# Patent

## Title
Serial access memory

## Abstract

A serial access memory low in current consumption, capable of restraining an increase in a chip size even if memory capacity increases. The serial access memory has a first and a second memory arrays each having memory cells electrically connected to corresponding bit lines, signal lines provided in common between the memory arrays and electrically connected to the corresponding bit lines through first transfer circuits, write registers electrically connected to the corresponding signal lines through a second transfer circuit, a write bus electrically connected to the write registers through a third transfer circuit, an input circuit electrically connected to the write bus, read registers electrically connected to the corresponding signal lines through a fourth transfer circuit, a read bus electrically connected to the read registers through a fifth transfer circuit, and an input circuit electrically connected to the read bus.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This is a divisional application of application Ser. No. 10/259,598, filed Sep. 30, 2002, now U.S. Pat. No. 6.674,683, which is a divisional application of Ser. No. 09/962,442, filed Sep. 26, 2001, now U.S. Pat. No. 6,608,794, which are hereby incorperated by reference in their entirety for all purposes.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a serial access memory, and particularly to transfer units set as paths used when data stored in memory cells are respectively transferred to read and write registers.
2. Description of the Related Art
Each of memory blocks of a serial access memory adopts a configuration wherein read registers and write registers are respectively added to memory cells of a DRAM. The memory capacity of such a memory block is normally taken up or configured in units of 256 Kbits or 512 Kbits, for example to ensure an operating margin for each memory and reduce the peak of current consumption. Since the serial access memory often deals with image data, it needs to have a capacity of a few Mbits. In order to implement it through the, use of the above memory block, the serial access memory is made up of a plurality of memory blocks.
With the recent scale-down technology, the memory cell can be formed greatly by shortening it. However, the read registers and write registers are not scaled down in a manner similar to the memory cells. Thus, although the occupied area of each memory cell in a memory block is reduced, the read registers and write registers are not so scaled down. Accordingly, a problem arises in that the serial access memory has not yet been scaled down in chip size as might be expected. Further, since the conventional serial access memory comprises the plurality of memory blocks including the write and read registers, circuits for controlling the respective registers and transfer units increase in number, thus increasing current consumption.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a serial access memory low in current consumption, which is capable of restraining an increase in chip size even if memory capacity increases.
A serial access memory of the present invention comprises first and second memory arrays. The first memory array includes first memory cells, first sense amplifiers and pairs of first bit lines connected to the first memory cells and the first sense amplifiers. The second memory array includes second memory cells, second sense amplifiers and second bit lines connected to the second memory cells and the second sense amplifiers. The serial memory further comprises pairs of column lines each of which is connected to one of the pairs of first bit lines and one of the pairs of the second bit lines, write registers each of which is connected to one of the pairs of column lines, a write address accessing circuit connected to the write registers for selecting one of said write registers, read registers each of which is connected to one of the pairs of column lines, a read address accessing circuit connected to the read registers for selecting one of the read registers, an input circuit connected to the write registers, and an output circuit connected to the write registers.



