Decoder Circuit

1. Field of the Invention

The present invention relates to a decoder circuit for a storage module having storage cells constructed from MOS transistors which are arranged between word and bit lines, and more particularly to such a decoder circuit in which, for the selection of one of the word lines or bit lines, the control inputs of the decoder transistors are fed with n address signals in negated or non-negated form and a decoder output signal is emitted on a decoder output line which connects terminals of the controlled paths of the decoder transistors.

2. Description of the Prior Art

Decoder circuits for storage modules in which the storage cells consist of MOS transistors are arranged between word lines and bit lines as is known, for example, from the IBM Technical Disclosure Bulletin, Vol. 12, No. 13, May 1970, Page 2082. In this publication, a decoder circuit is provided for each bit line and word line. The decoder circuit consists of MOS transistors whose control paths are arranged parallel to one another. In the following, these MOS transistors will be referred to as decoder transistors. The control inputs of these decoder transistors are fed with address signals in non-negated form or in negated form. The one electrodes of the controlled paths of the decoder transistors are connected to one another and form a so-called decoder output line, which generally is connected to an output amplifier which leads to the bit line and word line of the storage module. The other electrodes of the controlled paths of the decoder transistors are likewise connected to one another and then connected to an operating voltage. The mode of operation of such a known decoder circuit is well known in the art and will not be discussed further hereinbelow.

Conventionally, the decoder circuits are integrated, together with the storage cells of a storage module. Therefore, a problem exists in designing the decoder circuits so that they assume a space on the storage module which is as small as possible. To this end, it is known to arrange the decoder transistors on the semiconductor module in parallel to the address lines, whereas the decoder output lines and the lines for the operating voltage are arranged at right angles to the address lines. In this case, the address lines are metal lines, whereas the decoder output lines and the line for the operating voltage are diffused into the semiconductor module. A disadvantage of such an arrangement resides in the fact that the decoder grid formed from the decoder output line to the line for the operating voltage is relatively large.

It is also known to arrange the decoder transistors in parallel to the decoder output lines, whereas the address lines are arranged at right angles to the decoder output lines. In this case, two address lines are, in each case, followed by a line for the operating voltage. Here, the address lines are in the form of silicon address lines. In this embodiment, the decoder grid is smaller than in the previously described situation, although the height of the decoder circuit, which corresponds approximately to the length of the decoder output line, is larger.

The object of the present invention resides in the provision of a decoder circuit which is designed in such a manner that its integration onto a semiconductor module requires less space than known decoder circuits.

The above object is realized according to the present invention, for a decoder circuit of the type generally described above wherein n-1 decoder transistors are arranged with their controlled paths in parallel and a further decoder transistor is provided whose control input is supplied with an address signal in negated form and whose controlled path is arranged between a connection line which connects the one ends of the controlled path of the n-1 decoder transistors and an operating voltage. An additional decoder transistor is provided whose control input is fed with the address signal in nonnegated form and whose controlled path is connected between the operating voltage and a second connection line which connects the other ends of the controlled paths of the decoder transistors. Furthermore, the first and second connection lines form respective decoder output lines for the selection of a word line or a bit line.

If the number of the address signal with which a decoder circuit must be operated is referred to n, where n is an integer, n-1 decoder transistors are arranged in parallel to one another. This is to say that the controlled paths of these decoder transistors are each connected to one another by a first and a second connection line. A further decoder transistor is provided, whose controlled path lies between an operating voltage and the first connection line of the n-1 decoder transistors. This further decoder transistor is operated by an address signal in negated form. Finally, as set forth above, an additional decoder transistor is provided which lies between the second connection line of the n-1 decoder transistors and the operating voltage. This additional decoder transistor is operated by the address signal in non-negated form. The first and the second connection lines of the decoder circuit each form a decoder output line, each of which can, for example, be connected to an output amplifier which leads to a word line or a bit line.

A decoder circuit constructed along the line set forth above can be integrated on a semiconductor module in such a manner that the n-1 decoder transistors lie parallel to the address lines. On the other hand, the further decoder transistor and the additional decoder transistor are arranged in parallel to the decoder output lines. The line for the operating voltage is required only once and can be located at the edge of the decoder circuit on the storage module. Thus, no internal line is required for the operating voltage within the decoder circuit. The result of this construction is a very small decoder grid, which corresponds approximately to the decoder grid which exists in the known decoder circuit with the silicon address lines, although the decoder circuit of the present invention has a considerably smaller height than the previously known decoder circuit.

A further advantage of the decoder circuit constructed in accordance with the present invention consists in that the address lines can be constructed with metal. This has the advantage of short signal transit times on the address lines. Another and essential advantage consists in that the number of decoder transistors per address line is considerably reduced.

