Patent ID: 12259425

DETAILED DESCRIPTION OF THE EMBODIMENTS

1. Circuit According to FIG.1

FIG.1shows a block schematic diagram of a circuit for calibrating a plurality of ATE channels, according to embodiments of the present invention. The circuit100comprises a first ATE channel110and a second ATE channel120. Although the circuit100is described with reference to two ATE channels110,120for ease of explanation, it is appreciated that the circuit100can be extent to any number of ATE channels. The circuit further comprises a central measurement unit130which is configured to provide a current to a selected one of the ATE channels (e.g., to an ATE channel which is activated while one or more other ATE channels are deactivated). Alternatively or in addition, the central measurement unit is configured to measure a current from (e.g., provided by or enforced by) a selected one of the ATE channels (e.g., from an ATE channel which is activated while one or more other ATE channels are deactivated). Moreover, the central measurement unit comprise a central measurement port132, which is coupled to the plurality of ATE channels110,120by (e.g., via) respective diodes112,122, which are circuited (e.g., arranged) between the central measurement port132of the central measurement unit and respective DUT ports111,121of the ATE channels110,120.

For example, a first diode112can be coupled between the DUT port111of the first ATE channel110and the central measurement port132. Likewise, a second diode122can be coupled between the DUT port121of the second ATE channel120and the central measurement port. The first diode112and the second diode122can be arranged in the same orientation.

In a calibration mode, the central measurement unit130may be configured to provide a predetermined (e.g., precisely adjustable) current at its central measurement port130. For this purpose, the central measurement unit130may, for example, comprise a precisely adjustable current source. Moreover, voltage levels of the ATE channels110,120may be adjusted such that the first diode112is conductive (e.g., forward biased) while the second diode122is non-conductive (e.g., blocked or reversed-biased). Accordingly, by appropriately biasing the second diode122, it may be ensured that no (or no significant) current is flowing through the second diode122. Consequently, the current provided by the central measurement unit130flows into the first ATE channel110via the first diode112. On the basis of the predetermined current provided by the central measurement unit through the first diode112, a calibration of the first ATE channel110may be performed.

In a further calibration step, the biasing conditions may be exchanged, such that the second diode122is conductive while the first diode112is non-conductive (e.g., blocked or reversed biased). Consequently, the current provided by the central measurement unit130flows into the second ATE channel121via the second diode122. On the basis of the predetermined current provided by the central measurement unit130through the second diode122, a calibration of the second ATE channel may be performed.

Accordingly, it is apparent that by adjusting the biasing conditions of the diodes112,122, it can be determined which of the ATE channels110,120is effectively coupled to the central measurement unit130. Consequently, individual ones of the ATE channels110,120can be calibrated.

In another calibration mode, a provision of a predetermined current by an ATE channel and a measurement of said current by the central measurement unit is also possible. For example, the first ATE channel110may be configured to provide a current and the second ATE channel120may be configured (e.g., programmed) such that the second diode120is in a non-conductive (e.g., blocking or reverse-biased) state. Thus, the current provided on the first ATE channel110may flow to the central measurement unit130via the first diode112and the central measurement port132, and may be measured by the central measurement unit130. Accordingly, a calibration may be performed on the basis of the measurement of the current. By appropriately biasing the second diode122, it can be ensured that the current provided by the first ATE channel can be individually measured by the central measurement unit, even though the first ATE channel110and the second ATE channel120are both coupled to the central measurement port via diodes.

To conclude, it becomes apparent that an appropriate biasing of the diodes112,122, which are circuited between the ATE channels110,120and the central measurement port, allows for effectively coupling a selected individual ATE channel110,120to the central measurement unit, in order to perform a calibration of the ATE channel.

Moreover, it should be noted that the concept as described inFIG.1may optionally be extended to a larger number of ATE channels. Furthermore, it should be noted that the ATE channels110,120may, for example, be part of an automated test equipment. The ATE channels may, for example, be adjustable or programmable under the control of a test program, which may be executed by a test program executor. Moreover, the ATE channels110,120may, for example, be part of a channel module, which may be a module that comprises a plurality of ATE channels. However, an automated test equipment may comprise a very large number of ATE channels, e.g., of the order of hundreds or even thousands of ATE channels. The ATE channels110,120may comprise different functionalities. For example, the ATE channels may comprise a programmable current source or a programmable active load. Alternatively or in addition, the ATE channels may comprise a measurement unit which may, for example, perform a current measurement.