BRIEF DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:
FIGS. 1A-1B are a simplified circuit diagram showing a circuit of a principal part of a serial access memory according to a first embodiment of the present invention;
FIG. 2 is a timing chart for describing operating timings for the serial access memory according to the first embodiment of the present invention;
FIGS. 3A-3B are a simplified circuit diagram illustrating a circuit of a principal part of a serial access memory according to a second embodiment of the present invention;
FIG. 4 is a timing chart for describing operating timings for the serial access memory according to the second embodiment of the present invention;
FIGS. 5A-5C are a simplified circuit diagram depicting a circuit of a principal part of a serial access memory according to a third embodiment of the present invention;
FIG. 6 is a timing chart for describing operating timings for the serial access memory according to the third embodiment of the present invention;
FIGS. 7A-7B are a simplified circuit diagram showing a circuit of a principal part of a serial access memory according to a fourth embodiment of the present invention;
FIGS. 8A-8B are a simplified circuit diagram illustrating a circuit of a principal part of a serial access memory according to a fifth embodiment of the present invention;
FIGS. 9A-9B are a simplified circuit diagram depicting a circuit of a principal part of a serial access memory according to a sixth embodiment of the present invention;
FIGS. 10A-10B are a simplified circuit diagram showing a circuit of a principal part of a serial access memory according to a seventh embodiment of the present invention; and
FIGS. 11A-aaB are a simplified circuit diagram illustrating a circuit of a principal part of a serial access memory according to an eighth embodiment of the present invention.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will hereinafter be described in detail with reference to the accompanying drawings.
FIGS. 1A-1B are a simplified circuit diagram showing a circuit of a principal part of a serial access memory according to a first embodiment of the present invention. A configuration of the first embodiment will be explained below with reference to FIGS. 1A-1B.
The serial access memory according to the present embodiment comprises two memory blocks (corresponding to a memory block a and a memory block b). The memory blocks a and b have a plurality of memory cells respectively. The memory cells comprise memory cell transistors CTrija or CTrijb (where i=1 to m, j=1 to n, and m and n are whole numbers) and capacitors Cija or Cijb respectively. First ends of the capacitors Cija or Cijb are electrically connected to their corresponding first terminals of the memory cell transistors CTrija or CTrijb, whereas the other ends thereof are respectively electrically connected to a predetermined source or power supply (ground potential in the first embodiment).
Second terminals of the memory cell transistors CTrija or CTrijb are respectively electrically connected to bit lines BLia, /BLia, BLib or/BLib, and the gates thereof are respectively electrically connected to word lines WLja or WLjb.
As to the memory cell, for example, one connected to a pair of bit lines BLma and BLma/ is considered as one column unit. Each of sense amplifiers SAia is provided for each column unit. The sense amplifiers SAia or SAib are respectively electrically connected between each individual pairs of bit lines BLia and /BLia or between BLib and /BLib. These memory cells, sense amplifiers SAia or SAib, bit lines BLia, /BLia, BLib or /BLib and word lines WLja or WLib constitute either a memory cell array Ga or Gb. Incidentally, the word lines WLja or WLjb are electrically connected to either an X address accessing circuit Aa or Ab. The X address accessing circuit Aa (or Ab) selects only one word line WLja (or WLjb) from the word lines WLja (or WLjb) in response to an unillustrated address signal.
The bit lines pairs BLia and /BLia or BLib and /BLib set in column units are electrically connected to their corresponding pairs of signal lines CLi and /CLi which are parallel to the bit lines BLia, /BLia, BLib or /BLib and common to the memory blocks a and b through transfer circuit Ha or Hb. Either the transfer circuit Ha of the memory block a or the transfer circuit Hb of the memory block b comprises transfer transistor pairs Tri1a and Tri2a or Tri1b and Tri2b. These transfer transistors Tri1a, Tri2a, Tri1b or Tri2b have first terminals electrically connected to their corresponding bit lines BLia, /BLia, BLib or /BLib, second terminals electrically connected to their corresponding signal lines CLi and /CLi, and gates respectively commonly supplied with a transfer signal CTa or CTb.
Read registers RRi and write registers WRi are respectively electrically connected to both ends of the signal lines CLi and /CLi through transfer circuits I and F. The read registers RRi and write registers WRi respectively comprise two inverters whose inputs and outputs are respectively connected to one another. Further, the transfer circuits F and I respectively comprise transistor pairs Tri3 and Tri4 or Tri5 and Tri6. The transfer transistors Tri3 or Tri4 respectively have first terminals electrically connected to their corresponding write registers WRi, second terminals electrically connected to their corresponding signal lines CLi and /CLi, and gates commonly supplied with a write transfer signal WT. Further, the transfer transistors Tri5 or Tri6 respectively have first terminals electrically connected to their corresponding read registers RRi, second terminals electrically connected to their corresponding signal lines CLi and /CLi, and gates commonly supplied with a read transfer signal RT.
The write registers WRi are also respectively electrically connected to write data buses WD and /WD through a transfer circuit D. The transfer circuit D comprises transfer transistor pairs Tri1 and Tri2. First terminals of the transfer transistors Tri1 and Tri2 are respectively electrically connected to the write registers WRi, second terminals thereof are respectively electrically connected to the write data buses WD and /WD, and the gates thereof are respectively commonly supplied with address signals YWm. The address signals YWm are generated by a write address accessing circuit B. The write address accessing circuit B activates only one address signal YWm in response to an unillustrated address signal. Thus, data on the write data buses WD and /WD are read into the write registers WRi connected to the transfer transistor pairs Tri1 and Tri2 supplied with the activated address signal YWm, respectively.
An input circuit L is electrically connected to the write data buses WD and /WD. The input circuit L receives data DIN inputted from the outside therein and outputs it to the write data buses WD and /WD.
The read registers RRi are also electrically connected to read data buses RD and /RD through a transfer circuit K. The transfer circuit K comprises transfer transistor pairs Tri7 and Tri8. First terminals of the transfer transistors Tri7 and Tri8 are respectively electrically connected to the read registers RRi, second terminals thereof are respectively electrically connected to the read data buses RD and /RD, and the gates thereof are respectively commonly supplied with address signals YRm. The address signals YRm are generated by a read address accessing circuit C. The read address accessing circuit C activates only one address signal YRm in response to an unillustrated address signal. Thus, only data stored in the read registers RRi connected to the transfer transistor pairs Tri7 and Tri8 supplied with the activated address signal YRm are read into the read data buses RD and /RD, respectively.
