BIPOLAR-TRANSISTOR TYPE RANDOM ACCESS MEMORY DEVICE HAVING A REDUNDANCY CONFIGURATION

Abstract: A bipolar-transistor type RAM device, particularly an ECL type RAM device, includes a memory cell array (1), an address receiving circuit (2), a normal memory cell selecting circuit (14,3), and a redundancy configuration. The redun­ dancy configuration includes a redundancy memory cell array (7), a defective memory address storing circuit (9), an address comparing circuit (10), and a redundancy memory cell selecting circuit (8). The address comparing circuit directly receives the address signal and the defective mem­ ory address signal. The normal memory cell selecting circuit is energised when the address signal does not equal the defective memory address signal. Otherwise, the redun­ dancy memory cell selecting circuit is energised.

Description: This invention relates to a bipolar-transistor type random access memory (RAM) device having a redundancy configuration. More particularly, it relates to an emitter-coupled-logic (ECL) type RAM device having a redundancy configuration. In a RAM device, a large number of memory cells are arranged along rows and columns. The density of defects generated in such a semiconductor memory device during the manufacture thereof is relatively independent of the integration density of the device. Rather, it derives from the semiconductor manufacturing technology. In general, the higher the integration density of the device, the greater the ratio of normal memory cells to defective memory cells. This is one of the advantages of increasing the integration density of a semiconductor memory device. Even if a device includes only one defective memory cell, however, the device cannot be operated normally and, therefore, must be scrapped. As a result, despite the lower ratio of defective memory cells, greater integration density means reduced manufacturing yield. In a metal-insulator-semiconductor (MIS) type RAM, in order to overcome the problem of defective memory cells, use is made of redundancy memory cells. When a defective memory cell is detected, a redundancy memory cell row or column is selected instead of the memory cell row or column including the defective memory cell. In general, one or two redundancy memory cell rows or columns are usually provided. In the prior art, however, there has been no bipolar-transistor type RAM having a redundancy configuration, because there has been no redundancy configuration suitable for a bipolar-transistor type RAM, which operates at a much higher speed than a MIS type RAM. Also, there has not been any strong demand for a redundancy configuration in a bipolar-transistor type RAM, due to the comparatively small number of memory cells therein. With improvements in integration technology for bipolar-transistor type RAMs and the requirement for larger numbers of memory cells, however, bipolar-transistor type RAM devices having a large number of memory cells have come into demand. Accordingly, bipolar-transistor type RAMs having a redundancy configuration have also come into demand. EP-A-0087610 describes a bipolar-transistor type random access memory device, characterised by a memory cell array including a plurality of memory cells; a redundancy memory cell array including a plurality of memory cells; means for receiving an address signal; means, operatively connected to the address receiving means, for selecting a normal memory cell in the memory cell array in response to the address signal from the address receiving means; means for storing one or more defective memory addresses of one or more defective memory cells in the memory cell array; means, operatively connected to the defective address storing means, for receiving the address signal independently of the address receiving means and one or more defective memory address signals from the defective address storing means and for comparing the address signal with the defective memory address signals; and means, operatively connected to the address receiving and comparing means, for selecting a memory cell in the redundancy memory cell array corresponding to a defective memory cell in the memory cell array, the normal memory cell selecting means being energised when the address signal does not equal the defective memory address signal, the redundancy memory cell selecting means being energised otherwise. In accordance with the present invention, an emitter-coupled logic type random access memory device comprises a memory cell array including a plurality of memory