port  183  is coupled to the first switch  173  and the second radio frequency port  186  is coupled to the second switch  176 . The first switch  173  is coupled to the first radio frequency port  183 , to the stimulus module  140 , and to a first end of the loopback  160 . The second switch  176  is coupled to the second radio frequency port  186 , to the measurement module  150  and to a second end of the loopback  160 . Unless otherwise stated, the term coupled as used herein means that the corresponding elements are connected, such as directly, to each other so that signal transmission may take place therebetween. 
     The first switch  173  is configured to couple the first radio frequency port  183  with the stimulus module  140  in a first switching state or to couple the first radio frequency port  183  to a first end of the loopback  160  in a second switching state. The second switch  176  is configured to couple the second radio frequency port  186  to the measurement module  150  in a first switching state or to couple the second radio frequency port  186  to a second end of the loopback  160  in a second switching state. In the Figures, switching states of the switches are indicated by Roman numerals. 
     When the first and second switches  173 ,  176  are in the respective second switching state, a loopback signal path  170  is formed between the first and second radio frequency ports  183 ,  186 . To be more specific, the loopback signal path  170  is formed by loopback  160  and signal lines coupling high frequency port  183  to first switch  173  and high frequency port  186  to second switch  176 . 
     Generally, the loopback signal paths described herein may be regarded as being formed by a respective loopback and signal lines connecting respective switches to the high frequency ports. Generally, the loopback and the signal lines may comprise any transmission line or waveguide suitable for high frequency signal transmission, such as microstrip lines formed by a conductive trace and a nearby ground plane, microstrip lines formed by a conductive trace sandwiched between two nearby conductive traces, or coplanar lines. 
     The above-described setup makes it possible for the ATE  110  to test the receiver  193  of the DUT  130  by stimulating the receiver  193  using the stimulus module  140  of the ATE  110  when the first switch  173  is in the first switching state. Further, it allows for the ATE  110  to measure the signal from the transmitter  196  of the DUT  130  using the measurement module  150  of the ATE  110  if the second switch  176  is in the first switching state. This setup also allows for the ATE  110  to couple the transmitter  196  of the DUT  130  with the receiver  193  of the DUT  130  using the loopback signal path  170  if both switches, the first switch and the second switch  173 ,  176 , are in the respective second switching state. In this state loopback tests may be executed and executing loopback tests may save ATE resources and/or enable the ATE  110  to utilize the additional functionalities and/or the good performance parameters of the DUT  130  resulting in a more thorough test. 
       FIG. 2  shows a schematic representation of a prior art ATE  210  coupled to a DUT  230 . The ATE  210  comprises a stimulus module  240 , a measurement module  250 , a first RF port  283  and a second RF port  286 . Within the ATE  210  the stimulus module  240  is coupled to the first radio frequency port  283  and a measurement module  250  is coupled to the second radio frequency port  286 . The DUT  230  comprises a receiver  293  and a transmitter  296 . The receiver  290  of the DUT  230  is coupled to the stimulus module  240  of the ATE  210  over the first radio frequency port  283  of the ATE  210 . The transmitter  296  of the DUT  230  is coupled to the measurement module  250  of the ATE  210  over the second radio frequency port  286  of the ATE  210 . The stimulus module  240  of the prior art ATE  210  is configured to test the receiver  293  of the DUT  230  by stimulating the receiver  293  which is coupled to the stimulus module  240  of the ATE  210  over the first radio frequency port  283 . The measurement module  250  of the ATE  210  is configured to test the transmitter  296  of the DUT  230  by measuring the signal transmitted by the transmitter  296 , which is coupled to the measurement module  250  of the ATE  210  over to a second radio frequency port  286 . 
     The internal resources of the DUT  230  may have additional functionalities or better performance parameters when compared to the ATE  210 . The prior art ATE  210  does not permit effective utilization of such available resources of the DUT. 
       FIG. 3  shows a schematic representation of a bi-directional prior art ATE  310  coupled to a DUT  330 . Similar to the prior art ATE  210  of  FIG. 2 , the prior art ATE  310  comprises a first radio frequency port  383 , a second radio frequency port  386 , a stimulus module  340  and a measurement module  350 . Further, the prior art ATE  310  comprises additional four switches, when compared to the prior art ATE  210 : a first switch  373 , a second switch  376 , a third switch  363 , and a fourth switch  366 . 