An output circuit M is electrically connected to the read data buses RD and /RD. The output circuit M outputs the data outputted to the read data buses RD and /RD to the outside as output data DOUT.
FIG. 2 is a timing chart for describing timings provided to operate the serial access memory according to the first embodiment of the present invention. The operating timings for the serial access memory according to the first embodiment will be explained below using FIG. 2 according to times t1 through t9 shown in FIG. 2. Incidentally, an actual serial access memory is capable of performing a serial write operation and a serial read operation in asynchronous form perfectly except for a data transfer cycle. However, FIG. 2 shows a state in which serial write and read operations have been performed at different times to make it easy to understand their description.
FIG. 2 also shows a state in which only the memory block a is in operation. It is however needless to say that only the memory block b can be activated and the memory blocks a and b can be activated simultaneously.
<Time t1>
The input circuit L captures data DI1 from input data DIN and transfers it to the write data buses WD and /WD. The write address accessing circuit B selectively activates an address signal YW1. Thus, the transfer transistors Tr11 and Tr12 of the transfer circuit D are selectively turned on so that the write register WR1 is electrically connected to the write data buses WO and /WD. Accordingly, the data DI1 is written into the write register WR1.
<Time t2>
The input circuit L brings data D12 from the input data DIN and transfers it to the write data buses WD and /WD. The write address accessing circuit B selectively activates an address signal YW2. Thus, the transfer transistors Tr21 and Tr22 of the transfer circuit D are selectively turned on so that the write register WR2 is electrically connected to the write data buses WD and /WD. Accordingly, the data D12 is written into the write register WR2.
<Time T3>
The input circuit L takes in data Dim from the input data DIN and transfers it to the write data buses WD and /WD. The write address accessing circuit B selectively activates an address signal YWm. Thus, the transfer transistors Trm1 and Trm2 of the transfer circuit D are selectively turned on so that the write register WRm is electrically connected to the write data buses WD and /WD. Accordingly, the data DIm is written into the write register WRm.
<Time t4>
After the writing of the data into the write registers WRi has been completed, the written data DI1 through DIm are written into the memory array Ga at a time t4.
At first, the X address accessing unit Aa selects the corresponding word line WL1a (which is tentatively set as WL1a for explanation herein) and supplies a signal of a high level to the word line WL1a. Thus, the memory cell transistor CTri1a of the corresponding memory cell connected to the word line WL1a is turned on, so that the memory cell is brought to a selected state.
Since the write transfer signal WT is brought to a high level simultaneously, the transfer transistors Tri3 and Tri4 are turned on. Thus, the data written into the write registers WRi are temporarily transferred onto their corresponding signal lines CLi and /CLi through the transfer transistors Tri3 and Tri4.
After the data have fully been transferred to the signal lines CLi and /CLi, the transfer signal CTa is rendered high in level. Thus, the transfer transistors Tri1a and Tri2a of the transfer circuit Ha are turned on so that the signal lines CLi and /CLi are electrically connected to their corresponding bit lines BLia and /BLia. Accordingly, the data on the signal lines CLi and /CLi are temporarily transferred to the bit lines BLia and /BLia. The transferred data are respectively amplified by the sense amplifiers SAia and thereafter stored in their corresponding capacitors Ci1a of the memory cells (corresponding to the memory cells whose memory cell transistors CTri1a are kept on) connected to the word line WL1a. 
This series of operations is called “write transfer”.
<Time t5>
At a time t5, the data written into the corresponding memory cell is read out.
The X address accessing circuit Aa selects the corresponding word line WL1a (which is tentatively set as WL1a for explanation herein) and supplies a high level signal to the word line WL1a. Thus, the memory cell transistors CTri1a of the memory cells connected to the word line WL1a are turned on so that the data stored in the capacitors Ci1a of the memory cells are transferred to their corresponding bit lines pairs BLia and /BLia. The sense amplifiers SAia respectively amplify the data on the bit line pairs BLia and /BLia.
<Time t6>
Since the transfer signal CTa is rendered high in level, the transfer transistors Tri1a and Tri2a of the transfer circuit Ha are turned on so that the signal lines CLi and /CLi are electrically connected to their corresponding bit line pairs BLia and /BLia. Thus, the data on the bit line pairs BLia and /BLia, which have been amplified by the sense amplifiers SAia, are temporarily transferred onto the signal lines CLi and /CLi through the transfer transistors Tri1a and Tri2a. 
Afterwards, the read transfer signal RT is rendered high in level. Thus, the transfer transistors Tri5 and Tri6 of the transfer circuit I are turned on so that the signal lines CLi and /CLi are electrically connected to their corresponding read registers RRi. Accordingly, the data on the signal lines CLi and /CLi are respectively written into the read registers RRi.
This series of operation is called “read transfer”.
<Time t7>
The data transferred from the memory block a to its corresponding read register J are temporarily stored in the read register J according to the read transfer operation. Thereafter, the address YR1 of the outputs produced from the read address accessing circuit C is brought to a high level. Thus, the transfer transistors Trl7 and Trl8 are turned on so that the data stored in the read register RR1 is transferred to the read data buses RD and /RD. The transferred data is transferred to the output circuit M from which it is outputted as data DO1 of the output data DOUT.
<Time t8>
The address YR2 of the outputs produced from the read address accessing circuit C is brought to a high level. Thus, the transfer transistors Tr27 and Tr28 are turned on so that the data stored in the read register RR2 is transferred to the read data buses RD and /RD. The transferred data is transferred to the output circuit M from which it is outputted as data D02 of the output data DOUT.
<Time t9>
The address YRm of the outputs produced from the read address accessing unit C is brought to a high level. Thus, the transfer transistors Trm7 and Trm8 are turned on so that the data stored in the read register RRm is transferred to the read data buses RD and /RD. The transferred data is transferred to the output circuit M from which it is outputted as data DOm of the output data DOUT.
Since the read and write registers are respectively provided one by one (by one set) with respect to the plurality of memory blocks in the serial access memory according to the first embodiment of the present invention as described above, a substantial reduction in chip size can be achieved.
Further, since the write and read registers can be reduced in number as compared with the prior art, it is possible to restrain an increase in the number of peripheral circuits and implement a reduction in power consumption.
