Semiconductor memory devices having level converters

Abstract: A semiconductor memory device includes a plurality of level converters (12), each of the level converters including a bridge circuit constituted by four MOS transistors (T₁₁ to T₁₄) having one type of conductivity, gates of one pair (T₁₁, T₁₂) of four transistors, opposing each other, receiving a first signal ( e ) and gates of the other pair (T₁₃, T₁₄) of four transistors, opposing each other, receiving a signal ( f ) complementary to the first signal; a pair of complementary MOS inverter circuits to which a second signal ( a ) and a signal ( b ) complementary to the second signal are input, respectively, the outputs of the pair of inverter circuits being connected respectively to a first pair ( c , d ) of opposing connecting nodes of the bridge circuit; and a flip-flop circuit connected between a second pair of opposing connecting nodes of the bridge circuit, to thereby output a third signal ( g ) and a signal ( j ) complementary to the third signal from the second pair of connecting nodes respectively.

Description: The present invention relates to semiconductor memory devices having level converters. A semiconductor memory device may have a level converter in which the potential levels of a pair of mutually complementary output signals of the level converter are changed (i.e., inverted) in accordance with the potential level of a control signal supplied from a circuit for controlling an inversion or non-inversion of an address bit signal in accordance with data stored therein (e.g. a logic level of an address bit corresponding to a portion of a standard memory cell array having a defective memory cell thereamong). In a semiconductor memory device comprising complementary MOS (CMOS) circuits, portions of the semiconductor memory device (e.g. address buffer circuits to which corresponding address bit signals are input) may consist of circuitry comprising bipolar transistors (e.g. circuitry including emitter coupled logic gates) to increase the operational speed of the memory device. Such a semiconductor memory device is called a "BiCMOS" memory device. In such a semiconductor memory device, level converters are provided between the respective address buffer circuits including emitter coupled logic gates constituted by NPN type bipolar transistors and a decoder circuit constituted by MOS transistors, for example, to convert the logic amplitude (i.e. the potential difference between a high logic level and a low logic level) of the output signals supplied from each of the address buffer circuits to a value different from that of the above output signals (i.e., to a larger value needed for operating the decoder circuit constituted by MOS transistors). Further, in such a semiconductor memory device, control circuits are provided for controlling the inversion or non-inversion of a corresponding address bit signal in accordance with data stored therein (e.g., a logic level of corresponding address bit corresponding to a portion of a standard memory cell array having a defective memory cell therein). Accordingly, a portion of the standard memory cell array corresponding to a predetermined address (e.g., a predetermined row address) is selected through the decoder circuit, in accordance with the potential levels of the address bit signals supplied from each of the level converters, when at least one logic level of the input address bit signals does not coincide with that of the data stored in the corresponding control circuit. Further, a redundancy memory cell array is selected through a circuit for controlling a switch from the standard memory cell array to the redundancy memory cell array, instead of the portion of the standard memory cell array having the defective memory cell therein, when each logic level of the input address bit signals coincides with that of the data stored in the corresponding control circuit. To attain the above-mentioned operation, in a conventional address buffer circuit used in such a semiconductor memory device, a circuit configuration comprising emitter coupled logic gates connected in series is adopted, to which gates are input the corresponding address bit signal and the control signal supplied from the circuit for controlling the inversion or non-inversion of the address bit signal in accordance with data stored therein, so that the potential levels of a pair of signals output from the address buffer circuit may be changed (i.e. inverted) in accordance with the potential levels of the above address bit signal and the above control signal. A level converter previously used with such an address buffer circuit in a semiconductor memory device may be considered to comprise a bridge circuit having a first MOS transistor which is connected through a first node of the circuit to a second MOS transistor which is connected through a second node of the circuit to a third MOS transistor which is connected through a third node of the circuit to a fourth MOS transistor which is connected through a fourth node of the circuit to the said first MOS transistor, the four MOS transistors all being of the same conductivity type, respective gate electrodes of the first and third MOS transistors being connected to receive a first input signal from addressing circuitry (i.e. an address buffer circuit) of the device, respective gate electrodes of the second and fourth MOS transistors being connected to receive from the addressing circuitry an input signal complementary to the said first input signal, and the said second and fourth nodes being connected to deliver respective mutually-complementary output signals of the level converter to a subsequent stage of the device. Nevertheless, problems can arise in such a semiconductor