Memory device

A memory device capable of storing a time element. The memory device includes: i) a threshold element outputting a voltage output when a gate voltage reaches a threshold voltage; ii) two inputs capacitive coupling connected to a gate of the threshold element; iii) the first RC circuit connected to the first input of the two inputs capacitive coupling; iv) the first RC circuit charging capacitance by the constant number in the predetermined time through the predetermined reference voltage inputs; v) the charging voltage of the capacitance inputted into the two inputs capacitive coupling, and vi) an output of the threshold element connected to a memory element whose parameter is time.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a memory device. 
2. Description of the Related Art 
Conventionally, a memory device stores digital information as a voltage 
level. However, more recent memory devices have been required to manage 
multi-information because there is an argument that digital computers are 
limited in their processing ability. Inventors have suggested a way of 
mapping a voltage signal into time space by using an exponential function. 
This process enables multiplication and division calculations in the 
voltage space to be performed as addition and subtraction calculations in 
the time space. 
In order to realize such an idea as a circuit, it is necessary to store 
times elements. However, such a memory means heretofore did not exist. 
SUMMARY OF THE INVENTION 
The present invention solves the above-identified problems with 
conventional memory devices and provides a memory device that is capable 
of storing time elements. 
A memory device of the present invention sets an off-set corresponding to 
the time constant of an RC circuit by using an input voltage, drives a 
threshold element using charging voltage from a capacitance in the RC 
circuit and provides an output of the threshold elements to a memory 
element whose parameter is time.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS OF THE 
INVENTION 
Hereinafter, an embodiment illustrating the principles of the present 
invention is described below with reference to the attached drawings. 
FIG. 1 shows a memory device that has a threshold element Th.sub.1 which 
outputs an output voltage when a gate voltage reaches a threshold voltage. 
Threshold element Th.sub.1 has a gate connected to two inputs of a 
capacitive coupling circuit C.sub.p. The output of circuit C.sub.p is 
connected to the gate of Th.sub.1, and one input (it is shown by the first 
input of C.sub.p) is connected to an RC circuit (shown by RC.sub.1). 
Th.sub.1, C.sub.p and RC.sub.1 define a timer T.sub.1. 
A reference voltage RP is inputted to a resistor R.sub.1 in RC.sub.1. 
Capacitance C.sub.1 has one terminal connected to the first input of 
C.sub.p and the other terminal is connected to ground. The other input of 
C.sub.p (it is shown by the second input) is connected to an input voltage 
X through a switch means Tr.sub.1. 
If a capacitance of C.sub.p is C.sub.2 and C.sub.3, and the output voltage 
is V.sub.1, then we can obtain the formula below. 
EQU V.sub.1 =[C.sub.3 X+C.sub.2 {1-exp(-t/(R.sub.1 C.sub.1)) }]/(C.sub.2 
+C.sub.3) 
According to this formula, Th.sub.1 generates an output voltage V.sub.m (a 
source voltage) when V.sub.1 reaches the threshold voltage Vt.sub.1 of 
Th.sub.1. RP reaches V.sub.m in steps, RC starts to charge, and V.sub.1 is 
equal to Vt.sub.1 in a time tx corresponding to X. 
As shown by a following formula, 
EQU Vt.sub.1 =[C.sub.3 X+C.sub.2 {1-exp(-tx/(R.sub.1 C.sub.1))}]/(C.sub.2 
+C.sub.3), 
at the same time, time tx corresponding to X is obtained. 
If it is possible to keep the time tx in any way, it is the same as keeping 
Vt.sub.1. 
In order to keep tx, reference voltage RP is connected to the second RC 
circuit (it is shown by RC.sub.2) through a switch means Tr.sub.2. 
RC.sub.2 has a resistance R.sub.2 connected to RP, one terminal of a 
capacitance C.sub.4 is connected to a single terminal of R.sub.2, and the 
other terminal of C.sub.4 is through a switch means Tr.sub.3. Tr.sub.3 
also connects the output of Th.sub.1 to ground, and charging of C.sub.4 is 
stopped after opening Tr.sub.3 at the time of tx. RC.sub.1 and RC.sub.2 
are charged by RP at the same time so that a charging voltage of C.sub.4 
has a value corresponding to tx, because charging of RC.sub.2 ends at the 
time of tx. 
If the charging voltage is V.sub.2, then 
EQU V.sub.2 =V.sub.m {1-exp{tx/(R.sub.2 C.sub.4)}. 
That is, the value of V.sub.2 can be used to read the value of X. Here, the 
time constant of the RC circuit is comparatively accurately set, so the 
accuracy of tx is very high. 
It is possible to convert X into tx' corresponding to V.sub.2, if V.sub.2 
is connected to the second input of CP through a switch means Tr.sub.4, 
Tr.sub.1 is shut and Tr.sub.4 is closed. 
In this situation, the voltage to which C.sub.4 is charged corresponds to 
tx', which is 
EQU Vt.sub.1 =[C.sub.3 V.sub.2 +C.sub.2 {1-exp(-tx'/(R.sub.1 C.sub.1 }]. 
Switch means Tr1 and Tr2 are controlled by signal C1, and a switch means 
Tr4 is controlled by control signal C2. 
FIG. 2 shows another embodiment of the present invention. In this 
embodiment, an EPROM (shown by M) is used as a memory element instead of 
RC.sub.2. Generally, the EPROM operates writing in a simple portion with 
the length of the charging pulse. Therefore, it is possible to detect tx 
by reading the voltage level. 
As mentioned above, the present invention provides a memory device that can 
store a time element because a memory device relating to the present 
invention sets an off-set corresponding to the time constant of an RC 
circuit by using an input voltage, drives a threshold element by using a 
charging voltage of a capacitance in the RC circuit and inputs an output 
of the threshold elements into the memory elements whose parameter is 
time.