FIGS. 3A-3B are a simplified circuit diagram showing a circuit of a principal part of a serial access memory according to a second embodiment of the present invention. A configuration of the second embodiment will be explained below with reference to FIGS. 3A-3B. In FIGS. 3A-3B, the same portions as those shown in FIGS. 1A-1B are identified by the same reference numerals and the description thereof will therefore be omitted.
The second embodiment is similar to the first embodiment in that the serial access memory according to the present embodiment comprises two memory blocks a and b. However, transfer control for controlling transfer circuits Ha and Hb are respectively performed based on two transfer signals CT1a and CT2a, and CT1b and CT2b. The transfer signal CT1a is supplied to the gates of odd-numbered transfer transistors (e.g., Tr 1a and Tr12a) of the transfer circuit, whereas the transfer signal CT2a is supplied to the gates of even-numbered transfer transistors (e.g., Tr21a and Tr22a) of the transfer circuit. Similarly, the transfer signal CT1b is supplied to the gates of odd-numbered transfer transistors (e.g., Tr11b and Tr12b) of the transfer circuit, whereas the transfer signal CT2b is supplied to the gates of even-numbered transfer transistors (e.g., Tr21b and Tr22b) of the transfer circuit.
Read registers RRi and write registers WRi are respectively electrically connected to both ends of odd-numbered signal lines (e.g., CL1 and /CL1) through transfer circuits I and F. On the other hand, the read registers and the write registers are respectively disconnected from both ends of even-numbered signal lines (e.g., CL2 and /CL2) and only the transfer circuits I and F are respectively connected thereto. The transfer circuits I and F connect the even-numbered signal lines (e.g., CL2 and /CL2) to the read registers RRi and the write registers WRi respectively electrically connected to both ends of the odd-numbered signal lines (e.g., CL1 and /CL1), respectively.
Of the transfer circuit F, transfer transistors (e.g., Tr 3 and Tr 4) respectively electrically connected to the odd-numbered signal lines (e.g., CL1 and /CL1) are controlled by a first write transfer signal WT1, and transfer transistors (e.g., Tr 9 and Tr10) respectively electrically connected to the even-numbered signal lines (e.g., CL2 and /CL2) are controlled by a second write transfer signal WT2. Of the transfer circuit 1, transfer transistors (e.g., Trl5 and Trl6) respectively electrically connected to the odd-numbered signal lines (e.g., CL1 and /CL1) are controlled by a first read transfer signal RT1, and transfer transistors (e.g., Tr11 and Tr 12) respectively electrically connected to the even-numbered signal lines (e.g., CL2 and /CL2) are controlled by a second read transfer signal RT2.
FIG. 4 is a timing chart for describing timings provided to operate the serial access memory according to the second embodiment of the present invention. The operating timings for the serial access memory according to the second embodiment will be explained below according to times t1 through t6 with reference to FIG. 4. Incidentally, FIG. 4 shows operating states for explanation regardless of an actual serial access memory in a manner similar to FIG. 2.
<Time t1>
An input circuit L captures data DI11 from input data DIN and transfers it to write data buses WD and /WD. A write address accessing circuit B selectively activates an address signal YW1. Thus, transfer transistors Tr11 and Tr12 of a transfer circuit D are selectively turned on to electrically connect the write register WR1 to the write data buses WD and NVD. Accordingly, the data DI11 is written into the write register WR1.
<Time t2>
The input circuit L brings data DI1k from the input data DIN and transfers it to the write data buses WD and /WD. The write address accessing circuit B selectively activates an address signal YWk. Thus, transfer transistors Trk1 and Trk2 of the transfer circuit D are selectively turned on to electrically connect the write register WRk to the write data buses WD and /WD. Accordingly, the data DI1k is written into the write register WRk.
<Time t3>
After the writing of the data into the write register WRk has been completed, the written data DI11 through DI1k are written into their corresponding memory cells electrically connected to bit line pairs (e.g., BL1a ad /BL1a) lying in odd sequences, of a memory array Ga at a time t3. At first, an X address accessing circuit Aa selects the corresponding word line WL1a (tentatively set as WL1a for explanation herein) and supplies a signal of a high level to the word line WL1a. Thus, memory cell transistors CTri1a of the memory cells connected to the word line WL1a are turned on, thus bringing the memory cells to a selected state.
Since the first write transfer signal WT1 is brought to a high level simultaneously, the transfer transistors Tri3 and Tri4 are turned on. Thus, the data written into the write registers WRi are temporarily transferred onto their corresponding signal lines CLi and /CLi through the transfer transistors Trk3 and Trk4.
After the data have fully been transferred to the signal lines CLi and /CLi, the transfer signal CT1a is rendered high in level. Thus, the transfer transistors Tri1a and Tri2a of the transfer circuit Ha are turned on to electrically connect the signal lines CLi and /CLi to their corresponding bit lines BLia and /BLia. Accordingly, the data on the signal lines CLi and /CLi are temporarily transferred to the bit lines BLia and /BLia. The transferred data are respectively amplified by sense amplifiers SAia and thereafter stored in their corresponding capacitors Ci1a of the memory cells (corresponding to the memory cells whose memory cell transistors CTri1a are kept on) connected to the word line WL1a. 
<Time t4>
The input circuit L takes in data D121 from the input data DIN and transfers it to the write data buses WD and /WD. The write address accessing circuit B selectively activates an address signal YW1. Thus, the transfer transistors Tr 1 and Trl2 of the transfer circuit D are selectively turned on to electrically connect the write register WR1 to the write data buses WD and /WD. Accordingly, the data D121 is written into the write register WR1.
<Time t5>
The input circuit L takes in data D12k from the input data DIN and transfers it to the write data buses WD and /WD. The write address accessing circuit B selectively activates an address signal YWk. Thus, the transfer transistors Trk1 and Trk2 of the transfer circuit D are selectively turned on to electrically connect the write register WRk to the write data buses WD and /WD. Accordingly, the data DI2k is written into the write register WRk.
<Time t6>
After the writing of the data into the write register WRk has been completed, the written data D121 through D12k are written into their corresponding memory cells electrically connected to bit line pairs (e.g., BL2a and /BL2a) lying in even sequences, of the memory array Ga at a time t6.
At first, the X address accessing circuit Aa selects the corresponding word line WL2a (tentatively set as WL2a for explanation herein) and supplies a signal of a high level to the word line WL2a. Thus, memory cell transistors CTri2a of the corresponding memory cells connected to the word line WL2a are turned on, so that the memory cells are brought to a selected state.
Since the second write transfer signal WT2 is brought to a high level simultaneously, the transfer transistors (Tr9 and Tr10) are turned on. Thus, the data written into the write registers WRi are temporarily transferred onto their corresponding signal lines CLi and /CLi through the transfer transistors (e.g., Trl9 and Tr10).
