T 0448/93 24-11-1994

Reasons for the Decision

1. The appeal complies with Article 106 to 108 and Rule 64 EPC and is, therefore, admissible.

2. Added Subject-Matter

2.1. Claim 1 of both the main and auxiliary requests includes, in addition to features clearly derivable from the application as originally filed, the feature "that said delivery means... does not comprise a capacitor element". The originally filed application makes no reference to a capacitor element and includes no suggestion that any advantage is derived from the absence of such an element.

2.2. The established jurisprudence of the Boards of Appeal, see e.g. T 4/80 OJ EPO 1982, 149, is that originally disclosed subject-matter may be excluded from a wider claim by a disclaimer if the subject-matter remaining in the claim cannot technically be defined directly (positively) more clearly and concisely. It is observed that a disclaimer is more usually used in the chemical field to limit the Applicant to a range of values narrower than that disclosed in the examples in the description. Reference is also directed to T 170/87, OJ EPO 1989, 441, in which it was stated that if a disclaimer is by way of insertion of a new feature, such that the technical teaching contained in the original documents would be substantially modified, then "this can be no more permissible by way of a disclaimer than it would be in any other way".

2.3. Nevertheless, the question of whether or not the present disclaimer is allowable or gives rise to objection under Article 123(2) EPC can in the Board's view - at least as regards the main request - be left undecided in view of the findings set forth below as regards clarity and inventive step. Although the Board would have been entitled to refuse to admit the claims to the proceedings - the amendment including the disclaimer having been filed for the first time in the course of the oral proceedings - it has taken the view that in the interest of procedural expediency the revised claims of both requests should be admitted so that the substantive issues may be decided.

2.4. The Board considers that despite clear difficulties with the language of the claims it is possible to discern the subject-matter underlying them and to apply Article 69 EPC and its Protocol to their interpretation, so that the substantive issues may be decided in the present proceedings.

3. Closest prior art

3.1. It is common ground that the single most relevant prior art document is D1. D1 discloses all the features of the preamble of Claim 1 of both requests. D1 also discloses at page 9, lines 4 and 5 the provision of an "abnormal condition detector" 26 connected via a signal line 24 to an external pin 22 of the integrated circuit. Detector 26. serves to detect the presence of a "normally disallowed state" on pin 22 and in response to place the circuit in a test mode. From page 10, lines 3 to 6 and from the arrangement of transistors 40 in Figure 2 it can be seen that the "normally disallowed state" is an abnormally high signal.

3.2. D1 thus discloses means connected to an external terminal for operating when a predetermined voltage outside the usual operating range is applied to the external terminal. These means do not include a capacitor element.

3.3. Claim 1 of both requests accordingly differs from the disclosure of D1 in specifying that the aforementioned means is delivery means (for delivering data) connected between the comparison means and the external terminal to which the predetermined voltage outside the usual operating range is applied. In accordance with D1 a separate terminal for data output and voltage input is provided. The subject-matter of Claim 1 of both requests is accordingly novel.

4. Inventive step (main request)

4.1. From the above it can be seen that the D1 arrangement has the disadvantage that two external connection terminals must be used in order to derive the comparison information. However, D1 also states at page 9, lines 12 to 17 that, although two separate terminals are illustrated, "a single external pin may be utilised ... such that signal line 24 would be interconnected to external pin 20". No embodiment incorporating this principle is shown but clearly the result of the comparison must in some way be indicated through the line receiving the predetermined voltage outside the usual operating range.

4.2. The subject-matter of Claim 1 accordingly adds to the known disclosure of D1 only that the result of the comparison is indicated by the current passing through the external terminal when the predetermined voltage is present. However, once a predetermined voltage is supplied to the terminal it is difficult to see how else this skilled person could measure data at this terminal. The Board accordingly concludes that the skilled person, given the disclosure of D1 and desiring to follow the suggested path of using only a single external terminal, would without the exercise of invention derive the result of the comparisons carried out by measuring the current passing through the external terminal when the predetermined voltage is applied. The subject-matter of Claim 1 of the main request accordingly lacks an inventive step.