memory device in that, because the address buffer circuit is constituted by emitter coupled logic gates connected in series, a margin for the power supply potential applied to the address buffer circuit is reduced, and thus it may be impossible to obtain a sufficient logic amplitude (i.e. sufficient potential difference between the high and low logic levels) for the above-mentioned input signals supplied to the level converter by the associated address buffer circuit, and further, the speed of operation of the level converter is reduced. It is accordingly desirable to increase the margin for the power supply potential applied to the address buffer circuit and to lower the low potential level of the output signal supplied from the address buffer circuit to the level converter, to thus increase the level conversion speed of the level converter, by constituting the level converter as a circuit wherein the inversion or non-inversion of the address bit signal based on the above control signal can be controlled within the level converter, and further, by enabling the address buffer circuit used in the memory device of this type to have a usual current switch configuration including only the emitter coupled logic gate to which the address bit signal and the reference signal are input. According to the present invention there is provided, in a semiconductor memory device, a level converter comprising a bridge circuit having a first MOS transistor which is connected through a first node of the circuit to a second MOS transistor which is connected through a second node of the circuit to a third MOS transistor which is connected through a third node of the circuit to a fourth MOS transistor which is connected through a fourth node of the circuit to the said first MOS transistor, the four MOS transistors all being of the same conductivity type, respective gate electrodes of the first and third MOS transistors being connected to receive a first input signal from addressing circuitry of the device, respective gate electrodes of the second and fourth MOS transistors being connected to receive from the addressing circuitry an input signal complementary to the said first input signal, and the said second and fourth nodes being connected to deliver respective mutually-complementary output signals of the level converter to a subsequent stage of the device; characterised in that the said first and third nodes are connected to receive respective mutually-complementary voltage signals determined by control circuitry of the device for applying thereto the said mutually-complementary input signals. In such a level converter the potential levels of the first and third connecting nodes are output respectively as the mutually-complementary output signals by way of a pair of the four MOS transistors that are turned-ON in accordance with the potential levels of the first input signal and the input signal complementary to the first input signal. In a preferred embodiment the first and third connecting nodes are connected to respective outputs of a pair of CMOS inverter circuits, so that the potential levels of those nodes can be changed from a low level to a high level, and vice versa, (i.e. inverted) in accordance with the potential levels of mutually-complementary control signals applied respectively to the inputs of the CMOS inverter circuits by the control circuitry of the semiconductor memory device. Reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 (comprising Figs. 1A and 1B) is a block diagram of an example of the overall construction of a semiconductor memory device having level converters, Figures 2A and 2B are circuit diagrams showing details of a first device according to Figure 1, Fig. 3 is a circuit diagram showing details of a second device embodying the present invention, according to Fig. 1, and Figs. 4A and 4B are circuit diagrams indicating different operation conditions of part of the circuit shown in Fig. 3. In Fig. 1, reference numeral 11′ denotes an address buffer circuit to which a row address bit signal A₀ and a reference signal (not shown in Fig. 1) are input, and a signal e and a signal f complementary to the signal e having predetermined potential levels, respectively, are output from the circuit 11′ in accordance with the potential level of the input address bit signal A₀. At reference numeral 13′ is a circuit for controlling the inversion or non-inversion of the address bit signal, and a signal R and a signal R complementary to the signal R and having predetermined potential levels, respectively, are output from the circuit 13′ in accordance with data stored in the above circuit 13′ (e.g., a logic level of a row address bit corresponding to a portion of a standard memory cell array which includes a defective memory cell therein). The potential levels of the above signals e and f are changed (i.e., are inverted) in accordance with not only the potential level of the input address bit signal A₀ , but also the potential levels of the above signals R and R . The address buffer circuit 11′, is generally constituted by emitter coupled logic gates (i.e., an ECL circuit construction formed by NPN type bipolar transistors) connected in series, and thus the logic amplitude (i.e., the potential difference between the high logic level and low logic level) of the signals e and f output from the address buffer circuit 11′ is made a predetermined value determined by the above ECL circuit construction connected in series. Reference numeral 12′ denotes a level converter to which the above signals e and f are input from the circuit 11 ,and a signal j and a signal g complementary to the signal j are supplied from the level converter 12′ to a row decoder 2. In this connection, the level converter 12′ converts the logic amplitude (i.e., the potential difference between the high logic level and low logic level) of the above signals j and g to a value different from that of the above signals e and f (i.e., to the larger value needed for operating a row decoder which is generally constituted by MOS transistors). As shown in Fig. 1, a portion 1-0 enclosed by a dot-dash line includes the above circuits 11′, 13′, and the level converter 12′, and portions 1-1 to 1-n to which address bit signals A₁ to A n are input, respectively, have a construction similar to that of the portion 1-0. The signals output from each of the level converters provided in the portions 1-1 to 1-n (corresponding to the signals j and g output from the portion 1-0) are also supplied to the row decoder 2 to which a word driver for the standard memory cell array is connected. A standard memory cell array 5 is constituted by predetermined number of portions of the standard memory cell array 5-0 to 5-m, which have separate row addresses allocated thereto, respectively. Also, a redundancy memory cell array 6 is provided and can be selected through a word driver 8 for the redundancy memory cell array instead of a portion of the standard memory cell array which includes a defective memory cell. Accordingly, a portion of the standard memory cell array corresponding to a predetermined row address (e.g., 5-0) is selected through the row decoder and the word driver 2 for the standard memory cell array, in accordance with the potential levels of the row address bit signals supplied from each of the above level converters, when at least one logic level of the input row address bit signals A₀ to A n does not coincide with that of the data stored in the corresponding circuit 13′. Further, the redundancy memory cell array 6 is selected through a circuit 7 (in this case, an OR gate 7) for controlling a switch from the standard memory cell array to the redundancy memory cell array and the word driver 8 for the redundancy memory cell array, instead of the portion of the standard memory cell array which includes a defective memory cell, when each logic level of the input address bit signals A₀ to A n coincides with that of the data stored in the corresponding circuit 13′. For example, where the input row address bit signals are constituted by A₀ to A₃ and a portion of the standard memory cell array corresponding to row address "0, 1, 1, 0" includes the defective memory cell, and further, the second and third address bit signals A₁ and A₂ among the above address bit signals A₀ to A₃ are inverted by the data stored in the above control circuit 13′ provided in the corresponding portion (i.e., 1-1 and 1-2), then if each of the row address bit signals "0, 1, 1, 0" is input from an external source to the corresponding address buffer circuit, the row address bit signals supplied from the respective portions 1-0 to 1-3 to the row decoder 2 become "0, 0, 0, 0" due to the inversion of the second and third address bit signals A₁ and A₂. Accordingly, the portion of the standard memory cell array corresponding to the row address "0, 0, 0, 0" is selected through the row decoder 2. On the other hand, if each of the row address bit signals "0, 0, 0, 0" is input from the external source to the corresponding address buffer circuit, the row address bit signals supplied from the respective portions 1-0 to 1-3 to the row decoder 2 become "0, 1, 1, 0" (i.e., the row address corresponding to the portion of the standard memory cell array including the defective memory cell), due to the above inversion of the signals A₁ and A₂. But, in this case, the output potential of the control circuit 7 (i.e., the OR gate 7) to which each of the address bit signals "0, 0, 0, 0" is input becomes low level, and therefore, the redundancy memory cell array 6 is selected through the word driver 8, but at this time the portion of the standard memory cell array including the above defective memory cell is not selected, owing to the supply of the above low level signal output from the control circuit 7 to the row decoder 2. Also, in Fig. 1, reference numeral 3 denotes a column decoder having a multiplexer provided therein. Column address bit signals A₀′ to A n ′ are input from the external source to the column decoder 3, and a predetermined memory cell provided in the portion of the standard memory cell array (e.g., 5-0), selected through the row decoder and word driver 2 or provided in the redundancy memory cell array 6, is selected for writing data D in to the above selected memory cell or reading data D out from the above selected memory cell, in accordance with the potential levels of the input column address bit signals A₀′ to A n ′. In this connection, a control circuit 4 for a data write or data read operation is provided to cause the multiplexer to select the data write operation of the data D in for the selected memory cell or the data read operation of the data D out from the selected memory cell. Also, a write enable signal and a chip select signal and so on, are generally supplied from the external source to the above control circuit 4. In the above Fig. 1, portions 1-0 to 1-n. each including the address buffer circuit 11′, the above control circuit 13′, and the level converter 12′, are provided to supply row address bit signals having predetermined potential levels from the external source to the row decorder 2, and portions similar to those above-mentioned can be provided to supply predetermined column address bit signals from the external source to the column decoder 3. Figures 2A and 2B are circuit diagrams illustrating an example of a circuit corresponding to a portion 1-0 shown in Fig. 1. In the address buffer circuit 11′ shown in Fig. 2A, reference characters T₁ , T₂ , T₂′, T₃ , T₃′, and T₄ to T₇ are NPN type bipolar transistors, reference characters R₁ and R₂ are resistors, and reference characters I₁ to I₄ are constant current sources. The emitters of a pair of transistors T₂ and T₃ and the emitters of a pair of transistors T₂′ and T₃′ are connected in common, and thus two emitter coupled logic gates (ECL gates) are constituted by the two pairs of transistors, T₂ and T₃, and T₂′, and T₃′. The address bit signal A₀ is input to the base of the transistor T₁ , and accordingly, the potential of the emitter of the transistor T₁ is supplied to the bases of the transistors T₂ and T₃′, respectively. Further, the potential of the reference signal V ref is supplied to the bases of the transistors T₃ and T₂′, respectively. Furthermore, the emitters of a pair of transistors T₆ and T₇ are connected in common, and the collectors of the transistors T₆ and T₇ are connected to the connecting points of the emitters of the above transistor pairs T₂ and T₃, and T₂′, and T₃′, respectively. Therefore, the ECL gate constituted by the transistors T6 and T7 is connected in series to the above two ECL gates constituted by the transistors T₂ and T₃ and T₂′ and T₃′. The signal R and the signal R complementary to the signal R are supplied from the circuit 13′ for controlling the inversion or non-inversion of the address bit signal, to the bases of the transistors T₆ and T₇ , respectively. Reference symbols V CC and V EE indicate upper and lower power source potentials, respectively. In the above address buffer circuit 11′, when the address bit signal A₀ having a high potential (e.g., -0.8 volts) is input to the base of the transistor T₁, a predetermined high potential based on the above address bit signal A₀ is supplied to the bases of the transistors T₂ and T₃′, as indicated by symbols "H" in Fig. 2A. Also, the potential of the reference signal V ref is supplied to the bases of the transistors T₃ and T₂′, as above-mentioned, and thus the transistors T₂ and T₃′ are turned-ON but the transistors T₃ and T₂′ are turned-OFF. Further, if it is assumed that the potentials of the above signals R and R , output from the circuit 13′ in accordance with the data stored in the circuit 13′, are high and low, as indicated by symbols "H" and "L", respectively, the transistor T₆ is turned-ON and the transistor T₇ is turned-OFF. Accordingly, a predetermined current flows from V CC to V EE through the resistor R₁ , the turned-ON transistors T₂ and T₆ connected in series, and the constant current source I₂ , and as a result, the base potential of the transistor T₄ becomes low level due to the potential drop produced through the resistor R₁ , and accordingly, the emitter potential of the transistor T₄ (i.e., the potential of the signal e ) becomes low level (i.e., -2.4 volts). On the other hand, the base potential of the transistor T₅ is maintained at a high level (in this case, 0 volt) due to the cut-0FF of the transistors T₃ and T₇ , and thus the emitter potential of the transistor T₅ (i.e., the potential of the signal f ) becomes high level (i.e., -0.8 volts). In this connection, when the potential of the above address bit signal A₀ is low (e.g., -1.6 volts), the transistors T₃ and T₂′ are turned-ON but the transistors T₂ and T₃′ are turned-OFF. Also, if it is assumed that the potentials of the signals R and R are low and high, in accordance with the data stored in the circuit 13′, respectively, the transistor T₆ is turned-OFF and the transistor T₇ is turned-ON. Therefore, the potentials of the above signals e and f output from the address buffer circuit 11′ are changed from low level to high level, and vice versa, (i.e., inverted) in accordance with not only the potential level of the input address bit signal A₀ but also the potential levels of the signals R and R supplied from the circuit 13′. The signals e and f output from the address buffer circuit 11′ are then supplied to the level converter 12′, in which a predetermined logic amplitude (in this case, [-0.8 - (-2.4)] = 1.6 volts) of the signals e and f complementary to each other is converted to the larger value needed for operating a decoder circuit constituted by MOS transistors. The level converter 12′ comprises four P channel type MOS transistors T₁₁ to T₁₄ , as indicated by symbols "P", and a flip-flop circuit constituted by two N channel type MOS transistors T₁₉ and T₂₀. In this connection, the above four transistors T₁₁ to T₁₄ are successively connected so that a bridge circuit as shown in Fig. 4A is constituted. The signal e is supplied to gates of a pair of MOS transistors T₁₁ and T₁₂ (i.e., a pair of opposing MOS transistors in the above bridge circuit), and the signal f is supplied to gates of the other pair of MOS transistors T₁₃ and T₁₄ (i.e., the other pair of opposing MOS transistors in the above bridge circuit). Accordingly, when the potentials of the above signals e and f are low and high, as indicated by symbols "L" and "H", respectively, the P channel type MOS transistors T₁₁ and T₁₂ are turned-ON and the other pair of transistors T₁₃ and T₁₄ are turned-OFF. Therefore, the potential of the connecting point of the transistors T₁₁ and T₁₉ is pulled up to V CC level (e.g., 0 volt) by a charging current i flowing through the turned-ON transistor T₁₁ and the stray capacity, and conversely, the potential of the connecting point of the transistors T₁₃ and T₂₀ is pulled down to V EE level (e.g., -5.2 volts) by a discharging current i t flowing from the charged stray capacity through the turned-ON transistor T₁₂. As a result, the N channel type MOS transistors T₁₉ and T₂₀ constituting the flip-flop circuit are turned-OFF and turned-ON, respectively, and thus the above pulled-up and pulled-down potentials of the respective connecting