After the data have fully been transferred to the signal lines CLi and /CLi, the transfer signal CT2a is rendered high in level. Thus, the transfer transistors Tri1a and Tri2a of the transfer circuit Ha are turned on to electrically connect the signal lines CLi and /CLi to their corresponding bit lines BLia and /BLia. Accordingly, the data on the signal lines CLi and /CLi are temporarily transferred to the bit lines BLia and /BLia. The transferred data are respectively amplified by the sense amplifiers SAia and thereafter stored in their corresponding capacitors Ci1a of the memory cells (corresponding to the memory cells whose memory cell transistors CTri1a are kept on) connected to the word line WL2a. 
Incidentally, while only the read operation has been described in the second embodiment, a write operation can easily be understood if a reference is made to the write operation of the first embodiment and the read operation of the second embodiment.
Since the read and write registers are respectively configured in half number in the second embodiment as described above as compared with the first embodiment, a reduction in chip size, restraint on an increase in the number of peripheral circuits, and low power consumption can be achieved as compared with the first embodiment.
FIGS. 5A-5C are a simplified circuit diagram showing a circuit of a principal part of a serial access memory according to a third embodiment of the present invention. In FIGS. 5A-5C, the same portions as those shown in FIGS. 1A-1B are identified by the same reference numerals and the description thereof will therefore be omitted. A configuration of the third embodiment will be explained below with reference to FIGS. 5A-5C.
The serial access memory according to the third embodiment is one wherein one read register (one set) is additionally provided to set the read port of the first embodiment to two. Namely, the configuration of the serial access memory according to the third embodiment is one obtained by adding the following configuration to the first embodiment.
Added read registers RRi′ are respectively electrically connected to first ends of signal lines CLi and /CLi through an added transfer circuit 1′ on the connection side of read registers RRi through a transfer circuit 1. The added read registers RRi′ respectively comprise two inverters whose input and output are connected to each other, in a manner similar to the read registers RRi. Further, the added transfer circuit I′ also comprises added transistor pairs Tri5′ and Tri6′ in a manner similar to the transfer circuit 1. The added transfer transistors Tri5′ or Tri6′ have first terminals respectively electrically connected to the added read registers RRi′, second terminals respectively electrically connected to the signal lines CLi and /CLi, and gates respectively commonly supplied with a read transfer signal RT′.
Further, the added read registers RRi′ are also electrically connected to added read data buses RD′ and /RD′ through a transfer circuit K′. The transfer circuit K′ comprises added transfer transistor pairs Tri7′ and Tri8′. First terminals of the added transfer transistors Tri7′ and Tri8′ are respectively electrically connected to the added read registers RRi′, second terminals thereof are respectively electrically connected to the added read data buses RD′ and /RD′, and their gates are respectively commonly supplied with added address signals YRm′. The added address signals YRm′ are generated by an added read address accessing circuit C′. The added read address accessing circuit C′ activates only one added address signal YRm′ in response to an unillustrated address signal. Thus, only data stored in the added read registers RRi′ connected to the added transfer transistor pairs Tri7′ and Tri8′ supplied with the activated added address signal YRm′ are read into the added read data buses RD′ and /RD′.
An added output circuit M′ is electrically connected to the added read data buses RD′ and /RD′. The added output circuit M′ outputs the data outputted to the added read data buses RD′ and /RD′ to the outside as added output data DOUT′.
The operation of the serial access memory according to the third embodiment will next be described with reference to FIG. 6. Since the serial access memory according to the third embodiment is similar in write operation to the first embodiment, the description thereof will be omitted and only a read operation thereof will be explained.
<Time t1>
An X address accessing circuit Aa selects the corresponding word line WL1a (which is tentatively set as WL1a for explanation herein) and supplies a high level signal to the word line WL1a. Thus, memory cell transistors CTri1a of memory cells connected to the word line WL1a are turned on to transfer data stored in capacitors Ci1a of the memory cells to their corresponding bit lines pairs BLia and /BLia. Sense amplifiers SAia respectively amplify the data on the bit line pairs BLia and /BLia.
<Time t2>
Since a transfer signal CTa is rendered high in level, transfer transistors Tri1a and Tri2a of a transfer circuit Ha are turned on so that the signal lines CLi and /CLi are electrically connected to their corresponding bit line pairs BLia and /BLia. Thus, the data on the bit line pairs BLia and /BLia, which have been amplified by the sense amplifiers SAia, are temporarily transferred onto the signal lines CLi and /CLi through the transfer transistors Tri1a and Tri2a. 
Afterwards, a read transfer signal RT is rendered high in level. Thus, transfer transistors Tri5 and Tri6 of the transfer circuit I are turned on to electrically connect the signal lines CLi and /CLi to their corresponding read registers RRi. Accordingly, the data on the signal lines CLi and /CLi are respectively written into the read registers RRi. This is called a so-called read transfer operation.
<Time t3>
An X address accessing unit Ab selects the corresponding word line WL1b (which is tentatively set as WL1b for explanation herein) and supplies a high level signal to the word line WL1b. Thus, memory cell transistors CTri1b of memory cells connected to the word line WL1b are turned on so that data stored in capacitors Ci1b of the memory cells are transferred to their corresponding bit lines pairs BLib and /BLib. Sense amplifiers SAib respectively amplify the data on the bit line pairs BLib and /BLib.
<Time t4>
Since a transfer signal CTb is rendered high in level, transfer transistors Tri1b and Tri2b of a transfer circuit Hb are turned on to electrically connect the signal lines CLi and /CLi to their corresponding bit lines BLib and /BLib. Thus, the data on the bit line pairs BLib and /BLib, which have been amplified by the sense amplifiers SAib, are temporarily transferred onto the signal lines CLi and /CLi through the transfer transistors Tri1b and Tri2b. 
Afterwards, the added read transfer signal RT′ is rendered high in level. Thus, the added transfer transistors Tri5′ and Tri6′ of the added transfer circuit I′ are turned on so that the signal lines CLi and /CLi are electrically connected to their corresponding added read registers RRi′. Accordingly, the data on the signal lines CLi and /CLi are respectively written into the added read registers RRi′. Namely, this is called an added read transfer operation.
<Time t5>