cells and a plurality of address lines, each memory cell comprising an emitter-coupled-logic flip-flop; a redundancy memory cell array including a plurality of memory cells and a plurality of redundancy address lines, each memory cell comprising an ECL flip-flop; address signal input terminals for receiving address signals; means, connected to the address signal input terminals for receiving the address signals and including first ECL gate circuits outputting signals, each having: a first transistor having a base for receiving a bit of the address signals and having an emitter; a second transistor having an emitter coupled to the emitter of the first transistor; and first amplifying transistors for receiving the output signals from the first ECL gate circuits and amplifying the output signals; means operatively connected to the address receiving means, and including second ECL gate circuits, each having: a plurality of third transistors connected to receive the output signals from the first amplifying transistors and having an emitter; a fourth transistor having an emitter coupled to the emitters of the third transistors; and drive transistors connected to the address lines for driving the address lines in response to output signals from the second ECL gate circuits, for selecting a normal memory cell in the memory cell array in response to the address signals from the address receiving means; means for storing one or more defective memory addresses of one or more defective memory cells in the memory cell array; means, operatively connected to the defective address storing means and including third ECL gate circuits, each having: a fifth transistor having a base connected to receive the address signals; a sixth transistor for receiving the defective memory address signals and comparing the address signals and the defective memory address signals; and second amplifying transistor circuits connected to the fifth and sixth transistors, respectively, each having two amplifying transistors having emitters connected at a common node and having bases for receiving output signals from the fifth and sixth transistors, respectively, and amplifying the same, for receiving the address signals independently of the address receiving means and one or more defective memory address signals from the defective address storing means and for comparing the address signals with the defective memory signals; and means, operatively connected to the address receiving and comparing means and including fourth ECL gate circuits, each having: a seventh transistor having a base connected to the node of the amplifying transistors in the second amplifying transistor circuits for receiving a signal therefrom and having an emitter; an eighth transistor having an emitter coupled to the emitter of the seventh transistor and redundancy drive transistors, connected to the redundancy address lines, for driving respective redundancy address lines in response to output signals from the fourth ECL gate circuits, for selecting a memory cell in the redundancy memory cell array corresponding to a defective memory cell in the memory cell array, the normal memory cell selecting means, operatively connected to the node of the two amplifying transistors, being energised when the address signal does not equal the defective memory address signal, the redundancy memory cell selecting means being energised otherwise. The invention provides a redundancy configuration for a bipolar-transistor RAM device having the same operation time as the bipolar-transistor RAM device. The invention also provides a redundancy configuration suitable for an ECL type RAM device. Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a block diagram of a bipolar-transistor type RAM device having a redundancy configuration, in accordance with the present invention; Fig. 2 is a circuit diagram of the RAM device shown in Fig. 1, specifically for an ECL type RAM device; Fig. 3 illustrates signal characteristics for explaining the operation and functions of the circuit shown in Fig. 2; and Fig. 4 is a circuit diagram of an alternative form of the RAM device shown in Fig. 1. Referring to Fig. 1, a bipolar-type RAM device includes a normal configuration and a redundancy configuration. The normal configuration includes a memory cell array 1 having a plurality of memory cells in a matrix form with a plurality of word lines, for example 256 word lines in this embodiment, and a plurality of bit lines, for example 256 bit lines. Accordingly, the capacity of the