Transfer Circuit for Signal Lines

1. Field of the Invention

The present invention relates to a transfer circuit for signal lines and utilized, for example, for selectively transferring one of a plurality of local data buses to a common data bus.

2. Description of the Related Art

In a static random access memory (SRAM), a memory cell array is divided into a plurality of blocks, to obtain a low power consumption or a high speed processing. In this case, one of a plurality of local buses connected to the memory cell array block must be selected and the data thereon transferred to a common data bus. This selection and transfer are carried out by a transfer gate circuit.

In a transfer circuit for signal lines using a transfer gate, since all of the transistors are MIS (metal insulator semiconductor) transistors, the resistance in a conductive state is relatively high, the overdrive voltage is low, and the local data bus has a large electrostatic capacity due to the connection of many memory cells. Therefore, a time constant for a charge in the bus is long, and a problem arises in that it takes a long time to transfer data from the local data bus to the common data bus.

The present invention is intended to provide a high speed transfer circuit for signal lines by using a bipolar transistor and MIS transistors.

An object of the present invention is to provide a high speed operating transfer circuit for signal lines.

According to the present invention, there is provided a transfer circuit for controlling a signal transfer between a first signal line and a second signal line in response to a control signal comprising a first MIS transistor including a first electrode connected to the first signal line, a second electrode, and a gate electrode; a second MIS transistor including a first electrode connected to the second electrode of the first MIS transistor, a second electrode connected to the second signal line, and a gate electrode; and a bipolar transistor including a base electrode connected to the first signal line, a first electrode connected to a power supply line, and a second electrode connected to the first electrode of the second MIS transistor; the gate electrodes of the first MIS transistor and the second MIS transistor being controlled in response to the control signal such that the first MIS transistor and the second MIS transistor operate in a complementary manner.

Other features and advantages of the invention will be apparent from the following description given with reference to the accompanying drawings.

FIG. 1 is a partial circuit diagram of a static random access memory, explaining an application example of a transfer circuit for signal lines;

FIG. 2 is a partial circuit diagram of a static random access memory, explaining a conventional transfer circuit for signal lines;

FIG. 3 is a partial circuit diagram of a static random access memory, explaining a transfer circuit for signal lines according to a first embodiment of the invention;

FIG. 4 is a circuit diagram of a transfer circuit for signal lines according to a second embodiment of the present invention;

FIG. 5 is a circuit diagram of a transfer circuit for signal lines according to a third embodiment of the present invention;

FIG. 6 is a circuit diagram of a transfer circuit for signal lines according to a fourth embodiment of the present invention; and

FIG. 7 is a waveform diagram in the transfer circuit for the signal lines shown in FIG. 3.

Prior to an explanation of embodiments of the present invention, a static random access memory (SRAM) wherein transfer circuits for signal lines are applied is explained with reference to FIG. 1.

In FIG. 1, blocks BLK.sub.1 and BLK.sub.2 enclosed by broken lines are divided into memory cell array blocks (shown as a partially abbreviated diagram). Each block comprises memory cells (MC's) as memory elements, and in each block, one column is selected by column selection circuits controlled by signals CA.sub.0 to CA.sub.n from a decoder, and one word line (WL.sub.0 to WL.sub.m) is selected by the decoder. Then, data is read from an MC arranged at a cross point of the word line and a pair of bit lines (e.g. one pair of BL.sub.0, to BL.sub.0 ; to BL.sub.n, BL.sub.n) selected by the column selection circuit, and the data is supplied to a common data bus (DB, DB) through a local data bus (e.g. one pair of DB.sub.1, DB.sub.1 ; DB.sub.2, DB.sub.2 ; etc.). The common data bus is connected to a sense amplifier SA and the data is output as D.sub.out through an data output buffer OB. Here, a transfer circuit for signal lines must be provided to selectively connect the plurality of local data buses and the common data bus. In FIG. 1, the transfer circuit for signal lines comprises transistors Q.sub.21, Q.sub.22, Q.sub.31, and Q.sub.32, which are controlled by a signal BS.sub.1 or BS.sub.2.

Write data (D.sub.in) for this SRAM is supplied to write amplifiers (WRITE AMP 1 and 2) through a data-in buffer (DATA-IN BUF) and data bus (DBW, DBW). One memory cell array block is selected by the selection of a write amplifier controlled by a control signal (WS.sub.1 or WS.sub.2) and the data is supplied to the selected MC through the local data bus.