For example, the measurement unit may be part of a “parametric measurement unit” which can measure characteristics of inputs and/or of outputs (e.g., generally speaking, of pins) of a device under test DUT. In particular, it should be noted that the DUT ports111,121are typically adapted to be coupled to a device under test, or to a load board which comprises a DUT socket for contacting a device under test.

To conclude, the circuit100for calibrating a plurality of ATE channel is well-suited for usage in an automated test equipment and allows for a calibration of a plurality of ATE channels without using relays associated with the individual ATE channels.

Moreover, the circuit100may optionally by supplemented by any of the features, functionalities and details disclosed herein, both individually and taken in combination. Also, any of the features, functionalities and details described with respect to the circuit100may optionally be introduced into any other embodiments disclosed herein, both individually and taken in combination.

2. Circuit According to FIG.2

FIG.2shows a block schematic diagram of a circuit200for calibrating a plurality of ATE channels, according to embodiments of the present invention. The circuit200comprises a plurality of ATE channels220,230,240,250and a central measurement unit260. The circuit200also comprises a first connection network270and a second connection network280.

The first ATE channel220comprises, for example, a DUT port221, which is adapted to be coupled to a pin of a device under test. Moreover, the first ATE channel220comprises a first calibration connection224and a second calibration connection226. The first calibration connection224is coupled to the first connection network, and the second calibration connection is coupled to the second connection network280. Moreover, the first connection network270and the second connection network280are coupled to a central measurement port262of the central measurement unit260via a relay290. For example, the relay290may couple the central measurement port262selectively to the first connection network270and to the second connection network280.

In the following, details regarding the first ATE channel220will be described. However, it should be noted that the other ATE channels230,240,250may, for example, be identical to the first ATE channel220.

The first ATE channel220comprises an ATE pin electronics (ATE PE)224, a DUT connection224aof which is coupled to the DUT port221. Moreover, a positive supply connection224bof the ATE pin electronics may be coupled to a positive supply voltage VCC, and a negative supply voltage connection224cof the ATE pin electronics224may be coupled to a negative supply voltage VEE (which may, for example, be negative when compared to the first supply voltage VCC). The ATE channel220also comprises a first series connection of two diodes228a,228b, wherein an anode of the first diode228amay be coupled to the DUT connection224a, wherein a cathode of the first diode228amay be coupled to an anode of the second diode228band wherein a cathode of the second diode228bmay be coupled to the positive supply voltage VCC. A node, which is coupled to the cathode of the first diode228aand to the anode of the second diode228bmay, for example, also be coupled to the first connection network270. Similarly, the first ATE channel220comprises a second series connection comprising a third diode228cand a fourth diode228d. An anode of the third diode228cis coupled to the negative supply voltage VEE, and a cathode of the third diode228cis coupled to an anode of the fourth diode228d. A cathode of the fourth diode228dis coupled to the DUT terminal224a. Accordingly, it can be said that the first connection network is coupled to a tap of the first series connection of diodes228a,228b, and that the second connection network280is coupled to a tap of the second series connection of diodes228c,228d.

It should be noted that the second ATE channel230, the third ATE channel240and the fourth ATE channel250may have a similar structure like the first ATE channel220. In particular, it should be noted that the second ATE channel also comprises a first calibration connection234and a second calibration connection236. The third ATE channel also comprises a first calibration connection244and a second calibration connection246. Similarly, the fourth ATE channel250also comprises a first calibration connection254and a second calibration connection256. It should be noted that the first calibration connections224,234,244,254of the ATE channels220,230,240250are all coupled to the first connection network270. For example, the first calibration connections224,234,244,254may all be directly coupled to the same conductive trace which forms the first connection network270(e.g., without any additional switches in between). Similarly, the second calibration connections226,236,246,256of the different ATE channels may all be coupled to the same conductive structure that forms the second connection network280. For example, the second calibration connections226,236,246,256may all be directly coupled (e.g., without any switches in between) with the conductive structure or conductive strip forming the second connection network280.