memory cell array 1 is, for example, 256 x 256 bits, i.e. 64 K bits. The normal configuration includes a word address buffer 2 which receives a word address signal W-ADD consisting of A₀ to A₇ bits, a word address decoder 14 and a word address driver 3 which selectively drives the word lines in response to the word address signal W-ADD. The normal configuration also includes a bit address buffer 4 which receives a bit address signal B-ADD consisting of A₈ to A₁₅ bits, a bit address decoder 18, and a bit address driver 5 which selectively drives the bit lines in response to the bit address signal B-ADD. The normal configuration further includes an input and output (I/O) circuit 6 having 256 sense amplifiers, 256 write amplifiers and a control circuit thereof. In the circuit described above, the word address decoder 14 and the word address driver 3 may be constructed as one circuit unit. Similarly, the bit address decoder 18 and the bit address driver 5 may be constructed as one circuit unit. The redundancy configuration includes a redundancy memory cell array 7 having a plurality of redundancy memory cells associated with a redundancy word line and 256 redundancy bit lines. The redundancy configuration also includes a compare gate circuit 10 which receives the word address signal W-ADD and a defective word address signal DW-ADD from a programable read-only memory (PROM) 9, the PROM 9 storing the defective word address signal DW-ADD, and a redundancy word address driver 8 driving the redundancy word line in the redundancy memory cell array 7. In Fig. 1, each memory cell circuit in the redundancy memory cell array 7 is identical to a memory cell circuit in the memory cell array 1, resulting in the same operation time for each cell circuit. The signal processing speed from the compare gate circuit 10 to the redundancy word address driver 8 is approximately the same as that from the word address buffer 2 to the word address driver 3. This will be described in detail with reference to Fig. 1. The bit address driver 5 drives bit lines in both the memory cell array 1 and the redundancy memory cell array 7 concurrently. The (I/O) circuit 6 communicates with both the memory cell array 1 and the redundancy memory cell array 7 for reading-out or storing the data from or into one or other of the cell arrays. If a defective memory cell is detected in the memory cell array 1 during an operating test in a semifinished state of the bipolar-transistor type RAM device, such as in the wafer state, a word address signal W-ADD corresponding to the defective memory cell is stored in the PROM 9 in response to the application of a write signal WT to the PROM 9, as shown by the dotted lines. The operation of the bipolar-transistor type RAM device shown in Fig. 1 will now be described. When a write enable signal WE which is high level, designating a write mode, is applied to the (I/O) circuit 6, the word address signal W-ADD is supplied to the word address buffer 2 and the compare gate circuit 10. The compare gate circuit 10 compares the word address signal W-ADD with the defective word address signal DW-ADD from the PROM 9 and outputs a high level redundancy circuit selection signal SR when the address signals W-ADD and DW-ADD are identical or low level redundancy circuit selection signal SR otherwise. If a low level redundancy circuit selection signal SR is output, the word address decoder 14 and the word address driver 3 are energized. Accordingly, a signal of the word address signal W-ADD, which is amplified and shifted to a predetermined level at the word address buffer 2, is decoded at the word address decoder 14 to generate a word line selection signal applied to the word address decoder 14, resulting in the selection of the word line in the memory cell array 1 corresponding to the word address signal W-ADD by the word address driver 3. At the same time, the bit address signal B-ADD is supplied to the bit address buffer 4 in response to the application of a chip enable signal CS to the (I/O) circuit 6, amplifying and shifting it to a predetermined signal level. A signal output from the bit address buffer 4 is decoded at the bit address decoder 18 to generate a bit line selection signal applied to the bit address driver 5, resulting in the selection of the bit lines in the memory cell array 1 corresponding to the bit address signal B-ADD. As a result, an input data D IN supplied to the (I/O) circuit 6 is stored in the memory cells in the memory cell array 1, which are designated by the selected word