     The ATE  310  is coupled to the DUT  330 , which comprises a receiver  393  and a transmitter  396 , over the first and second RF ports  383 ,  386 . The receiver  393  is coupled to the first radio frequency port  383 . The transmitter  396  is coupled to the second radio frequency port  386 . Analogously to the ATE  210 , the stimulus and receiver modules  340 ,  350  of the ATE  310  are configured to test the respective receiver and transmitter modules  393 ,  396  of the DUT  330 . 
     Within the ATE  310  the first radio frequency port  383  is coupled to the first switch  373 , while the second radio frequency port  386  is coupled to the second switch  376 . Both, the first switch  373  and the second switch  376  are coupled to the third switch  363  and to the fourth switch  366 . The third switch  363  is coupled to the stimulus module  340 . The fourth switch  366  is coupled to the measurement module  350 . 
     Within the ATE  310  the stimulus and the measurement modules  340 ,  350  are configured to be coupled to the first or to the second radio frequency port  383 ,  386  depending on the switching states of the additional four switches  363 ,  366 ,  373 ,  376 . 
     The stimulus module  340  may be coupled to the first radio frequency port  383  when the first and third switches  363 ,  373  are both in their first switching states. The stimulus module  340  may be coupled to the second radio frequency port  386  when the third switch and the second switch  363 ,  376  are both in their second switching state. 
     The measurement module  350  may be coupled to the second radio frequency port  386  when the fourth switch and the second switch  366 ,  376  are both in their first switching state. The measurement module  350  may be coupled to the first radio frequency port  383  when the fourth switch and the first switch  366 ,  373  are both in their second switching state. 
     The additional four switches  363 ,  366 ,  373 , and  376  enable a bi-directional operation of the first and second ports  383 ,  386 , that is the receiver  393  may be connected to the first radio frequency port  383  and the transmitter  396  of the DUT  330  may be connected to the second radio frequency port  386 , as shown in  FIG. 3 , if the four switches are in the first switching state. Moreover, the receiver  393  may be connected to the second radio frequency port  386  and the transmitter  396  may be connected to the first radio frequency port  383  if the switches are in the respective second switching state. Thus, the ports are bi-directional and connection of the transmitter  396  and the receiver  393  of the DUT  330  may be swapped. 
     Compared to the prior art ATE  210 , the prior art ATE  310  permits a bi-directional operation, but neither of the ATE  210  nor the ATE  310  provides any support for utilizing available DUT resources, such as self-test resources of the DUT. 
       FIG. 4  shows a schematic representation of an embodiment of a bi-directional ATE  410  comprising a loopback  460 . The ATE  410  is coupled to a DUT  430  via a load board  420  over the load board interface  480  of the ATE  410 . The ATE  410  is a sophisticated version of the ATE  110  of  FIG. 1  and comprises four switches, a first switch  473 , a second  476 , a third switch  463  and a fourth switch  476 . The four switches  466  permit a bi-directional operation of the ATE  410 . 
     The first radio frequency port  483  is coupled to the first switch  473 , the second radio frequency port  486  is coupled to the second switch  476 . Both, the first switch  473  and the second switch  476  are coupled to the third switch  463  and to the fourth switch  466 . The first switch  473  is further coupled to the second switch  476  via loopback  460 . 
     Within the ATE  410  the stimulus module  440  is coupled to the third switch  463  and the measurement module  450  is coupled to the fourth switch  466 . The stimulus and the measurement modules  440 ,  450  are configured to be coupled to the first or to the second radio frequency port  483 ,  486  depending on the switching states of the four switches  463 ,  466 ,  473 ,  476 . 
     The stimulus module  440  may be coupled to the first radio frequency port  483  when the first and third switches  463 ,  473  are both in their first switching states. The stimulus module  440  may be coupled to the second radio frequency port  486  when the third switch and the second switch  463 ,  476  are both in their second switching state. 
     The measurement module  450  may be coupled to the second radio frequency port  486  when the fourth switch and the second switch  466 ,  476  are both in their first switching state. The measurement module  450  may be coupled to the first radio frequency port  483  when the fourth switch and the first switch  466 ,  473  are both in their second switching state. 