In the following, an example of the operation of the circuit200will be described.

In a first case (or setting), a current provided by a selected one of the ATE channels, for example, provided by the first ATE channel220, is measured by the central measurement unit. For this purpose, the relay290is configured to connect the central measurement port262of the central measurement unit260with the first connection network270. The selected ATE channel, in this case the first ATE channel220, is configured to provide a desired current (e.g., set to a desired setting value). For this purpose, an output voltage of the first ATE channel220may be adjusted in such a manner that the first diode228abecomes conductive. For this purpose, a potential which is present at the central measurement port262of the central measurement unit260is also adjusted to be such that the diode228ais forward biased. At the same time, the diode228bshould be reversed biased. Furthermore, voltages at the DUT ports of the other, non-selected ATE channels are, for example, adjusted to be such that their respective diodes238a,248a,258aare reversed bias. Accordingly, there is no current flow from the other, non-selected ATE channels230,240250to the first connection network270. Rather, by an appropriate adjustment of the potentials, it can be ensured that only the diode228ais forwarded biased, and that only the first ATE channel220provides a current to the first connection network270. The current provided to the first connection network270by the first ATE channel220is then measured by a measurement unit of the central measurement unit260.

Accordingly, it is apparent that an appropriate biasing of the diodes228a,238a,248a,258a, and also of the other diodes, allows to effectively only have a single ATE channel coupled with the central measurement unit260(in the above example, the first ATE channel220). Thus, a measurement of the current provided by the selected ATE channel (e.g., the first ATE channel220) is possible, which allows for a calibration of said ATE channel.

Naturally, it is possible to subsequently calibrate all ATE channels be changing the biasing conditions (e.g., such that the first diode228aof the first ATE channel220is reversed biased (e.g., blocking) and one of the other first diodes238a,248a,258aof one of the other ATE channels is forward biased (e.g., conducting).

In another case (or setting), the central measurement unit260provides a current, for example, using a precise and preferably adjustable current source. In this case, the central measurement port262of the central measurement unit260may, for example, be coupled to the second connection network280. Moreover, the ATE pin electronics224,234,244,254of the ATE channels220,230,240,250may be set in such a manner that only for a selected one of the ATE channels, a diode228d,238d,248d,258dbetween the second connection network and the DUT port is conducting (e.g., forward-bias). For example, if the first ATE channel220is selected, the pin electronics224of the first ATE channel220is configured (or programmed) such that the diode228dis conductive. For this purpose, a potential at the central measurement port262of the central measurement unit260is also set to a proper value, which allows for such a biasing of the diode228d. In contrast, the pin electronics234,244,254of the other ATE channels (i.e., of the non-selected ATE channels) is set such that the diodes238d,248d,258dbetween the second connection network280and the DUT ports231,241,251of the other ATE channels230,240,250is non-conductive (e.g., blocked or reversed-biased). Accordingly, the typically well-defined current provided by the central measurement unit260is forwarded, e.g., by the relay and the second connection network280, to only a single, selected ATE channel via the (then forward-biased) diode228dthat is coupled between the second connection network and the DUT port221of the selected ATE channel220. In contrast, a current flow from the second connection network towards the DUT connections231,241,251of the other ATE channels is prevented by the (then) reverse biased diodes238d,248d,258d. Accordingly, the current provided by the central measurement unit260can be forwarded to a single selected ATE channel, which allows for a calibration of the selected ATE channel.

Naturally, it is possible to subsequently calibrate all ATE channels be changing the biasing conditions (e.g., such that the fourth diode228dof the first ATE channel220is blocked and one of the other fourth diodes238d,248d,258dof one of the other ATE channels is forward biased.

As an additional remark, it should be noted that the diodes228b,238b,248b,258bare typically non-conductive during calibration, but allow for an overvoltage protection.

Similarly, during normal operation, the first series connection of diodes228a,228bprovides for an overvoltage protection at the DUT connection221(since overvoltages are limited to the sum of the forward voltages of diodes228a,228b).