line and the selected bit lines. On the contrary, if a high level redundancy circuit selection signal SR is output from the compare gate circuit 10, the redundancy word address driver 8 is energized instead of the word address decoder 14 and the word address driver 3 for the memory cell array 1. The redundancy word driver 8 activates the redundancy word line in the redundancy memory cell array 7. The selection of the bit lines in the redundancy memory cell array 7 is similar to that of the memory cell array 1 mentioned above. As a result, the input data D IN to the (I/O) circuit 6 is stored in the redundancy memory cells in the redundancy memory cell array 7 which are designated by the selected bit lines. The read-out operation from the memory cell array 1 or the redundancy memory cell array 7 is effected similar to the above operation, when the write enable signal WE is low level. In order to keep the high speed operation time of the redundancy configuration the same as the operation time of the normal configuration, the following design redundancy considerations have been made: (a) supplying directly the word address signal W-ADD to the compare gate circuit 10 in the redundancy configuration without passing through the word address buffer 2 like in a MIS type RAM device, (b) making the signal propagation time from the compare gate circuit 10 to the redundancy word address driver 8 the same as that from the word address buffer 2 to the word address driver 3 or making the number of circuit steps in the compare gate circuit 10 and the redundancy word address driver 8 the same as that in the word address buffer 2, the word address decoder 14, and the word address driver 3 with a same circuit construction, (c) making each memory cell circuit in the redundancy memory cell array 7 the same as that of the memory cell in the memory cell array 1, and (d) driving simultaneously the bit lines or the address lines in the redundancy memory cell array 7 with those in the memory cell array 1. The redundancy configuration shown in Fig. 1 can only cover one defective memory cell in each bit line. In order to cover a plurality of defective memory cells in a bit line in the memory cell array 1, a plurality of redundancy configurations, each of which consists of a compare gate circuit 10, redundancy word address driver 8, PROM 9 and redundancy memory cell array 7 are required. This may be applied to the word lines instead of the bit lines, mentioned above. Referring to Fig. 2, a specific circuit of an ECL type RAM device, an example of the bipolar-transistor type RAM device shown in Fig. 1, will be described. In Fig. 2, the memory cell array 1 includes a plurality of memory cells MC, only one of which is shown for simplifying the drawing. The memory cell MC is connected between a high-voltage word line WL i + and a low-voltage word line (or a holding line) WL i - and between a bit line BL j and an inverted bit line BL j , and forms a flip-flop circuit including pnp type transistors Q₁ and Q₂ and npn type multiemitter transistors Q₃ and Q₄. A constant current source IS₁ is provided between the low-voltage word line WL i -and a low-voltage power supply terminal V ee . The word address driver 3 includes a current switch circuit having npn type transistors Q₅ , Q₆ , and Q₇ , emitters of which are common-connected, a constant current source IS₂ connected between the common-connected point and the low-voltage power supply terminal V ee , a resistor R₁ connected between a high-voltage power supply terminal V cc and a common-connected point of collectors of the transistors Q₅ and Q₆ , and an npn type transistor Q₈ driving the high-voltage word line WL i +. The shown word address buffer 2 receives a bit A₀ of the word address signal W-ADD. The word address buffer 2 includes an emitter follower (or a level shift circuit) 2a and a current switch circuit 2b. The emitter follower 2a includes an npn type transistor Q₂₈ receiving the bit A₀ at a base thereof, a diode D₁ , and a constant current source IS₃ , series-connected between the high- and low-voltage power supply terminals V cc and V ee . The current switch circuit 2b includes a diode D₂ , a resistor R₂ , an npn type transistor Q₉ , and a constant current source IS₄. The current switch circuit 2b also includes a series circuit consisting of a resistor R₃ and an npn type transistor Q₁₀ , which is parallel- connected to a series circuit of the resistor R₂ and the transistor Q₉. A base of the transistor Q₉ is connected to a common-connected point of the