     Due to the four switches  463 ,  466 ,  473 ,  476  of the ATE  410  the first and second radio frequency ports  483  and  486  of the load board interface  480  are bi-directional, that is either one of the receiver  493  and the transmitter  496  of the DUT  430  may be connected to one of the first and second radio frequency ports  483 ,  486  and the other one of the receiver  493  and the transmitter  496  may be connected to the other one of the first and second radio frequency ports  483 ,  486 , depending on the switching states of the four switches. The stimulus module  440  is configured to test the receiver  493  of the DUT and the measurement module  450  is configured to test the transmitter  496  of the DUT  430  based on a signal transmitted by the transmitter  496  and received at the measurement module  450 . 
     If both, the first and the second switch  473 ,  476  are in their third switching state, the first radio frequency port  483  is connected to the second radio frequency port  486  via the loopback  460  and a loopback signal path  470  is formed between the first and second RF ports  483 ,  486 . The loopback signal  470  path enables loopback testing of the DUT  430 , that is the receiver  493  of the DUT  430  is receiving the signal transmitted by the transmitter  496  of the DUT  430  via the loopback signal path  470 . The loopback or the loopback signal path  470  may operate in both directions. A typical signal used in the loopback testing may have a frequency between 1 MHz and 100 GHz. 
       FIG. 5  shows a schematic representation of an embodiment of a bi-directional ATE  510  with a loop back  460  comprising an attenuator  570 . The ATE  510  is coupled to the DUT  430  via the load board  420 . The ATE  510  corresponds to the ATE  410  shown in  FIG. 4  except for the fact that loopback  460  of ATE  510  comprises an attenuator  570  while loopback  460  of ATE  410  provides a direct connection between radio frequency ports. Thus, with respect to all other elements and features reference is made to the above description with respect to  FIG. 4  and a repeated description is omitted. The additional attenuator  570  may be a fixed or a variable attenuator, which may be adjusted continuously or step by step. The attenuator  570  allows to adjust an insertion loss of the loopback  460 , so that the power delivered by the transmitter  496  of the DUT  430  may be attenuated to a level that is suitable for the receiver  493  of the DUT  430 . The loopback signal path  470  is formed between the first and the second RF ports  483 ,  486  when the first and second switch  473 ,  476  are in their third switching state. The loopback signal path  470 , comprising the attenuator  570 , remains bi-directional, that is it may operate in both directions with the attenuator  570 . 
       FIG. 6  shows a schematic representation of an embodiment of a bi-directional ATE  610  with two loopbacks  460   a  and  460   b , each comprising an attenuator and an amplifier. The ATE  610  is connected to the DUT  430  via load board interface  480 . In ATE  610  the first and second switches  473 ,  476  may be coupled to each other via either the first loopback  460   a  or the second loopback  460   b . Both loopbacks  460   a ,  460   b  comprise an attenuator  570   a ,  570   b  and an amplifier  690   a  and  690   b . In an alternative embodiment, one or both of the attenuators  570   a ,  570   b  may be omitted. Attenuators  570   a ,  570   b  may be fixed or variable attenuators, which may be adjusted continuously or step by step. 
     The attenuators  570   a ,  570   b  and/or the amplifiers  690   a ,  690   b  are examples of power adjusting elements and permit the power delivered by the transmitter  496  of the DUT  430  to be either amplified or attenuated to a level that is suitable to the receiver  493  of the DUT  430 . 
     In this embodiment, the first switch  473  has four switching states and the second switch  475  has four switching states. A first loopback signal path  470   a  is formed by the first loopback  460   a  between the first radio frequency port  483  and the second radio frequency port  468  when the first switch and the second switch  473 ,  476  are both in the third switching state. Since the first loopback  460   a  comprises the attenuator  570   a  and the amplifier  690   a , it permits a unidirectional signal transmission in a first direction from the second switch  475  to the first switch  437 . 
     Since an amplifier is usually an unidirectional component, the second loopback  460   b  providing the second loopback signal path  470   b  is provided in order to permit a bi-directional operation. The second loopback signal path  470   b  is formed by the second loopback  460   b  between the first and second RF ports  483 ,  486  when the first switch and the second switches  473 ,  476  are both in their fourth switching state. The second loopback  460   b  comprises the second attenuator  570   b  and the second amplifier  690   b  and permits signal transmission in a second direction from the first switch  473  to the second switch  475 , which is opposite to the first direction. 