The conventional transfer circuit for signal lines is explained with reference to FIG. 2. FIG. 2 shows a portion of the SRAM in FIG. 1 in detail. In FIG. 2, the same elements as in FIG. 1 are denoted by the same reference characters. Data from each MC is supplied to local data buses (DB.sub.1, DB.sub.1 ; DB.sub.2, DB.sub.2) through a transfer gate circuit TG.sub.B, which comprises transistors Q.sub.11 and Q.sub.12, and one of the transfer gate circuits (TG.sub.1, TG.sub.2) is selected by a block selection control signal (BS.sub.1 or BS.sub.2) and is made conductive to the common data bus as a transfer circuit for signal line. The TG.sub.1 comprises MIS transistors Q.sub.21 and Q.sub.22, and each transistor is made conductive by the block selection control signal BS.sub.1. MIS transistors Q.sub.23 and Q.sub.24 are used to apply a voltage, e.g., Vcc (5 volts), through an effective resistance, so that a floating state thereof does not exist when the local bus is at the nonselection state. The transfer gate TG.sub. 2 comprises MIS transistors Q.sub.31 and Q.sub.32, the power source voltage Vcc is connected to the local data bus (DB.sub.2, DB.sub.2) through MIS transistors Q.sub.33 and Q.sub.34, and the operation thereof is the same as that of the TG.sub.1. In the conventional transfer circuit for signal lines, since the resistance of the MIS transistors Q.sub.21, Q.sub.22, Q.sub.31, and Q.sub.32 does not become completely zero in the conductive state thereof, the memory cell having a small power supply capacity cannot charge the common data bus with a large amount of electric current in a short time, and thus the bus transfer time cannot be shortened.

A transfer circuit for signal lines according to a first embodiment of the invention is explained with reference to FIG. 3. Note, in FIG. 3, a portion of the SRAM is abbreviated as in FIG. 2.

A memory cell is a memory element in the SRAM as shown in FIGS. 1 and 2 and is a flip-flop circuit shown at the top of FIG. 3. The memory cell, for example, comprises four MIS transistors and two resistors, and two series-connected resistors and transistors are arranged in parallel between the power source and ground. A drain of one of the transistors is cross-connected to a gate of another transistor, and vice versa. The gate of each transistor is connected to a MIS transistor to be selected by a word line (WL) and to be connected to a respective bit line. A pair of bit lines (BL.sub.0, BL.sub.0) is connected to a local data bus (DB.sub.1, DB.sub.1) through a transfer gate circuit TG.sub.B, which comprises transistors Q.sub.11 and Q.sub.12 as a column selection circuit. Another pair of bit lines from another memory cell array block is connected to a local data bus (e.g. DB.sub.2 , DB.sub.2) in the same way. The local data bus (DB.sub.1, DB.sub.1) is connected to the common data bus through a transfer gate circuit TG.sub.11, according to the first embodiment of the invention, and a selection signal BS.sub.1 makes the transfer gate circuit conductive or disconnects same. The local data bus (DB.sub.2, DB.sub.2) and the local data bus belonging to other blocks are connected and controlled in the same way.

In the following description, the transfer gate circuit TG.sub.11 (transfer circuit assembly) is explained. The TG.sub.11 comprises a symmetrical circuit for transmitting a complementary pair of signals. Here, only a half of the symmetrical circuit is explained, but the other half thereof is exactly the same.

The half circuit comprises a bipolar transistor (QB.sub.11 or QB.sub.12 ), an n channel MIS transistor (QN.sub.31 or QN.sub.32), and a p channel MIS transistor (QP.sub.33 or QP.sub.34). one of the local data bus signal lines DB.sub.1 is connected to a base of the NPN type bipolar transistor QB.sub.11 ; a collector of the transistor QB.sub.11 is connected to the power source Vcc; a source of the transistor QN.sub.31 is connected to a source of the transistor QP.sub.33 ; a gate of the transistor QN.sub.31 is connected to a gate of the transistor QP.sub.33 ; a drain of the transistor QN.sub.31 is connected to the base of the transistor QN.sub.11 ; and, a drain of the transistor QP.sub.33 is connected to the common data bus DB. For another signal line DB.sub.1 of the local data bus, the transistor QB.sub.11 is replaced by the transistor QB.sub.12, the transistor QN.sub.31 is replaced by the transistor QN.sub.32, the transistor QP.sub.33 is replaced by the transistor QP.sub.34, and the drain of the transistor QP.sub.34 is connected to the common data bus DB. The remaining circuit constitution of the another signal line of the local data bus is the same as that of one of the local data bus signal lines. Note, the interconnected MIS transistor gates are supplied with the selection signal BS.sub.1 .