diode D₁ and the constant current source IS₃. A base of the transistor Q₁₀ is supplied with a reference voltage VRF₁. The word address decoder 14 includes a decoding circuit 14b consisting of a plurality of signal lines, a plurality of constant current sources, each connected to the corresponding signal line of the decoding circuit 14b, and constant current sources IS₁₅ (only one current source shown for simplifying the drawing). The word address decoder 14 also includes a circuit 14a having an npn type multiemitter transistor Q₁₁ , for selecting the signal lines of the decoding circuit 14b. A base of the transistor Q₁₁ is connected to a collector of the transistor Q₁₀ in the current switch circuit 2b. The circuit 14a includes another npn type multiemitter transistor (not shown) between a collector of the transistor Q₉ and the decoding circuit 14b, similar to the transistor Q₁₁. The line connection between emitters of the transistors in the circuit 14a and the signal lines in the decoding circuit 14b and between the signal lines in the decoding circuit 14b and bases of the transistors Q₅ and Q₆ in the word address driver 3 defines the selection of the word line WL. The bit address driver 5, represented in the drawing by a single circuit for driving a pair of bit lines BL j and BL j for simplifying the drawing, includes npn type multiemitter transistors Q₂₂ and Q₂₃ , an npn type transistor Q₂₄ , and constant current sources IS₁₂ , IS₁₃ , and IS₁₄ , each connected between respective emitters of the above transistors and the low-voltage power supply terminal V ee . The bit address driver 5 also includes a pair of transistors Q₂₅ and Q₂₆ and a pair of transistors Q₂₇ and Q₂₈. The (I/O) circuit 6 includes a sense amplifier circuit 6a, a chip select buffer 6b, and a read-write control and write amplifier circuit 6c. The sense amplifier circuit 6a is connected to collectors of the transistors Q₂₅ and Q₂₆ , and reads the voltage between the bit lines BL j and BL j as read-out data D OUT . The read-write control and write amplifier circuit 6c, specifically the write amplifier (not shown), is connected to bases of the transistors Q₂₇ and Q₂₈ , storing input data D IN a desired memory cell MC. The read-write control and write amplifier circuit 6c controls the above read-out and storing operation in response to a write enable signal WE. The chip select buffer 6b triggers the sense amplifier circuit 6a and the read-write control and write amplifier circuit 6c in response to a chip select signal CS. Detailed circuits of the bit address buffer 4 and the bit address decoder 18 are similar to those of the word address buffer 2 and the word address decoder 14 and, thus, are not explained. The compare gate circuit 10, represented in the drawing by a single circuit for the A₀ bit of the word address information W-ADD for simplifying the drawing, includes an emitter follower 10a, a compare circuit 10b, and an OR gate output circuit 10c. The circuits 10b and 10c form an exclusive-OR (EOR) circuit. The emitter follower 10a includes an npn type transistor Q₁₂ receiving the A₀ bit of the word address signal W-ADD at a base thereof, a diode D₃ , and a constant current source IS₅ , series-connected between the high- and low-voltage power supply terminals V cc and V ee . The compare circuit 10b includes resistors R₄ , R₅ and R₆ , npn type transistors Q₁₃ , Q₁₄ , Q₁₅ and Q₁₆ , and constant current sources IS₆ and IS₇. A base of the transistor Q₁₃ is connected to an emitter of the transistor Q₁₂ through the diode D₃. Bases of the transistors Q₁₄ end Q₁₅ are supplied with reference voltages VRF₂ and VRF₃ , which may be the same voltage. A base of the transistor Q₁₆ is supplied with an A₀ bit of the defective word address information DW-ADD from the PROM 9 shown in Fig. 1, when the corresponding defective memory cell address is stored in the PROM 9. The output circuit 10c includes npn type transistors Q₁₇ and Q₁₈ , functioning as an OR gate, end a constant current source IS₈. At a node N₁₀ connected to a base of the transistor Q₇ and to a base of a transistor Q₁₉ , described later, an output of the output circuit 10c, common-connected with emitters of the transistors Q₁₇ and Q₁₈ , is common-connected to other outputs from other output circuits in other compare circuits (not shown) in the compare gate circuit 10 for A₁ to A₇ bits of the word address signal W-ADD, supplying a redundancy circuit selection signal SR to the transistors Q₇ and Q₁₉. The redundancy word driver 8 includes npn type transistors Q₁₉ and