Other objects, features and advantages of the invention, its organization, construction and operation will be best understood from the following detailed description taken in conjunction with the accompanying drawings on which:

FIG. 1 is a schematic illustration of a known decoder circuit in which the decoder transistors are arranged in parallel to the address lines;

FIG. 2 is a schematic illustration of a known decoder circuit in which the decoder transistors are arranged in parallel to the decoder output lines;

FIG. 3 is a schematic illustration of a decoder circuit constructed in accordance with the present invention;

FIG. 4 is a pulse chart for the decoder circuit of the present invention corresponding to FIG. 3, in which the voltages are plotted with respect to time;

FIG. 5 is a schematic illustration of a decoder circuit constructed in accordance with the invention on the storage module;

FIG. 6 is a schematic illustration of decoder circuits corresponding to FIG. 1;

FIG. 7 is a schematic illustration of the decoder circuits corresponding to FIG. 2; and

FIG. 8 is a schematic illustration of decoder circuits constructed in accordance with FIG. 5.

Referring to FIG. 1, a known decoder circuit on a storage module is schematically illustrated. In this known decoder circuit, the decoder transistors DT are arranged in parallel to a plurality of address lines A. The controlled paths of the decoder transistors DT lie between a plurality of decoder output lines D and a line for the operating voltage VSS. The control inputs of the decoder transistors DT are each connected to the address lines A. In this example, the address lines are constructed in metal, whereas the decoder output lines and the line for the operating voltage VSS are diffused into the semiconductor module. It can be seen from FIG. 1 that the decoder grid R, which is required for integrating the decoder transistors DT of the decoder circuit on the storage module, is relatively large. This can also be seen from FIG. 6, in which two decoder circuits DG are arranged next to one another and are connected to an output amplifier AV via a decoder output line Di and Di+1. The output amplifier AV is fed with a selection timing signal WA. Here again, the decoder grid R is relatively large, whereas the height H of the overall decoder circuit with the output amplifier AV is relatively low. The reason for the low height consists in that the decoder transistors DT lie parallel to the address lines, and because of the large decoder grid R the output amplifiers AV can be arranged next to one another.

FIG. 2 illustrates the arrangement of another known decoder circuit on a storage module. Here, the decoder transistors DT lie in parallel to the decoder output lines Di and Di+1. The address lines A are arranged at right angles to the decoder output lines D. Now the decoder output lines D consist of metal, whereas the address lines A consist of silicon. In this embodiment of the decoder circuit, between two address lines is arranged a respective line for the operating voltage VSS which is diffused into the semiconductor substrate.

Since the decoder transistors DT now lie parallel to the decoder output lines D, the decoder grid R is relatively small, although the height H of the decoder circuit on the storage module is relatively great. This can be seen better in FIG. 7. Here again, two decoder circuits DG are arranged next to one another. However, the output amplifiers AV are arranged displaced in relation to one another, as in this case the decoder grid R is too small. The result is that the height H of the overall circuit, consisting of the decoder circuit DG and the output amplifier AV becomes great.

FIG. 3 illustrates a decoder circuit constructed in accordance with the invention. In the event that the decoder circuit is to analyze n address signals, or n is an integer, n-1 decoder transistors are arranged in parallel to one another. This means that their controlled paths lie in parallel to one another and one terminal of the controlled paths are connected to each other by a first connection line L1, whereas the other terminals of the controlled path are connected to each other by a second connection line L2. In the exemplary embodiment the control imputs of these n-1 decoder transistors DT1 to DTn are supplied with the address signals A1 to An in negated or non-negated form. In the exemplary embodiment only two of these decoder transistors are illustrated, these being the decoder transistors DT1 and DTn, and these decoder transistors are fed with the address signal A1 and the address signal An.

A further decoder transistor DTW is provided, whose controlled path is arranged between the first connection line L1 and a line for the operating voltage VSS. The control input of this further decoder transistor DTW is fed with the address signal A0, in negated form A0.

Between the connection line L2 and the connection line for the operating voltage VSS is arranged an additional decoder transistor DTZ whose control imput is fed with the address signal A0 in non-negated form. The connection lines L1 and L2 form decoder output lines Di and Di+1, respectively. These docoder output lines can be connected to the bit/word lines X1 and Xi+1 without the interposition of an output amplifier. In the exemplary embodiment illustrated in FIG. 3, however, an output amplifier AV1 and AV2 is connected between the decoder output line D and the line X.

The construction of the output amplifier AV consists of a precharging transistor VT1, a cut-off transistor AT, a second precharging transistor VT2 and an output stage consisting of a switching transistor SCH and a coupling capacitor C. The pre-charging transistors VT1 and VT2 are fed with a timing signal S before the storage module is to be selected. As a result, the pre-charging transistors VT1 and VT2 are rendered conductive, and the decoder output line D and a point E are charged to a specific potential. During this time the cut-off transistor AT is blocked. To this end, its control input is fed with a voltage VDD - UT. Here, the potential VDD is a further operating voltage, and the potential UT is the threshold voltage of the cut-off transistor. The selection timing signal WA is connected to the output stage, i.e. to the switching transistor SCH. The precise mode of operation of the amplifier is known in the prior art and will not be discussed herein in further detail.

