Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2002-09-13
2004-06-29
Le, N. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S763010, C324S765010, C324S1540PB
Reexamination Certificate
active
06756787
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to an integrated circuit having circuits that will be tested by an external test system, and to an external test system.
As a result of increasing complexity, testing integrated circuits is becoming more and more time-consuming. This leads to higher costs, and as a rule, reduces the throughput in the fabrication of integrated circuits. In order to reduce the test costs or to increase the throughput, it is necessary, for example, to increase the parallelism during testing. One further possibility is to reduce the requirements placed on the external test systems, in order in this way to reduce the test duration and therefore the costs.
For instance, a self-test (BIST=build-in self-test) is performed, during which the integrated circuits are tested by suitable additional circuits that are actually configured on the integrated circuit that will be tested.
Integrated circuits can exhibit an increased current consumption because of defects such as short circuits or within the context of process fluctuations in fabrication. In order to identify corresponding chips, it is necessary to measure a current flow through the entire integrated circuit or parts thereof during the production test. This current measurement has hitherto been carried out by a DC measurement unit. For this purpose, an appropriately equipped external test system is required which, during the parallel testing, needs a separate measuring unit for each of the integrated circuits that will be tested.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an integrated circuit in which the current consumption can be measured more quickly during testing and in which lower requirements are placed on the external test system. It is furthermore an object of the present invention to provide a method for measuring current in such an integrated circuit.
With the foregoing and other objects in view there is provided, in accordance with the invention, an integrated circuit, including: a circuit having a current flowing therein; an external connection; and a current measuring unit for obtaining a measured current representing the current flowing in the circuit. The current measuring unit includes an output device for outputting a value of the measured current to an external test system via the external connection. The current measuring unit includes a measurement current path. The current measuring unit includes a current measuring circuit. The current measuring unit includes a current mirror circuit for obtaining a mirrored current by mirroring the current flowing in the circuit into the measurement current path. The measurement current path is led through the current measuring circuit so that the measured current can be obtained by measuring the mirrored current and so that the value of the measured current can be output by the output device. The current measuring circuit includes a capacitor. The current measuring circuit includes a switching device for charging the capacitor from a low voltage value to a high voltage value by using the mirrored current and for reversing a polarity of the capacitor when a voltage value stored in the capacitor exceeds the high voltage value. A number of charging operations of the capacitor occurring during a predetermined time period depend in an unambiguous way on the mirrored current.
In accordance with an added feature of the invention, the current measuring circuit has a counter device designed to measure the number of the charging operations of the capacitor occurring during the predefined time period; and the counter device outputs the number of the charging operations via the output device.
In accordance with an additional feature of the invention, there is provided, a second current measuring circuit including a second switching device, a second capacitor, and a second counter device. The second current measuring circuit obtains a predetermined current. The second capacitor is charged by the predetermined current for a predetermined number of recharging operations of the second capacitor. The second counter device is connected to the first current measuring circuit for starting the first counter device to begin counting the predetermined number of charging operations of the second capacitor and for stopping the first counter device after the predetermined number of recharging operations of the second capacitor has been reached.
In accordance with another feature of the invention, the output device is configured to serially transmit the value of the measured current to the external test system.
In accordance with a further feature of the invention, the integrated circuit includes a DRAM memory circuit.
In accordance with a further added feature of the invention, the current measuring circuit has a capacitor that can substantially be charged up via the mirrored current.
In accordance with another added feature of the invention, the output device is configured to output the measured value as a digital value.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of measuring a current in a circuit in an integrated circuit. The method includes steps of: providing the integrated circuit with a current measuring unit including a current mirror circuit for mirroring the current in the circuit into a measurement current path; providing the current measuring unit with an output unit to output a measured value of a measured current via an external connection; providing a voltage to the integrated circuit which lies a predetermined amount above a nominal supply voltage of the integrated circuit, the predetermined amount corresponding to a voltage drop across a transistor in the integrated circuit; and obtaining the measured value in dependence on a current consumption of the circuit.
In accordance with an added mode of the invention, the method includes steps of: outputting a reference current to the integrated circuit; and determining the measured value by using the reference current and outputting the measured value with the output device.
According to the invention, an integrated circuit is provided with a circuit that has a current measuring unit. The current measuring unit is used to measure the current through the circuit, and the current measuring unit is connected to an output device. The output device is configured in such a way that the value of the measured current can be output to an external test system via an external connection of the integrated circuit.
According to the invention, therefore, the current measuring unit is provided within the integrated circuit instead of, as had customarily been the case, providing the current measuring unit outside the integrated circuit, for example, in the external test system or connected to the external test system. In this way, the current through the circuits of the integrated circuit can be measured at any time, so that during the parallel testing of a plurality of integrated circuits, the current through the circuits of each of the integrated circuits can be measured substantially simultaneously in each case and can subsequently be transmitted to an external test system, for example. This therefore avoids the necessity of providing an additional current measuring unit outside the integrated circuit, in which the current measurements would have to be carried out sequentially if a sufficient number of external current measuring devices are not available.
Since it is frequently customary to provide integrated circuits with a BIST circuit, a data output used by the BIST circuit can also be used to output the current value.
A further advantage resides in the fact that, during the current measurement, a common voltage source can be used for a plurality of integrated circuits that will be tested in parallel. Individual voltage sources for an external current measuring unit in each case are therefore not necessary.
Provision can preferably be made for the output device to be configured to tra
Beer Peter
Ohlhoff Carsten
Greenberg Laurence A.
Infineon - Technologies AG
Le N.
Mayback Gregory L.
Nguyen Vincent Q.
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