Q₂₀ , forming a differential circuit, a constant current source IS₉ , a resistor R₇ , and an npn type transistor Q₂₁ driving a redundancy high-voltage word line WL(R)+ in the redundancy memory cell array 7. A redundancy memory cell MC(R), consisting of pnp type transistors Q₇₁ and Q₇₂ and npn type multiemitter transistors Q₇₃ and Q₇₄ forming a flip-flop, is provided between the high-voltage word line WL(R)+ and a redundancy low-voltage word line WL(R)- connected to a constant current source IS₁₀ discharging current thereon and between the high- and low-voltage bit lines BL j and BL j . The circuit of the redundancy memory cell MC(R) is identical to that of the memory cell MC in the memory cell array 1. One pair of redundancy word lines WL(R)+ and WL(R)- are provided in the redundancy memory cell array 7. A plurality of pairs of bit lines BL and BL are commonly provided in the memory cell array 1 and the redundancy memory cell array 7. The operation of the compare gate circuit 10 will be described with reference to Fig. 3. The compare gate circuit 10 includes the EOR circuit of the compare circuit 10b and the OR gate output circuit 10c. The EOR circuit outputs the lowest voltage VL₂ of the redundancy circuit selection signal SR when the word address signal W-ADD matches the defective word address signal DW-ADD from the PROM 9 and the voltage VH₂ of the selection signal SR otherwise. When the A₀ bit of the word address signal W-ADD is high level, the transistor Q₁₂ is turned ON, resulting in the transistor Q₁₃ being ON and thus the transistor Q₁₄ OFF. When the A₀ bit of the defective word address signal DW-ADD from the PROM 9 is also high level, the transistor Q₁₆ is turned ON and thus the transistor Q₁₅ is turned OFF. The bases of the transistors Q₁₇ and Q₁₈ are supplied with low level voltage, maintaining the transistors Q₁₇ and Q₁₈ OFF. As a result, the output of the OR gate output circuit 10c is low level. On the other hand, when the A₀ bit of the word address signal W-ADD is high and the A₀ bit of the defective word address signal DW-ADD is low, the transistor Q₁₆ is turned OFF and thus the transistor Q₁₅ is turned ON, resulting in the transistor Q₁₈ being OFF. The transistor Q₁₄ is turned OFF, resulting in the transistor Q₁₇ being ON and thus rendering the redundancy circuit selection signal SR the high level VH₂. In addition, when the A₀ bit of the word address signal W-ADD is low and the A₀ bit of the defective word address signal DW-ADD is high, opposite to the above, the transistor Q₁₇ is turned ON and the transistor Q₁₈ is turned OFF, resulting in a high level VH₂ of the redundancy circuit selection signal SR. Furthermore, when both the A₀ bits of the word address signal W-ADD and the defective word address signal DW-ADD are low level, the transistor Q₁₃ is turned OFF, the transistor Q₁₄ is turned ON, the transistor Q₁₅ is turned ON, and the transistor Q₁₆ is turned OFF. Thus, the transistors Q₁₇ and Q₁₈ are turned OFF, resulting in a low level of the redundancy circuit selection signal SR. The above operation can be applied to the operation for other bits A₁ to A₇ of the word address signal W-ADD and other bits A₁ to A₇ of the defective word address signal DW-ADD. Accordingly, when all bits of the word address signal W-ADD are identical to those of the defective word address signal DW-ADD, the redundancy circuit selection signal SR at the node N₁₀ becomes the lowest level VL₂. The resistor R₄ shifts the low level of the redundancy circuit selection signal SR from the normal low level VL₁ in the device to the lowest level VL₂ by a voltage ΔVL. The level shift is of significance for the word line selection mentioned later. The operation of the ECL type RAM device shown in Fig. 2 will be described. The word address signal W-ADD, the bit address signal B-ADD, the chip select signal CS having the high level, and the write enable signal WE having the low level indicating the read-out operation are supplied to the RAM device. When the word address signal W-ADD does not match any defective word address signals DW-ADD, the current switch circuits 2b in the word address buffer 2 are operated in response to A₀ to A₇ bits of the word address signal W-ADD to energize the word address decoder 14. The base of the transistor Q₇ in the word address driver 3 is supplied with the high level VH₂ of the redundancy circuit selection signal SR, which is between the high level voltage VH₁ and low level voltage VL₁. When the voltage applied to the bases of the transistors Q₅ and Q₆ in the word