The same also holds for the diodes coupled between the respective DUT ports and the respective negative supply voltage. For example, diodes228c,238c,248c,258care normally non-conductive during the calibration, but provide for an under-voltage protection.

During normal operation the second series connection of diodes228c,228dalso provides for an under-voltage protection at the DUT connection221, since the voltage at the DUT connection221is typically limited to fall below the negative supply voltage VEE by no more than a sum of the forward voltages of diodes228c,228d.

To conclude, the circuit200allows for a calibration of an individual, selected ATE channel without having switches or relays associated with each individual ATE channel. Rather, there is only one switch or relay290which selectively connects the central measurement port262of the central measurement unit with the first connection network270or with the second connection network280. A selection of an individual ATE channel for a calibration is done, for example, by properly adjusting operational states of all ATE channels that are coupled to the central measurement unit260. For example, potentials at the central measurement port262of the central measurement unit260and at the DUT connections221,231,241,251are set in such a manner that only one of the ATE channels is effectively coupled to a central measurement unit, thereby allowing a selective calibration of a selected ATE channel.

However, it should be noted that the circuit200may optionally be supplemented by any of the features, functionalities, and details disclosed herein, also with respect to the other embodiments, both individually and taken in combination. Moreover, it should be noted that any of the features, functionalities, and details of the circuit200may optionally be introduced in any of the other embodiments disclosed herein, both individually and taken in combination.

3. Circuit According to FIG.3

FIG.3shows a block schematic of a circuit300for calibrating a plurality of ATE channels, according to embodiments of the present invention. The circuit300comprises a plurality of ATE channels320,330,340,350. It should be noted that the circuit300is very similar to the circuit200according toFIG.2. For example, the circuit can comprise a first ATE channel320, which corresponds to the first ATE channel220, second ATE channel330which corresponds to the ATE channel230, a third ATE channel340which corresponds to the ATE channel240and a fourth ATE channel350, which corresponds to the ATE channel250. The circuit300also comprises a central measurement unit360which corresponds to the central measurement unit260, a first connection network370which corresponds to the first connection network270and a second connection network380which corresponds to the second connection network280. Moreover, the circuit300also comprises a relay390which corresponds to a relay290.

Moreover, it should be noted that the ATE channels320,330,340,350are very similar to the ATE channels220,230,240,250. For example, the first ATE channel320comprises a first series circuit of a first diode328aand a second diode328b. A tap between the first diode328aand the second diode328bis coupled (e.g., without any switch in between) with the first connection network370. Moreover, the first ATE channel320also comprises a second series connection comprising a third diode328cand a fourth diode328d. A tap between the third diode328cand the fourth diode328dis coupled (e.g., without a switch in between) with the second connection network380. Insofar, the first ATE channel320is similar to the first ATE channel220, such that the above discussion also applies.

However, it should be noted that, in addition to the circuitry of the ATE channel220, the ATE channel320further comprises a first switch229awhich is circuited in parallel to the second diode328b, which allows to short circuit the second diode328b. Moreover, the ATE channel320also comprises (in addition to the features of the ATE channel220) a second switch329b, which is circuited in parallel to the third diode328cand which allows to short circuit the third diode328c.

Similarly, the other ATE channels comprise switches339a,339b,349a,349b,359a,359b. It should be noted that, during calibration, the switches329a,329b,339a,339b,349a,349b,359a,359bare normally open (e.g., non-conductive). Accordingly, the switches329a,329b,339a,339b,349a,349b,359a,359bdo not affect a calibration of the ATE channels. For example, at least those of the switches329a,329b,339a,339b,349a,349b,359a,359bcoupled with the currently used connection network (e.g., out of the connection networks370,380) are open (non-conductive) when a calibration is performed. Accordingly, the respective non-short circuited diodes (out of the diodes328b,338b,348b,358b,328c,338c,348c,358c) serve as overvoltage protection or as undervoltage protection.

For example, those of the switches329a,329b,339a,339b,349a,349b,359a,359bwhich are coupled to the currently non-used connection network (out of the first connection network370and the second connection network380) may optionally be closed (e.g., conductive) to tie the currently non-used connection network to a well-defined potential. However, this functionality may be considered as optional.