Also, the above-mentioned circuit constitution is applied to the transfer gate circuit TG.sub.12 to which the local data bus (DB.sub.2, DB.sub.2) is connected, as for TG.sub.11.

If the line to be transferred is not complementary to a bus line but is an individual line, a half circuit application in the symmetrical circuit is sufficient.

An operation of this circuit of the first embodiment is now explained. When data is transferred from the local data bus to the common data bus, the selection signal BS.sub.1 is at a "low" level, the n channel MIS transistors QN.sub.31 and QN.sub.32 are OFF, and the p channel MIS transistors QP.sub.33 and QP.sub.34 are ON (conductive). The data signal on the local data bus DB.sub.1 is applied to the base of the transistor QB.sub.11, the current is amplified, and the data is transferred to the common data bus DB instantly through the emitter of the transistor QB.sub.11 and the transistor QP.sub.33. Similarly, a data signal on the local data bus DB.sub.1 is applied to the base of the transistor QB.sub.12, the current is amplified, and the data is transferred to the common data bus DB instantly through the emitter of the transistor QB.sub.12 and the transistor QP.sub.34.

When the data transfer is inhibited, the selection signal BS.sub.1 is at a high level, the n channel transistors QN.sub.31 and QN.sub.32 are ON, and the p channel transistors QP.sub.33 and QP.sub.34 are OFF. Accordingly, the transistor QB.sub.11 and QB.sub.12 are made OFF by a short circuit between the base and emitter thereof, and thus the data signals from the local data bus (DB.sub.1, DB.sub.1) are completely disconnected.

In the above operation, since the transistor QN.sub.31 is short circuited during the non-selection time, delay of the conductive operation at the next step is prevented due to the absence of an emitter voltage higher than the base voltage in the transistor QB.sub.11. The bipolar transistor QB.sub.11 amplifies the signal current from the MC by using an emitter follower, the transistor QP.sub.33 supplies the electric current from the transistor QB.sub.11 to the common data bus DB when the transfer circuit for signal lines is in a selection state, and the transistor QP.sub.33 disconnects the signal from the MC so that the signal from the bus DB.sub.1 does not reach the bus DB when the transfer circuit is in a non-selection state.

The common data bus is connected to a sense amplifier SA, and the data is output through an output buffer circuit. A pull-down circuit PD is connected to the common data bus. This circuit PD comprises two MIS transistors Q.sub.15 and Q.sub.16, and a drain of the transistor Q.sub.15 is connected to the common data bus DB and a drain of the transistor Q.sub.16 is connected to the common data bus DB. Sources of the transistors Q.sub.15 and Q.sub.16 are grounded and bases of the transistors Q.sub.15 and Q.sub.16 are connected to the power source V.sub.1 or Vcc. The circuit PD, lowers the bus voltage when the voltage of the common data bus is changed from high to low. The channel widths of the transistors Q.sub.15 and Q.sub.16 are made narrower than that of the MIS transistor QP.sub.33 or the like.

Assuming that the voltage levels of connecting points between the sources of the transistors QN.sub.31 and QP.sub.33 and between the sources of the transistors Q.sub.32 and QP.sub.34 are A and B, respectively, as shown in FIG. 3, the voltage levels of the connecting points, of the local data bus (DB.sub.2, DB.sub.2) and of the common data bus (DB, DB) are as shown in FIG. 7. The waveforms in FIG. 7 are generated when a high level of the selection signal is transferred from BS.sub.2 to BS.sub.1. In FIG. 7, the axis of the ordinates shows a voltage (volt) and the quadrature axis shows the time (t).

When using the above-mentioned circuit, since the current of the data signal through the local data bus is amplified, the common data bus is charged by a large amount of electric current, and thus the transfer time for the data becomes very short and a high speed transfer is possible.

A circuit diagram of a transfer circuit for signal lines according to a second embodiment of the invention is shown in FIG. 4. This circuit comprises two NPN type bipolar transistors QB.sub.11 and QBV.sub.12, two p channel MIS transistors QP.sub.41 and QP.sub.42, and two n channel MIS transistor and QN.sub.43 and QN.sub.44.

The local data bus DB.sub.1 is connected to the base of the transistor QB.sub.11 and a drain of the transistor QP.sub.41, and the collector of the transistor QB.sub.11 is connected to the power source Vcc. Sources of the transistors QP.sub.41 and QN.sub.43 are interconnected and the connecting point is connected to the emitter of the transistor QB.sub.11, and a drain of transistor QN.sub.43 is connected to the common data bus DB. Gates of the transistors QP.sub.41 and QN.sub.43 are interconnected and are applied with a selection signal BS.