address driver 3 is low due to the decoding in the word address decoder 14, the transistor Q₈ in the word address driver 3 is turned ON, driving the high-voltage word line WL i +. At the same time, a bit line selecting signal from the bit address decoder 18, corresponding to the bit address signal B-ADD applied to the bit address buffer 4, is supplied to bases of the transistors Q₂₂ to Q₂₄ in the bit address driver 5, turning these transistors ON, and thus driving the bit lines BL j and BL j . The voltage on the bit lines BL j and BL j responsive to store data in the memory cell MC in the memory cell array 1 is transferred into the compare transistors Q₂₅ and Q₂₆ , reading-out the data D OUT responsive to the difference of the transferred voltage in the transistors Q₂₅ and Q₂₆ through the sense amplifier circuit 6a. Upon the reading-out, the chip select signal CS and the write enable signal WE are restored. During the above operation, the redundancy circuit selection signal SR of the high level VH₂ is supplied to the base of the transistor Q₁₉ in the redundancy word driver 8, resulting in the transistor Q₁₉ being ON. The transistor Q₂₁ is OFF, therefore, the redundancy high-voltage word line WL(R)+ is deenergized. When the write enable signal WE is high level, designating the store operation, the transistors Q₂₇ and Q₂₈ are turned ON or OFF in response to the input data D IN to render the bit lines BL j and BL j high or low level, storing the input data D IN in the desired memory cells in the memory cell array 1. When the word address signal W-ADD matches the defective word address signal DW-ADD, the redundancy circuit selection signal SR of the low level VL₂ , lower than the normal low level VL₁ , is supplied to the bases of the transistors Q₇ and Q₁₉. The transistor Q₇ is cut OFF, and thus the transistor Q₅ or Q₆ is turned ON, deenergizing the high-voltage word line WL i +. On the other hand, the transistor Q₁₉ in the redundancy word driver 8 is cut OFF and the transistor Q₂₀ is turned ON. The value of the reference voltage VRF₄ applied to the base of the transistor Q₂₀ is between the high level VH₂ and the low level VL₂ of the redundancy circuit selection signal SR. The transistor Q₂₁ in the redundancy word address driver 8 is turned ON, energizing the redundancy word line WL(R)+, and thus effecting the read-out or store operation to the redundancy memory cells MC(R) in the redundancy memory cell array 7. The bit A₀ of the word address signal W-ADD is transferred to the emitter follower 2a, the current switch circuit 2b, the circuit 14a including the transistor Q₁₁ , the circuit of the transistors Q₅ to Q₇ , and the transistor Q₈ , i.e., a total five stage circuits, to the word line WL i +. Similarly, the bit A₀ of the word address signal W-ADD is transferred to the emitter follower 10a, the compare circuit 10b, the OR gate output circuit 10c, the circuit of the transistors Q₁₉ and Q₂₀ , and the transistor Q₂₁ , i.e., also a total five stage circuits, to the redundancy word line WL(R)+. Consequently, the selection time of the redundancy word line WL(R)+ is comparable with the selection time of the word line WL i +. In the ECL type RAM device, which must be kept in high speed operation even in access to the redundancy memory cell array 7, this is of great significance. Figure 4 is a circuit diagram of another embodiment of the ECL type RAM device corresponding to the circuit shown in Fig. 2. The emitter follower 2a in the word address buffer 2 in Fig. 2 is omitted. An address receiving circuit 20 having the same circuit configuration of the omitted emitter follower 2a is added at a preceding step of a word address buffer 2' including the current switch circuit 2b. The emitter follower 10a in the compare gate circuit 10 shown in Fig. 2 is also omitted. The bases of the transistors Q₁₃ and Q₉ are connected to a cathode of the diode D₁ in the address receiving circuit 20, i.e., the emitter follower. In Fig. 2, the emitter follower 2a is identical to the emitter follower 10a. Thus, the latter can be omitted, simplifying the compare gate circuit 10, as shown by a compare gate circuit 10'. The circuit operation is similar to that mentioned above and thus is not explained. A plurality of redundancy configurations, each having the compare gate circuit 10 or 10', the redundancy word address driver 8, and the redundancy memory cell array 7, may be provided. A redundancy configuration for bit lines may be provided instead of the redundancy configuration for word lines mentioned above.