Accordingly, the switches329a,329b,339a,339b,349a,349b,359a,359bdo not negatively affect a calibration and may even, optionally, help to tie a non-used connection network out of the connection networks370,380to a predefined potential, which may help to reduce cross talk.

Moreover, when the automated test equipment is not in a calibration mode, switches329a,329b,339a,339b,349a,349b,359a,359bmay, for example, be closed (e.g., conductive) to thereby short circuit the respective diodes. In this case, the connection networks370,380are tied to well-defined potentials, which may help to avoid cross talk. Moreover, an improved overvoltage protection or undervoltage protection for the DUT connections321,331,341,351may be provided, since there is only one diode (rather than a series connection of two diodes) between the respective DUT connection and the supply rails providing the positive supply voltage (e.g., VCC) and the negative supply voltage (e.g., VEE).

To conclude, the circuit300allows to perform an efficient calibration of the ATE channels. For the calibration, the same procedure as described above with respect toFIG.2can be used, wherein, during calibration, all switches329a,329b,339a,339b,349a,349b,359a,359b, or at least those switches which are coupled to the currently used connection network380or390, are open. During normal operation, i.e., when the automated test equipment is testing a device under test, pins of which are coupled to the DUT connections321,331,341,351, the switches may, for example, be closed, thereby providing improved overvoltage protection and undervoltage protection while keeping a cross talk between different ATE channels small.

However, it should be noted that the circuit300according toFIG.3may optionally be supplemented by any of the features, functionalities and the details disclosed herein, also with respect to other embodiments, both individually and taken in combination. Moreover, it should be noted that any of the features, functionalities and details disclosed with respect to the circuit300may optionally be introduced in any of the other embodiments disclosed herein, both individually and taken in combination.

4. Circuit According to FIG.4

FIG.4shows a block schematic diagram of another circuit400for calibrating a plurality of ATE channels, according to embodiments of the present invention. The circuit400comprises a plurality of ATE channels420,430,440,450and a central measurement unit460. The circuit400comprises some similarities when compared to the circuits200and300. For example, circuit400can comprise a first ATE channel420, a second ATE channel430, a third ATE channel440and a fourth ATE channel450. Moreover, the circuit400comprises a central measurement unit460. However, rather than having two connection networks370,380, circuit400only comprises a single connection network475, which is coupled between a central measurement port462of the central measurement unit460and the ATE channels.

The first ATE channel420is somewhat different from the first ATE channel220and from the first ATE channel320. In particular, the first ATE channel420comprises a series connection of a first diode428aand of a second diode428b. The series connection is similar to the series connection of diodes328aand328b, and also similar to the series connection of diodes228aand228b. Moreover, optionally, there is a switch429a(first switch), which is circuited in parallel to the second diode428band which allows to short circuit the second diode428b. Moreover, there is also a second series connection of a third diode428cand of a fourth diode428dand a switch429bwhich allows to short circuit the third diode428C.

The first series connection of diodes428a,428bis circuited between the DUT connection421and the positive supply voltage (or positive supply voltage rail) (e.g., positive supply voltage VCC). The second series connection of diodes428c,428dis circuited between the negative supply voltage or a negative supply voltage rail and the DUT connection421. Orientations of the diodes can, for example, be seen inFIG.4. Moreover, there is also, optionally, a second switch429b, which is configured to selectively short circuit the third diode428c. it should be noted that the series connection of diodes428a,428bcorresponds to the series connection diodes228a,228b, and that the series connection of diodes428c,428dcorresponds to the series connection of diodes228c,228d. Similarly, the series connection of diodes428a,428bcorresponds to the series connection of diodes328a,328b, and the series connection of diodes428c,428dcorresponds to the series connections of diodes328c,328d. Moreover, it should be noted that the switches429a,429bcorrespond to switches329a,329b. Thus, regarding the functionality of the series connections and regarding the functionality of the switches329a,329b, reference is made to the above description which also applies to the circuit400.

However, the common connection network475is not directly connected to taps within the series connections of diodes. Rather, the common connection network475is coupled to a tap of the first series connection, e.g., between didoes428aand428b, via a first coupling switch427a. Likewise, the common connection network is coupled to a tap of the second series connection, (e.g., between the third diode428cand the fourth diode428d) via a second coupling switch427b. Accordingly, the common connection network475can selectively be coupled to the tap of the first series connection of diodes or to the tap of the second series connection of diodes.

