Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Utilizing three or more electrode solid-state device
Reexamination Certificate
1999-08-09
2001-03-06
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Utilizing three or more electrode solid-state device
C327S426000, C326S036000
Reexamination Certificate
active
06198336
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a threshold element used in a logical operation circuit. More specifically, the present invention relates to a threshold element using a MIS (metal insulator semiconductor) transistor.
2. Description of the Related Art
As conventional threshold elements, threshold elements based on output-wired CMOS (complementary metal-oxide semiconductor) inverters have been known.
FIG. 8
shows a configuration of a conventional threshold element using an output-wired CMOS inverter. In this element, each of inputs X
1
, X
2
, . . . X
n
has a corresponding inverter
1
,
2
, . . . n. Outputs from these inverters are all wired together, creating an output voltage Vout. The output voltage Vout is input to a comparing inverter
10
. A threshold value of the comparing inverter (judging inverter)
10
is set appropriately so that a majority result can be converted into binary data properly. In this threshold element, the output voltage Vout reflecting a sum of the outputs from the inverters
1
through n corresponding to the inputs X
1
through X
n
is compared with a threshold value by the comparing inverter. If the output voltage Vout is larger than the threshold value, “1” is output as a final result y. Otherwise, “0” is output. The threshold element can be used for various kinds of logical operations, by applying an appropriate weight to each of the inputs X
1
through X
n
and setting a suitable threshold value to the comparing inverter
10
.
In the above-described conventional technique, at least 2 transistors are required for each input, which leads to a problem that a large area on a substrate is occupied by the threshold circuit. Furthermore, weighting each inverter for each input as well as designing and setting the proper threshold value for the judging inverter are complicated.
An object of the present invention is therefore to provide a threshold element enabling a logical operation with fewer transistors, easy element weighting, and easy design and setting of the threshold value.
SUMMARY OF THE INVENTION
In order to achieve the above object, a threshold element of the present invention comprises MIS (Metal Insulator Semiconductor) transistors connected in parallel each passing a drain current in accordance with &ohgr;i obtained by an expression Y=Sign (&Sgr;&ohgr;iXi−1) transformed from a logical expression Y=F(Xi) upon excitation thereof and each having a terminal connected to a gate electrode thereof for transmitting a corresponding input signal Xi controlling the excitation thereof, and a comparing inverter for comparing an output voltage in accordance with a sum of the drain current from each of the transistors with a threshold value and for outputting a comparison result.
In the threshold element of the present invention, the MIS transistors may determine their &bgr; values by the width and length of their gate electrodes. It is more preferable for the threshold element that each unit of the MIS transistor further comprises a second MIS transistor as means for transmitting the input signal Xi so that the transistor unit can be switched on and off by the input signal applied to a gate electrode of the second transistor, while an effective &bgr; value of the transistor unit can be adjusted by a voltage applied to a gate electrode of the first transistor.
According to the threshold element of the present invention, by setting each of the transistors connected in parallel in a state such that the drain current corresponding to &ohgr;i flows therethrough upon excitation thereof, the threshold value of the comparing inverter can always be set to a predetermined value, and design and setting of the threshold element becomes far easier than those of a conventional threshold element. Furthermore, according to the threshold element of the present invention, only one transistor is necessary in principle for each input. Therefore, the threshold element can be formed with fewer transistors. Moreover, if the &bgr; value for passing the drain current corresponding to &ohgr;i can be changed by the voltage applied to the gate electrode of each of the transistors, the &ohgr;i values can be changed upon necessity after designing and forming the threshold element, by changing the voltage applied to the gate electrode of each of the transistors. Therefore, a logical operation circuit with fewer threshold circuits can be formed.
For example, if a logical expression Y is a logical sum or logical product of n inputs Xi, a conventional threshold element needs 2n transistors except for a comparing inverter, whereas the present invention needs (n+1) transistors which are approximately half of the transistors for the conventional element. Furthermore, in the case where the threshold element is incorporated into an integrated circuit, all inputs are applied to the transistors of the same channel type connected in parallel. Therefore, extremely easy design and layout can be realized. More specifically, for example, if the logical expression Y is a 3-input logical expression such as X
1
(X
2
+X
3
), X
1
X
2
+X
2
X
3
+X
3
X
1
, and X
1
X
2
X
3
, the conventional threshold element needs 6 transistors in addition to a comparing inverter, while the threshold element of the present invention needs only 4 transistors. Furthermore, NOT logic can be dealt with by inserting an inverter.
REFERENCES:
patent: 3715603 (1973-02-01), Lerch
patent: 4896059 (1990-01-01), Goodwin-Johansson
Cunningham Terry D.
Monolith Company, Ltd.
Morrison & Foerster / LLP
Tra Quan
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