Data transferred from a memory cell or memory block a to its corresponding read register J are temporarily stored in the read register J according to the read transfer operation. Data transferred from a memory cell or memory block b to its corresponding added read register J′ are temporarily stored in the added read register J′. Thereafter, an address YR1 of outputs produced from a read address accessing circuit C is brought to a high level, and an address YR1′ of outputs produced from the added read address accessing circuit C′ is rendered high in level. Thus, transfer transistors Tr 7 and Tr 8 are turned on so that the data stored in the read register RR1 is transferred to the corresponding read data buses RD and /RD. Further, added transfer transistors Tr 7′ and Tr 8′ are turned on so that the data stored in the added read register RR1′ is transferred to the corresponding added read data buses RD′ and /RD′. The transferred data are transferred to their corresponding output circuits M and added output circuits M′ from which they are outputted as data DO1 and added data DO1′ of output data DOUT and added output data DOUT′.
<Time t6>
An address YR2 of the outputs produced from the read address accessing circuit C is brought to a high level, and an address YR2′ of the outputs produced from the added read address accessing circuit C′ is rendered high in level. Thus, the transfer transistors Tr 7 and Tr 8 are turned on so that the data stored in the read register RR2 is transferred to the read data buses RD and /RD. Further, the added transfer transistors Tr 7′ and Tr 8′ are turned on so that the data stored in the added read register RR2′ is transferred to the corresponding added read data buses RD′ and /RD′. The transferred data are transferred to their corresponding output circuits M and added output circuits M′ from which they are outputted as data D02 and added data D02′ of the output data DOUT and added output data DOUT′.
<Time t7>
An address YRm of the outputs produced from the read address accessing circuit C is brought to a high level, and an address YRm′ of the outputs produced from the read address accessing circuit C′ is rendered high in level. Thus, the transfer transistors Trl7 and Trl8 are turned on so that the data stored in the read register RRm is transferred to the read data buses RD and /RD. Further, the added transfer transistors Trl7′ and Trl8′ are turned on so that the data stored in the added read register RRm′ is transferred to the corresponding added read data buses RD′ and /RD′. The transferred data are transferred to their corresponding output circuit M and added output circuit M′ from which they are outputted as data DOm and added data DOm′ of the output data DOUT and added output data DOUT′.
The serial access memory according to the third embodiment is disadvantageous over the first embodiment in both chip size and current consumption because the added read registers are additionally provided as compared with the first embodiment. However, the serial access memory has the advantage of being capable of simultaneously obtaining outputs from the two output circuits as is understood from FIG. 6.
FIGS. 7A-7B are a simplified circuit diagram showing a circuit of a principal part of a serial access memory according to a fourth embodiment of the present invention. In FIGS. 7A-7B, the same portions as those shown in FIGS. 1A-1B are identified by the same reference numerals and their description will be omitted. A configuration of the fourth embodiment will be explained below with reference to FIGS. 7A-7B.
The serial access memory according to the fourth embodiment is equivalent to one wherein the transfer circuits F and I employed in the first embodiment are respectively made up of only one transistor. Namely, in the fourth embodiment, the transfer circuits F and I respectively connect a write register E and a read register J to only either of signal lines CLi and /CLi.
Only points different from the first embodiment will be explained in the fourth embodiment. The transfer circuits F and I comprise respective one transistors Tri4 and Tri5 respectively. Transfer transistors Tri4 have first terminals electrically connected to their corresponding write registers WRi, second terminals electrically connected to their corresponding signal lines CLi (which may be /CLi although CLi have been used in the present embodiment), and gates each supplied with a write transfer signal WT. Further, the transfer transistors Tri5 have first terminals electrically connected to their corresponding read registers RRi, second terminals electrically connected to their corresponding signal lines CLi (which may be /CLi although the CLi have been used in the present embodiment), and gates each supplied with a read transfer signal RT.
The serial access memory according to the fourth embodiment has the possibility that it will become advantageous over the first embodiment in chip size because the number of transistors is low as compared with the first embodiment. However, no data is supplied to the signal lines disconnected from the transfer circuits F and 1. Accordingly, the serial access memory has the potential for an increase in the load on each sense amplifier and the need for much time.
FIGS. 8A-8B are a simplified circuit diagram showing a circuit of a principal part of a serial access memory according to a fifth embodiment of the present invention. In FIGS. 8A-8B, the same portions as those shown in FIGS. 7A-7B are identified by like reference numerals and their description will be omitted. A configuration of the fifth embodiment will be explained below with reference to FIGS. 8A-8B.
The serial access memory according to the fifth embodiment is equivalent to one wherein the transfer circuits Ha and Hb employed in the fourth embodiment are respectively made up of only one transistor, and the number of signal lines is set to one alone without being set in pairs. Namely, in the fifth embodiment, the transfer circuits Ha and Hb respectively connect bit line pairs BLia or /BLia, or BLib or /BLib to signal lines CLi.
Only points different from the fourth embodiment will be explained in the fifth embodiment. The transfer circuits Ha and Hb comprise respective one transistors Tri2a and Tri2b respectively. The transfer transistors Tri2a have first terminals electrically connected to their corresponding bit line pairs BLia (which may be /BLia although BLia have been used in the present embodiment), second terminals electrically connected to their corresponding signal lines CLi, and gates each supplied with a write transfer signal WT. Further, the transfer transistors Tri2b have first terminals electrically connected to their corresponding bit line pairs BLib (which may be /BLib although BLib have been used in the present embodiment), second terminals electrically connected to their corresponding signal lines CLi, and gates each supplied with a read transfer signal RT.
The serial access memory according to the fifth embodiment is advantageous over the fourth embodiment in chip size because the number of transistors and the number of signal lines are low as compared with the fourth embodiment. However, no data is supplied to the bit lines disconnected from the transfer circuits Ha and Hb. Accordingly, the serial access memory has the potential for an increase in the load on each sense amplifier and the need for much time.
FIGS. 9A-9B are a simplified circuit diagram showing a circuit of a principal part of a serial access memory according to a sixth embodiment of the present invention. In FIGS. 9A-9B, the same portions as those shown in FIGS. 3A-3B are identified by the same reference numerals and their description will be omitted. A configuration of the sixth embodiment will be explained below with reference to FIGS. 9A-9B.