5. Inventive step (auxiliary request)

5.1. Claim 1 of the auxiliary request differs from that of the main request in including the subject-matter of the original Claim 5. The claim is accordingly directed to those embodiments, such as the Figure 5 embodiment, which provide a status detection line. This line indicates when a coincidence is detected on any one of the address lines. In other words, whereas in the Figure 4. embodiment the line 31 gives an output when a complete address of a failed memory cell is detected - i.e. when all coincidence detection circuits indicate coincidence and the line 31 goes high - the Figure 5 embodiment gives an output on the status detection line 41 when one bit of the cell address is detected and any one of the coincidence detection circuits goes high. This appears to have the advantage that instead of cycling through all the memory addresses in order to detect a failed cell, requiring 2n+1 cycles, each address line can be addressed in turn, thereby determining from the individual address lines the failed cell and requiring only n+1 cycles. It is observed that this system would only appear to work if a single memory cell is defective, an issue not addressed in the application.

5.2. It is noted that the introduction to the description goes out from a state of the art according to which 2n+1 cycles are required to test a circuit, the object of the invention being stated to be the provision of "quick and correct detection" of the written state of the memory circuit. The Figure 4 embodiment would not appear to achieve this object, differing from the acknowledged prior art at Figure 1 only in the provision of the external terminal which - as noted at paragraph 4 above - is known per se from D1.

5.3. None of the prior art known to the Board discloses the use of memory testing by way of the individual address lines rather than the individual cells. Although in its decision the Examining Division does not explicitly discuss the subject-matter now included in Claim 1 of the auxiliary request it is noted that in its first communication the Examining Division drew attention to D1 at page 11, lines 19 to 22. However, although this refers to cycling through columns one at a time, it is clear in the context that this relates merely to the normal row and column select of a semiconductor memory rather than to individual address lines, the remainder of the cited paragraph in conjunction with Figure 3 making it clear that it is the memory cells rather than the address lines which are addressed individually. Attention is also directed to page 10, lines 27 to 35, according to which the decoder 70 is programmed with the address of a defective memory cell and "will respond to one particular combination of address inputs ... applied to the semiconductor memory to thereby generate a column of row select signal". The advantage in speed to be gained by addressing the memory lines rather than the individual cells is not derivable from D1 or from any other document of which the Board is aware.

5.4. It will be appreciated that the above analysis is primarily based on a comparison of the Figure 5 embodiment of the application with D1 rather than on a strict reading of the wording of the claim. The Board has adopted this comparison in the interest of procedural efficiency as the representative had made clear in the oral proceedings that Claim 1 of the subsidiary request was intended to embrace the Figure 5 embodiment, although in the Board's view the claim is insufficiently clear to enable grant at the present stage of the procedure.

5.5. It will be observed that in the above conclusion on inventive step no account has been taken of D2. The Appellant's arguments on this document are therefore irrelevant. It is however observed that the assertion that the presence of a capacitor would slow down this circuit appreciably is not accepted by the Board. In the first place, the capacitor - designated Q8 - is clearly an integrated circuit element formed by a transistor, as are all the other elements of the circuit. The capacitance is accordingly small. For the sake of completeness it is moreover observed that from D2 the skilled person learns - if he indeed needed to do so - that a single terminal supplied with a predetermined voltage could also be used as the data terminal; no invention can be seen in applying this knowledge to D1 at what ever speed that skilled person found necessary.

6. It is therefore necessary for the application to be remitted to the Examining Division for further prosecution on the basis of Claim 1 of the subsidiary request. It will be necessary for the Examining Division to consider, inter alia:

(a) whether the term "comparison means" can be used to cover both the means 24 serving to detect whether a fuse has been blown for any given memory bit and the overall assembly of coincidence detection circuits;

(b) whether the reference to the status detection means being for delivering a signal "for indicating the written state of one of a plurality of memory cells in said memory means" is consistent with line 2 of the claim and with the description, the expression "memory cell" being generally used to refer to the main memory and replacement memory cells rather than the address memory incorporating the fused links which is apparently meant;

(c) whether the claim makes sufficiently clear that detection of a coincidence by any one of the circuits 2 causes a signal to be delivered to the terminal;

(d) whether the disclaimer "and in that said delivery means does not comprise a capacitor" is necessary and is supported by the subject-matter of the application as originally filed;

(e) whether the subordinate claims, in particular Claims 3 and 4, are consistent with the appreciation of the invention now put forward in the independent claim of the subsidiary request;

(f) whether Claims 6 to 9 are either consistent with, or add anything to, the preceding claims; and

(g) whether any embodiments are no longer covered by the independent claim and should therefore be deleted from the application.