Claims: An emitter-coupled-logic type random access memory device, characterised by a memory cell array (1) including a plurality of memory cells (MC) and a plurality of address lines, each memory cell (MC) comprising an emitter-coupled-logic (ECL) flip-flop; a redundancy memory cell array (7) including a plurality of memory cells and a plurality of redundancy address lines, each memory cell comprising an ECL flip-flop; address signal input terminals for receiving address signals; means (2), connected to the address signal input terminals for receiving the address signals (W-ADD) and including first ECL gate circuits outputting signals, each having: a first transistor (Q₉) having a base for receiving a bit of the address signals and having an emitter; a second transistor (Q₁₀) having an emitter coupled to the emitter of the first transistor (Q₉); and first amplifying transistors (Q₁₁) for receiving the output signals from the first ECL gate circuits and amplifying the output signals; means (14, 3), operatively connected to the address receiving means, and including second ECL gate circuits, each having: a plurality of third transistors (Q₅, Q₆) connected to receive the output signals from the first amplifying transistors (Q₁₁) and having an emitter; a fourth transistor (Q₇) having an emitter coupled to the emitters of the third transistors (Q₅, Q₆); and drive transistors (Q₈) connected to the address lines for driving the address lines in response to output signals from the second ECL gate circuits, for selecting a normal memory cell (MC) in the memory cell array (1) in response to the address signals from the address receiving means; means (9) for storing one or more defective memory addresses (DW-ADD) of one or more defective memory cells in the memory cell array; means (10), operatively connected to the defective address storing means and including third ECL gate circuits, each having: a fifth transistor (Q₁₃) having a base connected to receive the address signals; a sixth transistor (Q₁₆) for receiving the defective memory address signals and comparing the address signals and the defective memory address signals; and second amplifying transistor circuits connected to the fifth and sixth transistors (Q₁₃, Q₁₆), respectively, each having two amplifying transistors (Q₁₈, Q₁₇) having emitters connected at a common node (N10) and having bases for receiving output signals from the fifth and sixth transistors (Q₁₃, Q₁₆), respectively, and amplifying the same, for receiving the address signals independently of the address receiving means and one or more defective memory address signals from the defective address storing means and for comparing the address signals with the defective memory signals; and means (8), operatively connected to the address receiving and comparing means and including fourth ECL gate circuits, each having: a seventh transistor (Q₁₉) having a base connected to the node (N10) of the amplifying transistors (Q₁₈, Q₁₇) in the second amplifying transistor circuits for receiving a signal therefrom and having an emitter; an eighth transistor (Q₂₀) having an emitter coupled to the emitter of the seventh transistor (Q₁₉) and redundancy drive transistors (Q₂₁) , connected to the redundancy address lines, for driving respective redundancy address lines in response to output signals from the fourth ECL gate circuits, for selecting a memory cell (MC(R)) in the redundancy memory cell array corresponding to a defective memory cell in the memory cell array, the normal memory cell selecting means (14, 3), operatively connected to the node (N10) of the two amplifying transistors (Q₁₈, Q₁₇) , being energised when the address signal does not equal the defective memory address signal, the redundancy memory cell selecting means (8) being energised otherwise. An emitter-coupled-logic type random access memory device according to claim 1, characterised by an emitter follower-circuit (20), connected to one of the address signal input terminals, for receiving and level-shifting one of the address signals (W-ADD), and by the base of the first transistor (Q₉) of one of the first ECL gate circuits and the base of the fifth transistor (Q₁₃) of one of the third ECL gate circuits being connected to said emitter follower circuit (20) for receiving one of said level-shifted address signals. An emitter-coupled-logic type random access memory device according to claim 1, characterised by: a first emitter follower circuit (2a) connected to one of the address signal input terminals for receiving and level-shifting one of the address signals (W-ADD) to provide a first level-shifted address signal, the base of the first transistor (Q₉) of one of the first ECL gate circuits being connected to said first emitter follower circuit (2a) for receiving one of said first level-shifted address signals, and by a second emitter follower circuit (10a) also connected to one of the address signal input terminals for receiving and level-shifting one of the address signals (W-ADD) to provide a second level-shifted address signal, the base of the fifth transistor (Q₁₃) of one of the third ECL gate circuits being connected to said second emitter follower circuit (10a) for receiving one of said second level-shifted address signals.

Inventors: AWAYA, TOMOHARU, FUKUSHI, ISAO
Applicants: FUJITSU LIMITED
Application year: 1985
Main classification: G06F11
IPC codes: G11C29