Moreover, the structure of the other ATE channels430,440,450may be equal to the structure of the first ATE channel420. For example, diodes438a,438b,438c,438dmay correspond to diodes428a,428b,428c,428d. Similarly, diodes448a,448b,448c,448dmay correspond to diodes428a,428b,428c,428d. Moreover, diodes458a,458b,458c,458dmay correspond to diodes428a,428b,428c,428d. Moreover, switches439a,439b, corresponds to switches429a,429b, and switches449aand449bcorresponds to switches429aand429b, and switches459aand459bcorrespond to switches429aand429b. Switches437a,437bcorrespond to switches427a,427b. Moreover, switches447a,447bcorrespond to switches427a,427b. Moreover, switches457a,457bcorrespond to switches427a,427b.

For example, the switches427a,427b,437a,437b,447a,447b,457a,457bmay be part of the respective ATE channels,420,430,440,450. For example, the switches427a,427b,437a,437b,447a,447b,457a,457bmay be integrated on chip switches which are integrated on one or more chips that are part of the ATE channels420,430,440,450, and said switches may, for example, be implemented using transistors like, for example, field effect transistors.

Moreover, it should be noted that the switches may, for example, decide which one of the ATE channels is coupled to the central measurement unit460.

In an example, switches427a,437a,447a,457amay be switched together, for example, on the basis of a single common control signal. For example, when switches427a,437a,447a,457aare activated (e.g., in a conductive state), this may allow for a current flow from one of the ATE channels420,430,440,450to the central measurement unit460. In this case, the “other” switches427b,437b,447b,457bshould be deactivated.

On the other hand, if the switches427b,437b,447b,457bare activated, this allows for a current flow from the central measurement unit460to a selected ATE channel (e.g., one of the ATE channels420,430,440,450). In this case, the “other” switches427a,437a,447a,457ashould be deactivated.

For example, a decision regarding which of the ATE channels is the selected ATE channel may, for example, be determined based on the basis of the biasing conditions of the diodes. To select a single ATE channel as a selected ATE channel, which is to be calibrated, the biasing condition of the ATE channels and also the biasing condition provided on the common connection network475should be adjusted to have a single one of the diodes (for example, a single one of the diodes428a,438a,448a,458a) in a conductive state, while the other ones of said diodes should be in a non-conductive state. Alternatively, the biasing should be adjusted to bring a single one of the diodes428d,438d,448d,458dinto a conductive state, while the other diodes are in a non-conductive state. Regarding an adjustment of the biasing, reference is made, for example, to the above description with respect to the circuits ofFIGS.2and3.

Alternatively, a setting of the coupling switches427a,427b,437a,437b,447a,447b,457a,457bmay also be used to decide which one of the ATE channels is selected for a calibration. For example, only a single one or both of the coupling switches inside of one ATE channel may be activated, to thereby uniquely decide which of the ATE channels is selected for calibration.

To conclude, the circuit400according toFIG.4provides for different possibilities to select one of the ATE channels420,430,440,450for a calibration. Both the coupling switches427a,427b,437a,437b,447a,447b,457a,457band the diodes428a,428d,438a,438d,448a,448d,458a,458dcan be used for selecting which one of the ATE channels should be calibrated, e.g., which one of the ATE channels should be effectively coupled to the central measurement port462of the central measurement unit460.

Moreover, it should be noted that the circuit400according toFIG.4may optionally be supplemented by any of the features, functionalities and details described herein, both individually and taken in combination. Moreover, it should be noted that any of the features, functionalities and details of the circuit400may optionally be introduced into any of the other circuits disclosed herein, both individually and taken in combination.