points are latched as they are. Accordingly, the potential of the signal g output from the connecting point of the transistors T₁₁ and T₁₉ is maintained at a high level (e.g., 0 volt), the potential of the signal j output from the connecting point of the transistors T₁₃ and T₂₀ is maintained at a low level (e.g., -5.2 volts), and the above signal g and the signal j complementary to the signal g are supplied from the level converter to the decoder circuit constituted by MOS transistors. In the above case, it is assumed that the potentials of the signals e and f are low and high, respectively. But when the potentials of the signals e and f are high and low, respectively, the pair of transistors T₁₃ and T₁₄ are turned-ON, and conversely, the pair of transistors T₁₁ and T₁₂ are turned-OFF, and thus the transistors T₁₉ and T₂₀ are turned-ON and turned-OFF, respectively. Accordingly, the potentials of the signals g and j are changed to low level and high level, respectively. Namely, the potentials of the signals g and j output from the level converter 12′ are changed (i.e., inverted) in accordance with not only the potential level of the input address bit signal A₀ but also the potential levels of the signals R and R supplied from the circuit 13′. Figure 2B is a circuit diagram illustrating an example of the above circuit 13′ for supplying the signals R and R to the bases of the pair of bipolar transistors T₆ and T₇. In the circuit 13′ shown in Fig. 2B, reference symbol PROM is a diode for programming predetermined data, and is generally constituted from a bipolar transistor. Although the circuit including the PROM is usually open, if a predetermined potential is applied through the terminals (pads) T₁ and T₂ and a current having a predetermined value flows against the PN junction formed in the diode, the PN junction is caused to self-destruct, and as a result, a short-circuit is formed between the terminals T₁ and T₂ , and thus predetermined data is programmed. When the circuit including the PROM is open (i.e., when the above short-circuit is not formed across the resistor R₆), the potential drop due to the current flowing through the resistors R₅ and R₆ is made larger than that due to the current flowing through the resistor R₇ , and thus the potential supplied to the base of the bipolar transistor T₂₁ is made lower than that supplied to the base of the bipolar transistor T₂₂. Accordingly, the potential of the signal R output from the emitter of the transistor T₂₁ becomes low level, but the potential of the signal R output from the emitter of the transistor T₂₂ becomes high level. Conversely, when the above short-circuit is formed by the destruction of the above PN junction of the PROM (i.e., when the short-circuit is formed in parallel with the resistor R₆), the potential drop due to the current flowing through the resistor R₅ is made smaller than that due to the current flowing through the resistor R₇ , and thus the potential supplied to the base of the transistor T₂₁ is made higher than that supplied to the base of the transistor T₂₂. Accordingly, the potential of the signal R output from the emitter of the transistor T₂₁ becomes high level but the potential of the signal R output from the emitter of the transistor T₂₂ becomes low level. In this connection, reference characters I₅ to I₈ show constant current sources. Therefore, the potentials of the signals R and R output from the circuit 13′ are changed (i.e., inverted) in accordance with data programmed in the PROM. As above-mentioned, in the above circuit as shown in Fig. 2A, a circuit configuration constituted by emitter coupled logic gates connected in series and to which both the corresponding address bit signal and the signals R and R , corresponding to a data stored in the PROM provided in the circuit 13′, are input, respectively, is adopted as the address buffer circuit. But, in an address buffer circuit constituted by the emitter coupled logic gates connected in series, problems arise in that a margin for the power supply potential applied to the address buffer circuit is reduced, and thus it is impossible to obtain a sufficient logic amplitude (i.e., a sufficient potential difference between high and low levels) for the signals output from the address buffer circuit, and accordingly, the speed of the operation of the level converter connected to the address buffer circuit is reduced. It is desirable to increase the margin for the power supply potential applied to the address buffer circuit and to lower the low potential level of the signals supplied from the address buffer circuit to the level converter (e.g., to lower this level from -2.4 volts as shown in the above conventional circuit to, for example, -3.2 volts), and thus to increase the level conversion speed of the level converter by constituting the level converter as a circuit configuration such that the inversion or non-inversion of the address bit signal, based on the above signals R and R can be controlled within the level converter, and accordingly, the address buffer circuit can be constructed as a usual current switch including only the emitter coupled logic gate to which the address bit signal is input (i.e., not including the emitter coupled logic gate to which the above signals R and R are input). Figure 3 is a circuit diagram illustrating an example of the circuit corresponding to the above portion 1-0, in an embodiment of the invention. The same reference numerals or characters as in Fig. 2A are given to each of the corresponding circuit portions shown in Fig. 3. In Fig. 3, reference numeral 11 shows an ECL type address buffer circuit constructed as a usual current switch, to which the address bit signal A₀ and the reference signal V ref are input. Reference numeral 