       FIG. 7  shows a schematic representation of an embodiment of a bi-directional ATE  710  comprising loopback  460  provided with the attenuator  570  and coupler  733 ,  736 . ATE  710  is connected to DUT  430  via load board  420 . ATE  710  shown in  FIG. 7  is corresponds to ATE  510  in  FIG. 5  except for couplers  733 ,  736 , coupler switch  730  and the fact that the fourth switch has a third switching state. Couplers  733 ,  736  are connected to coupler switch  730 . The first and second couplers  733 ,  736  are coupled to coupler switch  330  and coupler switch  330  is further coupled to fourth switch  466 . When fourth switch  466  is in the third switching state, it couples measurement module  450  with coupler switch  730 . 
     The first and second couplers  733 ,  736  are configured to couple out part of a signal from a portion of the loopback signal path  470  which is formed between the first and second RF ports  483 ,  486 . The coupler switch  730  is configured to couple the first coupler  733  or the second coupler  736  to the measurement module  450  when the fourth switch  466  is in the third switching state. 
     The couplers  733 ,  736  may be directional couplers each configured to couple out part of the signal propagating in first direction or a second direction. Coupler switch may be configured to couple fourth switch  466  to a specific one of four coupler terminals depending on which part of the signal is to be coupled out to the measurement module. 
     Thus, couplers  733 ,  736  enable the ATE  710  to receive and/or store and/or analyze parts of the signal propagating on the loopback signal path  470 . For example, if the tested DUT  430  would fail one of the tests, the transmitted signals of the DUT  430  may be still measured and/or collected and/or analyzed by the ATE  710 . 
     In other words, by adding couplers  733 ,  736 , the loopback signal may be coupled out and fed into the measurement module  450  of the ATE  710 . The couplers  733 ,  736  enable analyzing the loopback signal of the loopback signal path  470  by the ATE  710  simultaneously to the loopback test. The loopback signal could also be coupled out at other coupling paths of the couplers using switch  730 . For example, the couplers may be directional couplers. The loopback  460  may be implemented with or without the attenuator  570 . 
       FIG. 8  shows a schematic representation of a bi-directional ATE  810  connected to a DUT  430  via a load board  420 , wherein ATE  810  comprises couplers  733 ,  736  and two loopbacks  460   a ,  460   b , each comprising an attenuator  570  and an amplifier  690 . Thus, ATE  810  corresponds to ATE  610  shown in  FIG. 6  with the exception that couplers  733 ,  736  and coupler switch  730  are provided and that fourth switch  466  comprises an additional third switching state. Both, the first coupler and the second coupler  733 ,  736  are coupled to the coupler switch  730 , which is further coupled to the fourth switch  466 . When the fourth switch  466  is in the third switching state it couples measurement module  450  with coupler switch  730  so that the signal coupled out from the loopback path, either  470   a  or  470   b , is transferred to the measurement module  450 . 
     The first and second switches  473  and  476  permit switching the first loopback  460   a  into the loopback path so that loopback path  470   a  is formed or switching the second loopback  460   b  into the loopback path so that loopback path  470   b  is formed. Each of the loopbacks  460   a ,  460   b  comprises an unidirectional amplifier  690   a ,  690   b  and, therefore, forms an unidirectional loopback. The first loopback  460   a  permits a signal transmission in a first direction, while the second loopback  460   b  permits a signal transmission in a second direction, opposite to the first direction. In addition, each of the loopbacks  460   a ,  460   b  comprises an attenuator  570   a ,  570   b . In other embodiments, one or both attenuators  570   a ,  570  may be omitted. 
     The first and second couplers  733 ,  736  are configured to couple out part of a signal from a portion of the first or second loopback signal paths  470   a ,  470   b . In examples, couplers  733 ,  736  are configured to couple out part of a signal from a common portion of the first and second loopback signal paths  470   a ,  470   b , such as the signal line connecting high frequency port  483  to first switch  473  and the signal line connecting high frequency port  486  to the second switch  476 . The coupler switch  730  is configured to couple one of the terminals of the first coupler  733  or one of the terminals of the second coupler  736  to the measurement module  450  when the fourth switch  466  is in the third switching state. Thus, signals propagating in the respective loopback signal path in different directions may be coupled to the measurement module  450 . 
     The added couplers  733 ,  736  might be directional couplers enabling the ATE  810  to receive and/or store and/or analyze parts of the signal coupled out by the couplers  733 ,  736 . For example, if the tested DUT  430  would fail one of the tests, the transmitted signals of the DUT  430  may be still measured and/or collected and/or analyzed by the ATE  810 . 
