Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With storage means for voltage or current
Reexamination Certificate
1999-09-22
2001-11-20
Nguyen, Vinh P. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With storage means for voltage or current
Reexamination Certificate
active
06320368
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a method for determining the driver capability of a driver circuit of an integrated circuit.
Driver capability is understood here in what follows as the capability of the driver to supply a specific current within a specific period of time. A possible way of determining the driver capability of a driver circuit is to use a current measuring device to measure the current driven by it. However, current measuring devices require a relatively high degree of expenditure on hardware.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for determining the drive capability of a driver circuit of an integrated circuit, which overcomes the above-mentioned disadvantages of the prior art methods of this general type, which can be implemented with little hardware expenditure, for determining the driver capability of a driver circuit of an integrated circuit.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for determining a drive capability of a driver circuit of an integrated circuit, which includes: deactivating the driver circuit and placing a capacitor disposed at an output of the driver circuit at a first potential; activating the driver circuit at a first point in time so that current flows between the output and the capacitor; interrupting the current flowing between the output of the driver circuit and the capacitor at a second point in time; and determining subsequently a potential at the capacitor as a measure of the drive capability of the driver circuit.
The method according to the invention provides that, when a driver circuit is deactivated, a first capacitor at the output of the driver circuit is placed at a first potential. The driver circuit is activated at a first point in time, so that a current flows between its output and the first capacitor, but the flow of current between the output of the driver circuit and the first capacitor is interrupted at a second point in time and that the potential at the first capacitor is subsequently determined as a measure of the driver capability of the driver circuit.
Instead of the direct measurement of the current that has flowed from the driver circuit between the first and second point in time, in the invention the potential at the first capacitor is determined. Since the potential has been placed at the known, first potential before the first point in time, the difference between the potentials at the first capacitor after the second and before the first point in time is proportional to the charge which has flowed, and thus to the current which has flowed. This results from the equation Q=C*U given a capacitance which is assumed to be constant, and from
C
=
ⅆ
Q
ⅆ
t
=
C
*
ⅆ
U
ⅆ
t
.
Here, the change in charge dQ is proportional to the current that has flowed. Since the first capacitance is assumed to be known, and the period of time between the first and the second points in time is also known, it is therefore possible to determine the driver capability of the driver circuit by determining the potential after the second point in time at the first capacitor.
According to one development of the invention, the potential of the first capacitor is determined by an evaluation unit connected to it. Therefore, the driver capability is determined by components that are located on the integrated circuit, so that an external testing device is not required for this. The internal evaluation unit of the integrated circuit can subsequently supply, for example, a corresponding result signal to outside the integrated circuit, the signal indicating whether the driver capability that has been determined exceeds or drops below a previously defined limiting value. According to one development, the driver circuit has a first switching element that is disposed in a main current path, connected to it at the output, of the driver circuit and which has a first, relatively long switching time, and the output of the driver circuit is connected to the first capacitor via a second switching element which has a second switching time which is relatively short in comparison with the first switching time.
Here, the second switching element is energized at the latest at the first point in time and is switched off precisely at the second point in time, so that the flow of current between the output of the driver circuit and the first capacitor is interrupted. Here, “switching time” is understood to be the time within which the switching element is completely switched off starting from the conductive state by an appropriate control signal.
Since the first switching element is disposed in the main current path of the driver circuit, its slow switching behavior decisively influences the switching behavior of the driver circuit. Using the comparatively quickly switching, second switching element ensures that the flow of current between the output of the driver circuit and the first capacitor is interrupted relatively quickly as a result of the second switching element switching off at the second point in time. If, on the other hand, it was desired to interrupt the flow of current by switching off the first switching element, its slow switching behavior would only result in the first switching element being switched off with a delay relative to the latter, after a corresponding control signal has assumed a deactivated level. The first and second switching elements may, for example, be transistors to whose control terminals appropriate control signals can be applied. A transistor with a relatively long switching time is obtained if the width to length ratio of its main current path assumes a high value. Conversely, a relatively short switching time is obtained if the width to length ratio of a transistor assumes a relatively small value. Using the second switching element makes it possible to interrupt the flow of current between the output of the driver circuit and the first capacitor even if the first switching element and thus the driver circuit are still driving a current.
According to one development, the first capacitor is connected to a second capacitor via a third switching element. The third switching element is switched off at the latest at the first point in time and is energized at a third point in time that occurs after the second point in time. The potential of the first capacitor is determined a first time before the third point in time and a second time after the third point in time as a measure of the driver capability of the driver circuit.
In this way, it is possible to determine both before and after the third point in time whether the potential at the first capacitor exceeds or drops below a predefined limiting value. Since, after the third point in time, the second capacitor is disposed parallel with the first capacitor, a capacitive voltage divider is obtained, as a result of which charge flows from the first capacitor to the second capacitor, or vice-versa. As a result, the potential of the first capacitor changes and it is also possible subsequently to determine on which side of the predefined limiting value it lies. With further, corresponding switching elements, it is possible to switch further capacitors in parallel with the first and second capacitors at later points in time. After each further capacitor has been connected into the circuit, it is then possible to determine again the potential at the first capacitor and a comparison can be made with the predefined limiting value. In the manner described it is possible to determine the driver capability of the driver circuit relatively precisely although only a single evaluation unit or comparison circuit with a single permanently set reference value is required for the respective comparison of the potential of the first capacitor with a predefined limiting value.
According to one development, a load which is connected to the output of the driver circuit is activated between the first and second points in ti
Schamberger Florian
Schneider Helmut
Greenberg Laurence A.
Lerner Herbert L.
Nguyen Vinh P.
Siemens Aktiengesellschaft
Stemer Werner H.
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