Making reference now to the pulse diagram of FIG. 4, the action of the decoder circuit will be described. Here, it is assumed that the MOS transistors are to be brought into the conductive state by means of high potential.

First of all, the signal S is applied. This signal has a high potential and consequently the pre-charging transistors VT1 and VT2 are driven conductive. The decoder output lines Di and Di+1, and the points Ei and Ei+1 can thus charge to high potential. During this time the decoder transistors DT are not connected with any address signals. The selection timing signal WA also is not connected. The low potential prevails on the lines Xi and Xi+1 which are connected to the bit/word lines.

It will now be assumed that the address signal A0 and the address signals A1, An, are applied. Then, the additional decoder transistor DTZ is rendered conductive, whereas the other decoder transistors DT1, DTn and DTW remain blocked. The result is that the decoder output lines Di+1 can discharge to the operating voltage VSS (VSS being a low potential), whereas the decoder output line Di remains at high potential. As the signal S has previously been disconnected, the pre-charging transistors VT1 and VT2 of the output amplifier AV have passed into the blocked state.

As a result of the potential on the line Di+1, now the cut-off transistor AT of the output amplifier AV2 is driven conductive, and the point Ei+1 can thus discharge to a low potential. On the other hand, the potential at the point Ei remains at its previous value. Therefore, higher potential prevails at the control input of the switching transistor SCH of the output amplifier AV1, whereas low potential prevails at the control input of the switching transistor SCH of the output amplifier AV2. If, now, the selection signal WA is connected, the switching transistor SCH of the output amplifier AV1 can pass into the conductive state, and thus high potential appears on the line Xi. The feedback across the capacitor C serves to speed up this switch through process. Therefore, the line Xi has been selected.

As the point Ei+1 carries low potential, the switching transistor SCH of the output amplifier AV2 cannot be brought into the conductive state, and the potential on the line Xi+1 remains at a low value.

In FIG. 4, the broken lines indicate the case in which the output line X has not been selected, whereas the solid lines indicate the case in which the line X has been selected.

The exemplary embodiment discloses the situation in which the address signal A0 is connected in non-negated and in negated form to the decoder transistors DTW and DTZ. Naturally it is also possible to connect a different pair of address signal instead of these particular signals.

As can be seen from FIG. 3, the decoder circuit, in each case, controls two word or bit lines X. Thus, the same decoder transistors are utilized for the selection either of the one or of the other word or bit line Xi, Xi+1. For this reason, the number of decoder transistors per address line is considerably smaller.

FIG. 5 illustrates how the decoder circuit can be arranged on a semiconductor module. It can be seen that the n-1 decoder transistors are arranged in parallel to the address lines. Now the address lines are designed as metal strips. The additional and the futher decoder transistors, on the other hand, are arranged with the controlled paths in the decoder output lines Di and Di+1, and thus are arranged at right angles to the address lines. The decoder output lines Di and Di+1 are diffused into the semiconductor substrate. Only one line is provided for the operating voltage VSS, which can be arranged at the lower edge of the decoder circuit. This can also consist of metal. As the same n-1 decoder transistors are in each case used for controlling two decoder output lines Di and Di+1, the decoder grid R becomes considerably smaller in relation to FIG. 1. As in addition the n-1 decoder transistors DT lie in parallel to the address lines, the height H is also relatively low, i.e. very much smaller than in the decoder circuit illustrated in FIG. 2. These conditions are shown even better in FIG. 8. The decoder circuit for two decoder output lines Di and Di+1 is referenced DDG. It will be seen that the decoder grid R is very small and that in addition the height H, which is formed by the decoder circuit DDG and the output amplifiers AV, is relatively small. In this case, the output amplifiers must again be arranged displaced from one another. Therefore, the embodiment constructed in accordance with the invention, of the decoder circuit, has considerably reduced the space requirement for the decoder circuit on the storage module.

For example, in the decoder circuit of FIG. 1, the decoder grid R = 30 .mu.m, the height H = 445 .mu.m and the decoder area per selected line FD = R .multidot. H = 13,350 .mu.m.sup.2.

For the known decoder circuit illustrated in FIG. 2, the decoder grid R = 19 .mu.m, the height H = 615 .mu.m and the decoder area per selected line FD = R .multidot. H = 11,685 .mu.m.sup.2.

The decoder circuit of the present invention can be constructed with the values in which the decoder grid R = 19 .mu.m, the height H = 540 .mu.m and the decoder area per selected line FD = R .multidot. H = 10,260 .mu.m.sup.2.

Although I have described my invention by reference to particular illustrative embodiments thereof, many changes and modifications of the invention may become apparent to those skilled in the art without departing from the spirit and scope of the invention. I therefore intend to include within the patent warranted hereon all such changes and modifications as may reasonably and properly be included within the scope of my contribution to the art.