     While two couplers are shown in  FIGS. 7 and 8  in connection with specific loopbacks, it is to be noted that a different number of couplers, such as only one coupler, may be provided. In addition, one or more couplers may be used in connection with any of the loopbacks disclosed herein. In  FIGS. 7 and 8 , the couplers are provided at portions of the loopback path between the respective radio frequency port and the first or second switch. In other embodiments, one or more couplers may be provided to couple out part of the signal directly from the respective loopback, i.e. from the signal path between the first and second switches. 
       FIG. 9  shows a view of a test head  900  of an ATE, such as the ATE in any of the embodiments described herein. The test head  900  and, therefore, the ATE comprises a load board interface  930  comprising coaxial radio frequency interfaces  920  and digital and power supply interfaces  910 . A load board may be mechanically and electrically docked to the load board interface  930 . The digital and power supply interface  910  comprises digital data pins and power supply pins  915 . The digital data pins and power supply pins  915  are configured to connect directly to a load board printed circuit board (PCB) shown in  FIG. 11 , for example, via pogo-pins. The coaxial RF interface  920  comprises one or more radio frequency interface modules  950 . The radio frequency interface module  950  is configured to be connected with the load board via coaxial cable interface, in order to transmit and/or receive radio frequency signals. 
       FIG. 10  shows an example of a radio frequency interface module  950  comprising radio frequency ports  1010 , which are, for example, coaxial cable ports. The radio frequency interface module (RFIM)  950  may be connected to a radio frequency card  1030  of the ATE via radio frequency cabling  1020 . Generally, the DUT loopback may be implemented within an appropriate portion of the ATE, such as in test head  900 , in radio frequency interface module  950  or in RF card  1030 . Since the DUT loopback is implemented in the ATE, any change or modification in the load board or additional components of the load board are not necessary for the implementing of the DUT loopback. 
       FIGS. 11A to 11C  show views of an example of a load board  1110 . The load board  1110  may comprise a load board frame, a coaxial interface and a load board printed circuit board (PCB).  FIG. 11A  shows a top view of the load board frame without the load board PCB, i.e. the load board PCT is not installed in  FIG. 11A . The coaxial cables  1120  shown in  FIG. 11A  are connected to connectors on the load board PCB, which are close to a DUT. 
       FIG. 11B  shows a bottom view of the load board  1110 , when the load board PCB  1160  is not installed. The coaxial cables  1120  of  FIG. 11B  are connected to a coaxial interface  1130  of the load board  1110 . The coaxial interface may be configured to be connected to a radio frequency interface module (RFIM), such as one of the radio frequency interface modules  950  shown in  FIG. 9 . The load board with an installed load board PCB  1160  is shown in  FIG. 11C . DUTs are located in sockets on the other side of the load board PCB  1160 . The positions of DUT sockets  1150  and connectors  1120  to the coaxial cables  1120  are marked in  FIG. 11C . 
     According to the present teaching, a DUT loopback which permits connection of a DUT transmitter to a DUT receiver is provided in the ATE, i.e. not in the load board or the DUT itself. Thus, internal resources of the DUT may be used for self testing the DUT. Since the loopback is provided in the ATE, the load board does not need any change or additional components. In embodiments, the loopback and the features to implement the respective loop back path may be provided within a RFIM or a RF card of the ATE. 
     Although some aspects have been described as features in the context of an apparatus it is clear that such a description may also be regarded as a description of corresponding features of a method. Although some aspects have been described as features in the context of a method, it is clear that such a description may also be regarded as a description of corresponding features concerning the functionality of an apparatus. 
     In the description, it may be seen that various features are grouped together in embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may lie in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the description, where each claim may stand on its own as a separate embodiment. While each claim may stand on its own as a separate embodiment, it is to be noted that, although a dependent claim may refer in the claims to a specific combination with one or more other claims, other embodiments may also include a combination of the dependent claim with the subject matter of each other dependent claim or a combination of each feature with other dependent or independent claims. Such combinations are proposed herein unless it is stated that a specific combination is not intended. Furthermore, it is intended to include also features of a claim to any other independent claim even if this claim is not directly made dependent to the independent claim. 
     The above described embodiments are merely illustrative for the principles of the present disclosure. It is understood that modifications and variations of the arrangements and the details described herein will be apparent to others skilled in the art. It is the intent, therefore, to be limited only by the scope of the pending patent claims and not by the specific details presented by way of description and explanation of the embodiments herein.