Static information storage and retrieval – Read/write circuit – Having particular data buffer or latch
Reexamination Certificate
2000-02-04
2001-10-09
Nguyen, Viet Q. (Department: 2818)
Static information storage and retrieval
Read/write circuit
Having particular data buffer or latch
C365S189011, C365S203000, C365S191000
Reexamination Certificate
active
06301160
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a bus driving circuit for driving a bus line provided in a large scale integrated circuit. More specifically, the invention relates to a bus driving circuit used for transferring output data from a pre-charge type circuit via a bus line.
2. Description of the Prior Art
In recent years, large scale integrated circuits (LSIs) are large-scaled and accelerated at a request for the advance of the fine patterning technology and the improvement of the system performance.
As microprocessors, LSIs having a plurality of circuit blocks therein have a bus line for connecting these circuit blocks.
For example, as shown in
FIG. 3
, a large memory unit
30
built in a microprocessor is separated into a plurality of memory blocks
30
1
,
30
2
,
30
3
and
30
4
by addresses. The data output terminals of these memory blocks are connected to a bus line
10
via a read circuit
32
and a bus driving circuit
40
. Such a bus line
10
is driven by the bus driving circuit
40
of an activated one of the memory blocks to transfer data to the next stage circuit.
FIG. 4
shows a conventional bus driving circuit. This bus driving circuit
40
A comprises: a tristate buffer
44
comprising a P-channel MOSFET
44
a
and an N-channel MOSFET
44
b
; and a gate control circuit
42
for controlling the gate of each of the MOSFETs of the tristate buffer
44
on the basis of an enable signal and input data.
The gate control circuit
42
comprises an AND gate
42
a
, an inverter
42
b
and an OR gate
42
c
. The AND gate
42
a
performs an AND operation on the basis of the enable signal and the input data to transmit the operated results to the gate of the N-channel MOSFET
44
b
. The OR gate
42
c
performs an OR operation on the basis of the input data and a signal produced by inverting the enable signal by the inverter
42
b
, to transmit the operated results to the gate of the P-channel MOSFET
44
a
. Furthermore, the input data are produced in synchronism with a clock signal. The output of the tristate buffer
44
is connected to the bus line
10
.
The operation of the bus driving circuit
40
A is as follows. When the enable signal is inactive, the output of the tristate buffer
44
has high impedance so as not to drive the bus line
10
. At this time, if the bus driving circuit
40
A is connected to one memory block of the memory unit
30
shown in
FIG. 3
, other memory blocks are activated, and other bus driving circuits connected to the activated memory blocks drive the bus line
10
to perform data transfer.
On the other hand, if the enable signal inputted to the bus driving circuit
40
A is activated, the bus line
10
is driven in accordance with the input data to perform data transfer as shown in FIG.
5
. Furthermore, as shown in
FIG. 4
, an inverter
50
and a latch circuit
60
controlled by a clock signal CK are provided on the next stage circuit side, to which data are transferred. The potential of the bus line
10
holds data until the next memory access is started (until the clock signal CK is raised next time) (see
FIG. 5
)
FIG. 6
shows another example of a conventional bus driving circuit. In a bus driving circuit
40
B shown in
FIG. 6
, the gate control circuit
42
of the bus driving circuit
40
A shown in
FIG. 4
is replaced with a gate control circuit
43
. The gate control circuit
43
comprises an AND gate
43
a
. The AND gate
43
a
performs an AND operation on the basis of input data and an enable signal to transmit the operated results to the gate of an N-channel MOSFET
44
b
of a tristate buffer
44
. Furthermore, to the gate of a P-channel MOSFET
44
a
of the tristate buffer
44
, an inverted signal /PC of a pre-charge signal PC synchronized with a clock signal is inputted.
The conventional bus driving circuit
40
B shown in
FIG. 6
is designed to receive, as data input, the output of a pre-charge type circuit, i.e., a circuit wherein its output is previously set at a low potential and wherein the data transition of the output occurs only when a high potential is outputted. Furthermore, a read circuit
32
for reading data from the memory unit
30
shown in
FIG. 3
is a pre-charge type circuit.
Referring to
FIG. 7
, the operation of the bus driving circuit
40
B, which is shown in FIG.
6
and which is applied to the memory unit
30
, will be described below.
The bus driving circuit
40
B turns the P-channel MOSFET
44
a
ON, in response to the pre-charge signal PC during a memory access, to previously set the bus line
10
at the high potential. Thereafter, although the MOSFET
44
a
is turned OFF, the bus line is held to be the high potential by a latch circuit
70
. Furthermore, the latch circuit
70
is provided on the side of a circuit, to which data are transferred. In such a state, if the enable signal is activated and if high potential data are outputted from the read circuit
32
of the memory unit
30
, the N-channel MOSFET
44
b
is turned ON, so that the bus line
10
is driven at a low potential to perform data transfer (see FIG.
7
). The potential of the bus line
10
is held by the latch circuit
70
even after the memory access ends to set the output of the read circuit
32
at a low potential again until the next memory access is started to pre-charge the bus line
10
by the pre-charge signal /PC (see
FIG. 7
)
As described above, the potential of the bus line
10
connected to the conventional bus driving circuit
40
B shown in
FIG. 6
is held by the latch circuit
70
until the bus line
10
is pre-charged by the pre-charge signal /PC even after the memory access ends to set the output of the read circuit
32
at the low potential again. Therefore, since it is not required to provide the latch circuit
60
for operating in response to the clock signal, which is provided at the next stage of the bus line
10
as shown in
FIG. 4
, the number of gate stages can be smaller than that of the bus driving circuit
40
A shown in
FIG. 4
, and the data transfer can be rapidly carried out.
However, the bus driving circuit shown in
FIG. 6
is weak in noises since the bus line
10
remains being held at the high potential by the latch circuit
70
having a weak driving force when the output of the read circuit
32
has a low potential. In particular, the bus lines
10
are arranged in parallel at a long distance, and the data transitions occur simultaneously, so that there is much noise due to the coupling capacity with the next line.
Therefore, if the next bus line is driven at the low potential, there is some possibility that the potential of the bus line to be held at the high potential changes to the low potential under the influence of the coupling capacity to cause malfunction.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a bus driving circuit capable of inhibiting the influence of the coupling noises between bus lines and of rapidly transferring data.
In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, a bus driving circuit comprises: bus pre-charge means for pre-charging a bus line on the basis of a pre-charge signal produced in synchronism with a clock signal; a tristate buffer for driving the bus line on the basis of a gate control signal; and a gate control circuit for transmitting the gate control signal to the tristate buffer so as not to drive the bus line when an enable signal is in an inactive state, and for transmitting the gate control signal to the tristate buffer so as to drive the but line on the basis of the potential of the bus line and data inputted from a pre-charge type circuit when the enable signal is in an active state.
The gate control circuit may output first and second gate control signals, and the tristate buffer may comprise: a first MOSFET of a first conductive type, which has a source connected to a first power supply, a gate for receiving the first gate control signal, and a drai
Hogan & Hartson L.L.P.
Kabushiki Kaisha Toshiba
Nguyen Viet Q.
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