The local data bus DB.sub.1 is connected to the base of the transistor QB.sub.12 and a drain of the transistor QPO.sub.42, the collector of the transistor QB.sub.12 is connected to the power source Vcc, sources of the transistors QP.sub.42 and Qn.sub.44 are interconnected and the connecting point is connected to the emitter of the transistor QB.sub.12, and a drain of the transistor QN.sub.44 is connected to the common data bus DB. Gates of the transistors QP.sub.42 and QN.sub.44 are interconnected and are applied with a selection signal BS. In this circuit, during the selection (i.e. the signal BS is high level), the transistors QP.sub.41 and QP.sub.42 are OFF and the transistors QN.sub.43 and QN.sub.44 are ON. The operation of this circuit is the same as that of the first embodiment.

A circuit diagram of a transfer circuit for signal lines according to a third embodiment of the invention is shown in FIG. 5. This circuit comprises two NPN type bipolar transistors QB.sub.11 and QB.sub.12 and four n channel MIS transistors QN.sub.51, QN.sub.52, QN.sub.53, and QN.sub.54.

The local data bus DB.sub.1 is connected to the base of the transistor QB.sub.11 and a drain of the transistor QN.sub.51, the collector of the transistor QB.sub.11 is connected to the power source Vcc, sources of the transistors QN.sub.51 and QN.sub.53 are interconnected and the connecting point is connected to the emitter of the transistor QB.sub.11, and a drain of the transistor QN.sub.53 is connected to the common data bus DB. A gate of the transistors QN.sub.51 is supplied with the signal BS, and a gate of the transistor QN.sub.53 is supplied with the signal BS (inverted BSsignal).

The local data bus DB.sub.1 is connected to the base of the transistor QB.sub.12 and a drain of the transistor QN.sub.52, the collector of the transistor QB.sub.12 is connected to the power source Vcc, sources of the transistors QN.sub.52 and Qn.sub.54 are interconnected and the connecting point is connected to the emitter of the transistor QB.sub.12, and a drain of the transistor QN.sub.54 is connected to the common data bus DB. A gate of the transistor QN.sub.52 is supplied with the selection signal BS and a gate of the transistor QN.sub.54 is supplied with the selection signal BS. In this circuit, during the transfer State (i.e. the signal BS is high and the signal BS is low level), the transistors QN.sub.51 and QN.sub.52 are OFF and the transistors QN.sub.53 and QN.sub.54 are ON. The operation of this circuit is the same as that of the first embodiment.

A circuit diagram of a transfer circuit for signal lines according to a fourth embodiment of the invention is shown in FIG. 6. This circuit comprises two NPN type bipolar transistors QB.sub.11 and QB.sub.12 and four p channel MIS transistors QP.sub.61, QP.sub.62, QP.sub.63, and QP.sub.64.

The local data bus DB.sub.1 is connected to the base of the transistor QB.sub.11 and a drain of the transistor QP.sub.61, the collector of the transistor QB.sub.11 is connected o the power source Vcc, sources of the transistors QP.sub.61 and QP.sub.63 are interconnected and the connecting point is connected to the emitter of the transistor QB.sub.11, and a drain of the transistor QP.sub.63 is connected to the common data bus DB. A gate of the transistor QP.sub.61 is supplied with the selection signal BS, and a gate of the transistor QP.sub.63 is supplied with the selection signal BS.

The local data bus DB.sub.1 is connected to the base of the transistor QB.sub.12 and a drain of the transistor QP.sub.62, the collector of the transistor QB.sub.12 is connected to the power source Vcc, sources of the transistors QP.sub.62 and QP.sub.64 are interconnected and the connecting point is connected to the emitter of the transistor QB.sub.12, and a drain of the transistor QP.sub.64 is connected to the common data bus DB. A gate of the transistor QP.sub.62 is supplied with the selection signal BS and a gate of the transistor QP.sub.64 is supplied with the selection signal BS. In this circuit, during the transfer state the transistors QP.sub.61 and QP.sub.62 are OFF and the transistors QP.sub.63 and QP.sub.64 are ON. The operation of this circuit is the same as that of the first embodiment.

In the above-mentioned description of the embodiments, a pair of transfer circuits is used with transfer buses supplied with a pair of complementary signals, but this transfer circuit for signal lines can function using only one of the pair of circuits, to transfer data from one signal line to another signal line.