5. Circuit According to FIG.5

FIG.5shows a block schematic of a current measurement circuit, which can be used in the central measurement units130,260,360,460disclosed herein, according to embodiments of the present invention. The current measurement circuit500comprises a current input510which may, for example, be coupled to the central measurement port130,262,362,462described herein. The current measurement circuit may also comprise a voltage generator, a plurality of current measurement resistors, a bias switch, a voltage comparator and a measurement switch. The voltage generator can include a digital-to-analog converter520, an output voltage of which may be programmable on the basis of a digital input information. The voltage generator may (optionally) comprise an associated output buffer522, which may be configured to stabilize an output voltage provided by the digital-to-analog converter520. An output of the buffer522may, for example, be coupled to the bias switch524, which may be configured to couple the output of the buffer522to the plurality of current measurement resistors (e.g., shunt resistors)526a,526b,526c,526d. For example, the bias switch may be configured to selectively (or selectably) couple the output of the buffer522to a first terminal of a first current measurement resistor526aor to a first terminal of a second current measurement resistor526b. There may also be additional current measurement resistors, and the bias switch may also be configured to selectively couple the output of the buffer522to first terminals of said further current measurement resistors526c,526d. Second terminals of the current measurement resistors526a,526b,526c,526dmay, for example, be coupled to the current input510. Thus, the output of the buffer522may selectively (or selectably) be coupled to the current input510via one of the current measurement resistors526a,526b,526c,526d. Moreover, the voltage measurement unit can include an analog-to-digital converter530, which is configured to measure a voltage drop across a currently selected current measurement resistor, which is, for example, selected by the bias switch524. For this purpose, the current measurement circuit500may be configured to determine a voltage drop across the selected current measurement resistor. The voltage measurement unit may (optionally) include a differential amplifier540for sensing an analog voltage across the selected current measurement resistor. For example, a first input (e.g., a non-inverting input) of a differential amplifier540may be coupled to the current input510, and a second input of the differential amplifier (for example, an inverting input) may be selectively coupled to a first terminal of the selected current measurement resistor. For example, a measurement switch544may be used to selectively couple the inverting input of the differential amplifier540to a first terminal of a selected current measurement resistor (e.g., out of the current measurement resistors526ato526d). Thus, the inverting input of differential amplifier540may, for example, be coupled to the first terminal of the same current measurement resistor which is currently coupled to the output of the buffer522via the bias switch524. The bias and measurement switches524and544may, for example, be coordinated. Moreover, an output voltage provided by the differential amplifier540may, for example, be input into an analog-to-digital converter530, which may therefore obtain an information about a voltage drop across the currently selected current measurement resistor.

To conclude, the current measurement circuit500may, for example, adjust a potential at the current input510. For example, the potential at the current input510may be substantially identical to the potential at the output of the buffer522, wherein it can be assumed that the voltage drop across the respective (currently selected) current measurement resistor526a,526b,526c,526dis comparatively small (since current measurement resistors are, for example, chosen to have a sufficiently small voltage drop across them). However, it should be noted that, in some embodiments, the voltage across a current measurement resistor should not be very small, because a small voltage usually results in a large noise. The normal voltage drop heavily depends on the real application. In this case of ATE calibration, for example, bigger voltages (e.g., 0.5V-1V) can be utilized.

Consequently, it is possible to adjust the potential (or voltage) at the current input510with good accuracy by providing an appropriate digital input information to the digital-to-analog converter520. Moreover, the current flow through the current input510generates a voltage across the currently selected current measurement resistor, wherein the voltage drop is substantially proportional to the current. Accordingly, it is possible to adjust the potential (or a voltage) at the current input while accurately measuring the current flowing through the current input. Thus, the current measurement circuit500allows for the above-mentioned adjustment of the potential (or voltage) on the one or more connection networks (e.g., on the first connection network and on the second connection network, or on the common connection network). Consequently, the current measurement circuit can be utilized to apply an appropriate bias, which, in turn, puts one of the diodes into a forward bias (when used in combination with an appropriate setup of potentials provided at the DUT connections of the ATE channels). Therefore, the current measurement circuit500is well-usable in embodiments according to the present invention.

6. Conclusions and Further Embodiments

Embodiments according to the present invention advantageously provide for improved current calibration for ATE channels. Channel pin electronics (PE), also designated with ATE PE, normally are comprised of a driver, a comparator, an active load and a parametric measurement unit (PMU unit or PM unit). The latter two, for example, the active load and the parametric measurement unit, have current force capability, and the parametric measurement unit (PMU unit or PM unit) also has current measurement capability.