The serial access memory according to the sixth embodiment has a configuration wherein one pair of the signal line pairs CLi and /CLi is provided for the two pairs of the bit line pairs BLia and /BLia, or the two pairs of the bit line pairs BLib and /BLib in the second embodiment. Therefore, transfer circuits F and I are simply provided in association with the signal line pairs CLi and /CLi, and one control signal is used therefor in a manner similar to the first embodiment. Transfer circuits Ha and Hb are respectively connected to one pair of the signal line pairs CLi and /CLi common to the two pairs of the bit line pairs BLia and /BLia or BLib and /BLib.
Only points different from the second embodiment will be explained in the sixth embodiment.
The bit line pairs BLia and /BLIa or BLib and /BLib set in column units are electrically connected to their corresponding pairs of signal lines CLk and /CLk parallel to the bit line pairs BLia, /BLia, BLib or /BLib and common to memory blocks a and b through the transfer circuits Ha and Hb. Here, the signal line pairs CLk and /CLk are provided commonly to the two pairs (e.g., BL1a and /BL1a and BL2a and /BL2a, or BL1b and /BLib and BL2b and /BL2b) of the bit line pairs.
The transfer circuits Ha or Hb comprises transfer transistor pairs Tri1a and Tri2a or Tri1b and Tri2b. The odd-numbered transfer transistor (e.g., Tri11a, Trl2a, Tr11b or Tri12b) has a first terminal electrically connected to Its corresponding bit line (e.g., BL1a, [bL1a/]/BL1a, BL1b or /BL1b), a second terminal electrically connected to its corresponding signal line (e.g., CL1, /CL1) and a gate commonly supplied with a fist transfer signal CT1a or CT1b. On the other hand, the even-numbered transfer transistor (e.g., Tr21a, Tr22a, Tr21b or Tr22b) has a first terminal electrically connected to its corresponding bit line (e.g., BL2a, /BL2a, /BL2b), a second terminal electrically connected to its corresponding signal line (e.g., CL1, /CL1) common to the odd-numbered one, and a gate commonly supplied with a second transfer signal CT2a or CT2b. 
Read and write registers RRk and WRk are electrically connected to their corresponding both ends of the signal lines CLk and /CLk through the transfer circuits I and F. The transfer circuits F and I respectively comprise transistor pairs Trk3 and Trk4 or Trk5 and Trk6. The transfer transistor Trk3 or Trk4 has a first terminal electrically connected to its corresponding write register WRk, a second terminal electrically connected to its corresponding signal line CLk or /CLk and a gate commonly supplied with a write transfer signal WT. Further, the transfer transistor Trk5 or Trk6 has a first terminal electrically connected to its corresponding read register RRk, a second terminal electrically connected to its corresponding signal line CLk or /CLk and a gate commonly supplied with a read transfer signal RT.
The serial access memory according to the sixth embodiment can be reduced in chip size as compared with the second embodiment because the number of the signal line pairs and the number of the transfer circuits for connecting the signal line pairs and the read and write registers are low as compared with the second embodiment.
FIGS. 10A-10B are a simplified circuit diagram showing a circuit of a principal part of a serial access memory according to a seventh embodiment of the present invention. In FIGS. 10A-10B, the same portions as those shown in FIGS. 9A-9B are identified by the same reference numerals and their description will be omitted. A configuration of the seventh embodiment will be explained below with reference to FIGS. 10A-10B.
The serial access memory according to the seventh embodiment is provided with a dividing circuit N for separating the memory block a and the memory block b employed in the sixth embodiment from each other.
Only points different from the sixth embodiment will be explained in the seventh embodiment.
Signal line pairs common to memory blocks a and b employed in the seventh embodiment are divided into signal line pairs CLk and /CLk for the memory block a and signal line pairs CLk′ and /CLk′ for the memory block b. The dividing circuit N controls connections or non-connections between the divided signal line pairs. The dividing circuit N comprises dividing transistor pairs TrBk and /TrBk. The dividing transistors TrBk respectively have first terminals electrically connected to their corresponding signal line pairs CLk, second terminals electrically connected to their corresponding signal line pairs CLk′ and gates supplied with a division signal BS. On the other hand, the dividing transistors /TrBk respectively have first terminals electrically connected to their corresponding signal lines pairs /CLk, second terminals electrically connected to their corresponding signal lines pairs /CLk′ and gates supplied with the division signal BS. The serial access memory according to the seventh embodiment is disadvantageous over the sixth embodiment in a reduction in chip size because the dividing circuit is additionally provided. However, the serial access memory according to the seventh embodiment has the operational merit of being capable of separating the memory block a and the memory block b by the dividing circuit to thereby execute a read transfer and a write transfer simultaneously.
FIGS. 11A-11B is a simplified circuit diagram showing a circuit of a principal part of a serial access memory according to an eighth embodiment of the present invention. A configuration of the eighth embodiment will be explained below with reference to FIGS. 11A-11B. In FIGS. 11A-11B, the same portions as those shown in FIGS. 1A-1B are identified by the same reference numerals and their description will be omitted.
The serial access memory according to the present embodiment uses registers as read/write registers held in common or shared for write/read without exclusively using the registers as in the case of the read register and the write register. Thus, as is understood from a comparison made between FIGS. 1A-1B and FIGS. 11A-11B, the serial access memory according to the eighth embodiment has a configuration in which the read registers of the serial access memory according to the first embodiment are omitted.
Only points different from the first embodiment will be explained in the eighth embodiment. Only write/read registers WRm electrically connected to their corresponding one ends of signal line pairs CLi and /CLi are used as registers employed in the eighth embodiment. Thus, data buses are configured as input/output data buses WRD and /WRD, and an input/output circuit L′ handles input data DIN and output data DOUT.
In the serial access memory according to the eighth embodiment, a reduction in chip size can be achieved because the read registers (or write registers), transfer circuits related thereto, buses and output circuits (or input circuits) can be omitted as compared with the first embodiment. Since, however, the registers are held in write/read common use in the serial access memory according to the eighth embodiment, the serial access memory has the demerit of being unable to asynchronously simultaneously perform a write operation and a read operation.
According to the invention of the present application as described above in detail, a serial access memory low in current consumption can be provided which is capable of restraining an increase in chip size even if memory capacity increases.
While the present invention has been described with reference to the illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to those skilled in the art on reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.