13 denotes a circuit for controlling the inversion or non-inversion of the address bit signal in accordance with data stored in the above circuit 13 (e.g., the logic level of a row address bit corresponding to a portion of a standard memory cell array, which includes a defective memory cell therein). The control signals output from terminals a and b of the circuit 13, which signals are complementary to each other, are supplied to input terminals a and b of complementary MOS inverter circuits, as mentioned below, respectively. Reference numeral 12 shows a level converter for an embodiment of the invention. The level converter 12 comprises P channel type MOS transistors T₁₁ to T₁₄ constituting the bridge circuit and N channel type MOS transistors T₁₉ and T₂₀ constituting the flip-flop circuit as shown in Fig. 2A, and a pair of complementary MOS (CMOS) inverter circuits for supplying the power source potential V CC or V EE to a connection point c (i.e., the connection point between the transistors T₁₁ and T₁₃) and a connection point d (i.e., the connection point between the transistors T₁₂ and T₁₄) in the bridge circuit, respectively, in accordance with the potential levels of the control signals supplied from the above circuit 13. Namely, one of the above CMOS inverter circuits comprises a P channel type MOS transistor T₁₅ and a N channel type MOS transistor T₁₆ , each having a gate to which the control signal is supplied from the terminal a of the circuit 13, and supplies the power source potentials V CC or V EE to the connecting point c in accordance with the potential level of the control signal supplied from the terminal a . The other CMOS inverter circuit comprises a P channel type MOS transistor T₁₇ and an N channel type MOS transistor T₁₈ each having a gate to which the control signal is supplied from the terminal b of the circuit 13, and supplies the power source potentials V CC or V EE to the connecting point d in accordance with the potential level of the control signal supplied from the terminal b . As shown in Fig. 3, the connecting points (nodes) c and d are positioned alternately among the four connecting points provided in the bridge circuit constituted by the transistors T₁₁ to T₁₄. In this connection, the size of each of the transistors T₁₅ to T₁₈ constituting the above CMOS inverter circuits is large enough that the resistance value when turned-ON can be neglected. As a result, a circuit can be realized whereby the power source potentials V CC and V EE are substantially directly supplied to the connecting points c and d , respectively (as shown in Fig. 4A), or the power source potentials V EE and V CC are substantially directly supplied to the connecting points c and d , respectively (as shown in Fig. 4B), in accordance with the potential levels of the control signals supplied to the input terminals a and b of the CMOS inverter circuits. Namely, the power source potentials applied to the connecting points c and d may be changed from V CC to V EE , and vice versa, in accordance with the potential levels of the control signals supplied to the input terminals a and b of the CMOS inverter circuits, as shown in Fig. 4A and Fig. 4B. The circuit 13 for controlling the inversion or non-inversion of the address bit signal comprises a data storing portion (ROM portion) M constituted by, for example, a polysilicon layer which may be disconnected by laser, a fuse which may be disconnected by a predetermined current, or the above PROM constituted by a diode. The data (e.g., the logic level of a row address bit corresponding to a portion of a standard memory cell array which includes a defective memory cell) is stored in the portion M by selecting whether the circuit including the portion M is connected or disconnected. Therefore, where the circuit including the ROM portion M is connected, the potential level of the connecting point between a resistor R₃ and gates of the P channel type MOS transistor T₂₁ and N channel type MOS transistor T₂₂ is made high level, and thus the transistor T₂₁ is turned-OFF and the transistor T₂₂ is turned-ON. As a result, the potential of the control signal output from the terminal a is set to a low level, as indicated by the symbol "L", and the low level signal is supplied to gates of the P channel type MOS transistor T₂₃ and N channel type MOS transistor T₂₄ , and thus the transistor T₂₃ is turned-ON and the transistor T₂₄ is turned-OFF. As a result, the potential of the control signal output from the terminal b is set to a high level, as indicated by the symbol "H", being thus inverted relative to the level at a . Accordingly, in the level converter 12, the P channel type transistor T₁₅ is turned-ON by the above low level signal supplied from the terminal a , and thus the high level potential V CC is supplied through the turned-ON transistor T₁₅ to the connecting point c . Also, the N channel type transistor T₁₈ is turned-ON by the above high level signal supplied from the terminal b , and accordingly, the low level potential V EE is supplied through the turned-ON transistor T₁₈ to the connecting point d , and thus the circuit configuration of the level converter 12 is equivalent to that shown in Fig. 4A. Under the above conditions, if the potential level of the address bit signal A₀ supplied to the base of the NPN transistor T₁ is high (e.g., -0.8 volts), the transistor T₂ connected at the base to the emitter of the transistor T₁ is turned-ON, and the transistor T₃ , to the base of which the reference signal V ref is supplied, is turned-OFF. As a result, the base potential of the transistor T₄ becomes low level due to the voltage drop produced between the resistor R₁ , and thus the potential level of the signal e supplied from the emitter of the transistor