Apparatus and method for monitoring a state, in particular of a fuse

The present invention provides an apparatus for monitoring a state, in particular of a fuse (4), having: a first state storage device (11) for storing a state, in particular of a fuse (4); a second state storage device (12) for storing the state of the first state storage device (11); and a logic device (9) for comparing the states of the two state stores (11, 12); the first state store (11) being able to be driven for renewed reading in of the state, in particular of the fuse (4), in the event of a noncorrespondence of the states in the two stores (11, 12). The present invention likewise provides a method for monitoring a state, in particular of a fuse.

TECHNICAL FIELD

The present invention relates to an apparatus and a method for monitoring a state, in particular of a fuse.

BACKGROUND ART

Latching fuse state storage circuits (fuse latch circuits) are used to store apparatus-relevant information, such as e.g. the state of a fuse, or repair information for memory chips. Latching fuse state stores (fuse latches) are exposed to the influence of errors that can be rectified, to a disturbance mechanism which is caused by particles, in particular α particles, which penetrate through the active state storage area and alter the state of the state store.

This represents a serious problem since the apparatus may be in operation for an indeterminate length of time and the error (incorrect stored state of the fuse to be monitored) is not corrected since the state stores (latches) are only set during the run-up or during the start of the apparatus. Module-relevant information, such as the repair information, is lost and cannot be recovered while the apparatus is active. Even more important is the fact that errors which [lacuna] by such state stores (latches) that have changed over unintentionally are difficult to detect. In present-day designs, the setting of the state store (set a fuse latch) is a “global” operation, which means that all the state stores (fuse latches) are set simultaneously. Therefore, it is not possible to refresh the state store information while the apparatus is active.

The problem has been alleviated hitherto by derating a state storage circuit (fuse latch circuit). This reduces the probability of an error occurring, but ultimately does not solve the problem.

FIG. 1illustrates a customary state storage circuit. A supply voltage1(VDD) is connected via a first switching device23, in particular a field-effect transistor, to an actual state store3(fuse latch), which has two inverters I. The first switching device23is actuated by a first drive signal5(FPUP). Via a connection16, the first switching device23is connected to a second switching device24, which is actuated by a second drive signal6(FPUN). Located between the second switching device24and a ground terminal2is the fuse4whose state is monitored by the circuit in accordance withFIG. 1. In parallel with the connection16between the first switching device23and the second switching device24, the two inverters I are connected in series, between the two inverters a signal branching off to a detection device15, in particular a decoding device.

FIG. 2shows the drive signals5,6plotted against time in order to elucidate the method of operation of the arrangement according toFIG. 1. The drive signal5(FPUP), which is applied to the first switching device23, controls the resetting (reset) of the state store3. After the run-up, a low level signal at the switching device23effects a resetting7(reset) of the state store3(latch). The second drive signal6(FPUN) controls the setting (set) of the state store3(latch), in which case, in the event of a high level signal at the second switching device24, the state store3(latch) is set8(set latch) in accordance with the state of the fuse4, which may be intact or blown. This operation is effected only once in each case after the activation of the apparatus during the run-up sequence in the event of a start-up.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an apparatus and a method for monitoring the state of a fuse which identifies, and in particular corrects, state storage devices (fuse latch) that have switched over unintentionally, without impeding the operation of the apparatus during the monitoring process.

According to the invention, this object is achieved by means of the apparatus specified in claim 1 and by means of the method according to claim 8.

The idea underlying the present invention consists in providing a second state storage device (e.g. fuse latch) and a state comparison/control logic.

In the present invention, the problem mentioned in the introduction is solved in particular by the states of two state storage devices (e.g. fuse latches) being compared in a comparison/control logic and, in the event of a noncorrespondence of the two states, a renewed checking of the state, e.g. of the fuse, being carried out with subsequent copying of the state acquired in the first state storage device into the second state storage device.

Advantageous developments and improvements of the respective subject matter of the invention are found in the subclaims.

In accordance with one preferred development, the first state store can be driven for reading in the state, in particular of the fuse, by the logic device.

In accordance with a further preferred development, the apparatus has a switching device, which can be driven by a copying signal for copying the state stored in the first storage device into the second storage device by the logic device.

In accordance with a further preferred development, the logic device can generate an error signal for indicating the noncorrespondence of the two states in the two storage devices.

In accordance with a further preferred development, the second state store is connected to one or more decoding devices.

In accordance with a further preferred development, the apparatus is used in a semiconductor memory device.

DETAILED DESCRIPTION OF THE INVENTION

In the figures, identical reference symbols designate identical or functionally identical constituent parts.

FIG. 3shows the block diagram of an apparatus for monitoring the state of a fuse for elucidating an embodiment of the present invention.

FIG. 3illustrates a first state storage device11, which is connected to a ground terminal2(GND) via a fuse4. A first drive signal5(FPUP) and a second drive signal6(FPUN) are applied to the first state storage device11. Via a connection21, the first state storage device11is connected to a logic device9, which performs in particular comparison and control tasks (compare/control logic). A second state storage device12is likewise connected to the logic device9via a connection22.

Located between the first state storage device11and the second state storage device12is a switching device14, which is actuated according to the logic device9. The first state storage device11(first fuse latch) essentially corresponds to the customary state storage device explained with reference toFIG. 1and is used to detect the state of the fuse4. However, instead of being connected directly to a decoding device15or a decoding circuit, as shown inFIG. 1, the first state storage device11can be connected to the second state storage device according to the switching device14, the second state storage device (second fuse latch) being connected to the decoding device15.

The switching device14allows the copying of the state stored in the first state storage device11into the second state storage device12. The logic device9compares, in particular permanently, the contents of the two state storage devices11,12and, in the case of a detected noncorrespondence of the two states in the state storage devices11,12, can cause, via the connections25,26, which, in particular, transmit signals whose signal waveform corresponds to that of the first and/or second drive signal5,6, the first state storage device11to check the state of the fuse4anew and to forward the newly generated storage content of the first state store11via the switching device14to the second state storage device12according to a copying signal10, which issues from the logic device9to the switching device14.

An error signal13(error) can be communicated to other circuit sections or systems (not illustrated) by the logic device9. Such a disturbance, in particular the noncorrespondence of the two states which are stored in the two state storage devices11,12, occur [sic] as a result of the impinging of particles on the state storage areas, in particular as a result of the impinging of α particles.

According to the present invention, the state of the first state storage device11can be adjusted anew with the state of the fuse4to be monitored, without being superimposed with the operation of the apparatus, and can consequently serve as a reference. In the case of a detected noncorrespondence of the states of the two state storage devices11,12, it is initially not known whether the first or second state storage device10or11has an item of information that is corrupted, in particular by an α particle.

The detection of a noncorrespondence initiates a renewed checking of the state of the fuse4and a renewed storage of said state in the first state storage device11, which is followed by a process of copying to the second state storage device12. This process can take place locally and only for the state storage devices11,12(fuse latches) which exhibit a noncorrespondence. This local process is advantageous since it reduces the influence of the state store update on the operation of the apparatus.

Such state storage devices are employed in particular in semiconductor memory devices.

Although the present invention has been described above essentially on the basis of a preferred exemplary embodiment, it is not restricted thereto, but rather can be modified in diverse ways.

Thus, e.g. the connections16,25,26,21,22between the individual apparatus units, such as, for example, the logic device9and a state storage device11,12, are not only conceivable as an electrical line but can also be realized optically.

Moreover, the invention is not restricted to the application possibilities mentioned (fuse latch stores or logic circuits), but rather can be applied to any desired circuits.