## Claims

1. A serial access memory comprising:
a first memory array including a plurality of first memory cells, a first sense amplifier and a pair of first bit lines connected to the first memory cells and the first sense amplifier; 
a second memory array including a plurality of second memory cells, a second sense amplifier and a pair of second bit lines connected to the second memory cells and the second sense amplifier; 
a pair of column lines selectively connected to the first bit lines or the second bit lines, the column lines being located substantially parallel with the first and second bit lines; 
a write register connected to the column lines; 
a read register connected to the column lines; 
a control circuit selectively connecting the column lines with the first bit lines or the second bit lines; and 
an input/output circuit selectively connected to the registers.

2. A serial access memory according to claim 1, wherein the input/output circuit includes an input circuit selectively connected to the write register and an output circuit selectively connected to the read register.

3. A serial access memory according to claim 1, further comprising an additional read register connected to the column lines and an additional output circuit connected to the additional read register.

4. A serial access memory according to claim 1, wherein the control circuit comprises:
a first transfer circuit connected between the column lines and the first bit lines, the first transfer circuit connecting the column lines with the first bit lines in response to a first control signal; and 
a second transfer circuit connected between the column lines and the second bit lines, the second transfer circuit connecting the column lines with the second bit lines in response to a second control signal.

5. A serial access memory according to claim 4, further comprising:
a third transfer circuit connected between the column lines and the read register, the third transfer circuit connecting the column lines with the read registers in response to a third control signal; and 
a fourth transfer circuit connected between the read register and the input/output circuit, the fourth transfer circuit connecting the read register with the input/output circuit in response to a fourth control signal.

6. A serial access memory according to claim 5, further comprising:
a fifth transfer circuit connected between the column lines and the write register, the fifth transfer circuit connecting the column lines with the write register in response to a fifth control signal; and 
a sixth transfer circuit connected between the write register and the input/output circuit, the sixth transfer circuit connecting the write register with the input/output circuit in response to a sixth control signal.

7. A serial access memory according to claim 1, wherein the read register is selectively connected to two pairs of column lines, and the write register is selectively connected to the two pairs of column lines.

8. A serial access memory comprising:
a first memory array including a plurality of first memory cells, a first sense amplifier and a pair of first bit lines connected to the first memory cells and the first sense amplifier; 
a second memory array including a plurality of second memory cells, a second sense amplifier and a pair of second bit lines connected to the second memory cells and the second sense amplifier; 
a column line selectively connected to one of the first bit lines or one of the second bit lines, the column line being located substantially parallel with the first and second bit lines; 
a register connected to the column line; 
a control circuit selectively connecting the column line with the one of the first bit lines or the one of the second bit lines; and 
an input/output circuit selectively connected to the register.

9. A serial access memory according to claim 8, wherein the input/output circuit includes an input circuit and an output circuit, and the register includes a read register and a write register, and wherein the input circuit is selectively connected to the write register and the output circuit is selectively connected to the read register.

10. A serial access memory according to claim 8, further comprising an additional read register connected to the column line and an additional output circuit connected to the additional read register.

11. A serial access memory according to claim 8, wherein the control circuit comprises:
a first transfer circuit connected between the column line and the one of the first bit lines, the first transfer circuit connecting the column line with the one of the first bit lines in response to a first control signal; and 
a second transfer circuit connected between the column line and the one of the second bit lines, the second transfer circuit connecting the column line with the one of the second bit lines in response to a second control signal.

12. A serial access memory according to claim 11, further comprising a third transfer circuit connected between the column line and the register, the third transfer circuit connecting the column line with the register in response to a third control signal.

13. A serial access memory according to claim 8, wherein the register is selectively connected to two column lines.

14. A serial access memory comprising:
a first memory array including a plurality of first memory cells, a plurality of first sense amplifiers and a plurality of pairs of first bit lines each of which is connected to the first memory cells and the first sense amplifiers; 
a second memory array including a plurality of second memory cells, a plurality of second sense amplifiers and a plurality of pairs of second bit lines each of which is connected to the second memory cells and the second sense amplifiers; 
a plurality of column lines selectively connected to one of the first bit lines or one of the second bit lines, the column lines being located substantially parallel with the first and second bit lines; 
a plurality of registers each of which is connected to one of the column lines; 
a control circuit selectively connecting one of the column lines with one of the first bit lines or the second bit lines; and 
a plurality of input/output circuits each of which is selectively connected to one of the registers.

15. A serial access memory according to claim 14, wherein the input/output circuits include a plurality of input circuits and a plurality of output circuits, and the registers include a plurality of read registers and a plurality of write registers, and wherein the input circuits are selectively connected to the write registers and the output circuits are selectively connected to the read registers.

16. A serial access memory according to claim 15, further comprising a plurality of additional read registers connected to the column lines and a plurality of additional output circuits connected to the additional read registers.

17. A serial access memory according to claim 14, wherein the control circuit comprises:
a first transfer circuit connected between the column lines and the first bit lines, the first transfer circuit connecting the column lines with the first bit lines in response to a first control signal; and 
a second transfer circuit connected between the column lines and the second bit lines, the second transfer circuit connecting the column lines with the second bit lines in response to a second control signal.

18. A serial access memory according to claim 17, further comprising a third transfer circuit connected between the column lines and the register, the third transfer circuit connecting the column lines with the registers in response to a third control signal.

19. A serial access memory according to claim 14, wherein one of the registers is selectively connected to two of the column lines.