T₄ to the gates of a pair of MOS transistor T₁₁ and T₁₂ becomes low level (e.g., -3.2 volts). On the other hand, the base potential of the transistor T₅ becomes high level (V CC level), and thus the potential level of the signal f supplied from the emitter of the transistor T₅ to the gates of the other pair of MOS transistors T₁₃ and T₁₄ becomes high level (e.g., -0.8 volts). As a result, the pair of MOS transistors T₁₁ and T₁₂ are turned-ON but the other pair of MOS transistors T₁₃ and T₁₄ are turned-OFF. Therefore, the potential level of the signal g output from the connecting point between the turned-ON transistor T₁₁ and turned-OFF transistor T₁₉ becomes high level (V CC level, e.g., 0 volt), and the potential level of the signal j output from the connecting point between the turned-ON transistors T₁₂ and T₂₀ becomes low level (V EE level, e.g., -5.2 volts). These signals g and j are then supplied from the level converter to the decoder circuit constituted by MOS transistors. In this connection, if the potential level of the address bit signal A₀ supplied to the base of the transistor T₁ is low (e.g., -1.6 volts) the transistor T₂ is turned-OFF and the transistor T₃ is turned-ON, and as a result, the potential level of the signal e becomes high level but. the potential level of the signal f becomes low level. Accordingly, the pair of MOS transistors T₁₁ and T₁₂ are turned-OFF but the other pair of MOS transistors T₁₃ and T₁₄ are turned-ON, and thus the potential levels of the signals g and j become low and high, respectively. Namely, the potential levels of the signals g and j output from the level converter are changed (i.e., inverted) in accordance with the potential level of the address bit signal supplied through the address buffer circuit to the level converter. Also, where the circuit including the ROM portion M is disconnected, the potential levels of the control signals supplied from the terminals a and b become high and low, respectively. Accordingly, in the level converter 12, the N channel type transistor T₁₆ is turned-ON by the above high level signal supplied from the terminal a , and thus the low level potential V EE is supplied through the turned-ON transistor T₁₆ to the connecting point c . Also, the P channel type transistor T₁₇ is turned-ON by the above low level signal supplied from the terminal b , and thus the high level potential V CC is supplied through the turned-ON transistor T₁₇ to the connecting point d . Accordingly, the circuit configuration of the level converter 12 becomes equivalent to that shown in Fig. 4B. Therefore, even if the potential level of the address bit signal A₀ supplied to the base of the transistor T₁ is high and the pair of MOS transistors T₁₁ and T₁₂ are turned-ON due to the low potential level of the signal e , the potential level of the signal g becomes low level (V EE level) and the potential level of the signal j becomes high level (V CC level), as shown in Fig. 4B. Therefore, the potential levels of the signals g and j output from the level converter are also changed (i.e., inverted), as shown in Fig. 4A and Fig. 4B, in accordance with the potential levels of the control signals supplied from the above circuit 13 to the level converter. In this connection, in Fig. 4A and 4B, reference symbol i corresponds to the charging current as described in Fig. 2A, and the flip-flop circuit comprising the N channel transistors T₁₉ and T₂₀ is driven by the above charging current. Also, reference symbol i t corresponds to the discharge current described in Fig. 2A, and the potential of the corresponding portion may be rapidly pulled down by the above discharge current. As above-mentioned, by using the level converter 12 according to the present invention, the potential levels of the signals output from the level converter 12 may be changed (i.e., inverted) within the level converter 12, in accordance with the potential levels of the control signals supplied from the circuit 13 for controlling an inversion or non-inversion of the address bit signal according to the data stored therein. Namely, by using the level converter 12 according to this embodiment of the invention, it is not necessary to provide the address buffer circuit including the emitter coupled logic gates connected in series, to which gates both the address bit signal and the control signals R and R output from the circuit 13, are supplied, as shown in Fig. 2A. Therefore, the address buffer circuit 11 connected to this level converter 12 may be constructed as a usual current switch to which only the address bit signal and the reference signal are input. Although, in the above embodiment, P channel type MOS transistors T₁₁ and T₁₄ and N channel type MOS transistors T₁₉ and T₂₀ are adopted as the four MOS transistors constituting the bridge circuit and the two MOS transistors constituting the flip-flop circuit, respectively, it is also possible to use N channel type MOS transistors for T₁₁ to T₁₄ and P channel type MOS transistors for T₁₉ and T₂₀ , if the address buffer circuit is constituted by PNP type bipolar transistors instead of NPN type bipolar transistors constituting ECL gates as shown in Fig. 3. As above-mentioned, in an embodiment of the present invention, it is possible to increase the margin for the power supply potential applied to the address buffer circuit and to increase the logic amplitude (i.e. the potential difference between high level and low level) of the signals supplied from the address buffer circuit to the level converter (e.g. to lower the low potential level to -3.2 volts), and thus obtain a high operational speed of the level converter, as compared with a semiconductor memory device having a level converter but not in accordance with the present invention.