However, it should be noted that it is not necessary that an ATE channel has all of the above-mentioned functionalities. For example, it may be sufficient that an ATE channel comprises a comparator and a parametric measurement unit. In other cases, it may also be sufficient that an ATE channel comprises a driver and a parametric measurement unit. In other embodiments, it may also be sufficient that an ATE channel has an active load and a parametric measurement unit. In some specific samples, it may even be sufficient that an ATE channel comprises one of the above-mentioned components (driver, comparator, active load, parametric measurement unit).

In order to be able to calibrate the force and/or measure currents (for example, the currents forced by the driver and/or by the active load and/or by the parametric measurement unit and/or the current measured by the parametric measurement unit), a central measurement unit (CMU) with precise current measurement capabilities (and/or current sourcing capability and/or current sinking capability) accesses the channels. For example, in conventional solutions, this access is usually done via an individual relay per channel. However, it has been found that these relays consume precious board space limiting the number of channels on a given area. Also, it has been found that the relays (when open) have a significant capacitance which dramatically limits the frequency of the signals between the pin electronics and the device under test.

Embodiments according to the invention show an improved architecture where the individual relays can be avoided for current calibration.

In some embodiments according to the invention, just one relay and the central measurement unit (CMU) is used (or needed).

According to an aspect of the invention, the normally available ESD (electrostatic discharge) diode circuit is extended and, optionally, simple on-chip switches are added.

According to an aspect of the invention, two additional pads are needed per chip in some implementations. For example, if each of the ATE channels220,230,240,250is implemented on an individual chip, two additional pins or pads are needed per chip, for example, for connecting to the first connection network and the second connection network.

In a normal operation, the switches (e.g., the switches329a,329b,339a,339b,349a,349b,359a,359bor the switches429a,429b,439a,439b,449a,449b,459a,459b) are closed. For example, in normal operation the switches are closed so that the diodes328a,dserve as ESD-Diodes which is better than the series combination of328a+b,329c+das ESD protection.

In calibration mode, (at least) the switches of the to-be-calibrated channel (e.g., at least one of the switches329a,329b, if the first ATE channel320to be calibrated) is opened.

In some embodiments, the relay at the central measurement unit (CMU) (e.g., the relay290or the relay390) selects either one or the other line (e.g., either the first connection network270or the second connection network280) depending on the sign (or current direction) of the to-be-calibrated current.

In some embodiments, a minor drawback is the fact that the voltage, at which the currents can be calibrated, is smaller (or larger, depending on the direction of the current) than in conventional solutions, due to the diodes' forward voltage. However, it has been found that this is not a serious problem in most cases.

Another embodiment according to the invention (e.g., as shown inFIG.4) adds additional switches on the chip (e.g., switches427a,427b,437a,437b,447a,447b,457a,457b) so that only one pad (or pin) per chip is needed, and the relay at the central measurement unit (e.g., at the central measurement unit460) can also be avoided.

Preferably, the additional on-chip switches (e.g., the switches427a,427b,437a,437b,447a,447b,457a,457b) may to be able to carry the maximum current.

According to an aspect, leakage currents may be minimized here because the number of diodes “sitting on the dc-cal bus” is very limited (wherein this cal bus, for example, effectively is node475).

An appropriate CMU current measure implementation with floating termination of precision resistors (e.g., multiples, switched because of various current ranges) is also shown (for example, inFIG.5). Floating termination, via a digital-to-analog converter (e.g., via the digital-to-analog converter520) is used (or in some cases even needed) to correctly calibrate voltage-dependent ATE-PE currents with the analog-to-digital converter (e.g., the analog-to-digital converter530).

As an additional remark, it should be noted that there are, for example, three options, e.g., as shown inFIGS.2,3and4. It has been found that an option without internal switches (e.g., as shown inFIG.2) can also do the job. This can be the case if two diodes in series can effectively be used as for ESD protection. All three options are part of the invention.

Accordingly, embodiments according to the invention create a concept for an improved current calibration, which can be used in automated test equipment. For example, it is possible to reduce the costs of the LTE and to increase the pin count of the LTE using concepts disclosed herein.