Claims: A level converter in a semiconductor memory device, comprising a bridge circuit having a first MOS transistor (T₁₁) which is connected through a first node ( c ) of the circuit to a second MOS transistor (T₁₃) which is connected through a second node (j) of the circuit to a third MOS transistor (T₁₂) which is connected through a third node ( d ) of the circuit to a fourth MOS transistor (T₁₄) which is connected through a fourth node (g) of the circuit to the said first MOS transistor (T₁₁), the four MOS transistors all being of the same conductivity type, respective gate electrodes of the first and third MOS transistors (T₁₁, T₁₂) being connected to receive a first input signal ( e ) from addressing circuitry (11) of the device, respective gate electrodes of the second and fourth MOS transistors (T₁₃, T₁₄) being connected to receive from the addressing circuitry an input signal ( f ) complementary to the said first input signal, and the said second and fourth nodes being connected to deliver respective mutually-complementary output signals ( g , j ) of the level converter to a subsequent stage of the device; characterised in that the said first and third nodes ( c , d ) are connected to receive respective mutually-complementary voltage signals determined by control circuitry (13) of the device. A level converter as claimed in claim 1, further including two CMOS inverter circuits (T₁₅,T₁₆;T₁₇,T₁₈) the respective inputs of which are connected to the said control circuitry (13) for receiving therefrom respective mutually-complementary control signals ( a , b ) and the respective outputs of which are connected respectively to the said first and third nodes ( c , d ) for applying thereto the said mutually-complementary voltage signals. A level converter as claimed in claim 1 or 2, further including a flip-flop circuit (T₁₉,T₂₀) connected to the said second and fourth nodes for latching the said mutually-complementary output signals ( g , j ). A level converter as claimed in claim 3, wherein the said flip-flop circuit (T₁₉,T₂₀) comprises a pair of MOS transistors of the opposite conductivity type to that of the said four MOS transistors (T₁₁-T₁₄) of the bridge circuit, respective gates of the MOS transistors (T₁₉, T₂₀) of the pair being connected to the said second and fourth nodes respectively. A semiconductor memory device including a plurality of level converters (12), each as claimed in any preceding claim, and also including a plurality of address buffer circuits (11) associated respectively with the level converters, each of the address buffer circuits being constituted by ECL gates and receiving at its inputs one of a plurality of address bit signals (A₀,A₁,....A n ) and a reference signal (V ref ) and providing at its outputs the said first input signal ( e ) and the said complementary input signal ( f ) for its associated level converter (12), the potential levels of those two input signals ( e , f ) being changed by the address buffer circuit in dependence upon the potential of the address bit signal (A₀,A₁....A n ) received thereby. A device as claimed in claim 5, wherein each level converter is as claimed in claim 2, and the control circuitry includes a plurality of individual control circuits (13) connected respectively with the level converters (12) for applying thereto the said mutually-complementary control signals ( a , b ), the respective potential levels of the control signals ( a , b ) applied to each level converter being changed in dependence upon data stored in the individual control circuit (13) concerned. A device as claimed in claim 6, further including: a standard memory cell array (5); a redundancy memory cell array (6); a decoder circuit (2) connected to the said level converters (12) for receiving the mutually-complementary output signals ( g , j ) of each converter; and a switching control circuit (7) for controlling a switch from the standard memory cell array to the redundancy memory cell array such that when each of the address bit signals (A₀,A₁...A n ) coincides with the data stored in the corresponding individual control circuit (13) the redundancy memory cell array (6) is selected for reading/writing, whereas when any one of the address bit signals does not so coincide the decoder circuit (2) is operable, in dependence upon the said mutually-complementary output signals ( g , j ) of the level converters (12), to select for reading/writing the memory cell of the standard memory cell array (5) having the address indicated by the said address bit signals.

Inventors: FUKUSHI ISAO VIRA HAKURAKU -GO, FUKUSHI, ISAO VIRA HAKURAKU 25-GO, 13-47
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1988
Main classification: G11C8
IPC codes: G11C8, H03K19, G11C11, H03K3, H03K5