25-08-2017, 09:32 PM
Memristor – The Fourth Fundamental Element of Electronics
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Introduction
Generally when most people think about electronics, they may initially think of products such as cell phones, radios, laptop computers, etc. others, having some engineering background, may think of resistors, capacitors, etc. which are the basic components necessary for electronics to function. Such basic components are fairly limited in number and each having their own characteristic function. Engineer’s basically knew about R,L,C as basic and fundamental elements of electronics, But, Loen Chua found a new element Memristor, and published his paper in 1971.
A Memristor is a passive two-terminal electronic component for which the resistance (dV/dI) depends in some way on the amount of charge that has flowed through the circuit. When current flows in one direction through the device, the resistance increases; and when current flows in the opposite direction, the resistance decreases, although it must remain positive. When the current is stopped, the component retains the last resistance that it had, and when the flow of charge starts again, the resistance of the circuit will be what it was when it was last active. More generally, a memristor is a two-terminal component in which the resistance depends on the integral of the input applied to the terminals (rather than on the instantaneous value of the input as in a varistor). Since the element "remembers" the amount of current that has passed through it in the past, it was tagged by Chua with the name "memristor." Another way of describing a memristor is that it is any passive two-terminal circuit elements that maintains a functional relationship between the time integral of current (called charge) and the time integral of voltage (often called flux, as it is related to magnetic flux). The slope of this function is called the memristance M and is similar to variable resistance. Batteries can be considered to have memristance, but they are not passive devices. The definition of memristor is based solely on the fundamental circuit variables of current and voltage and their time integrals, just like the resistor, capacitor and inductor.
Resistor
A resistor is a two-terminal electronic component that produces a voltage across its terminals that is proportional to the electric current through it in accordance with Ohm's law which states” Voltage (V) across a resistor is proportional to the current (I) through it where the constant of proportionality is the resistance ®”.
V = IR
Resistors are elements of electrical networks and electronic circuits and are ubiquitous in most electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel/chrome).
Capacitor
A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric. When a voltage potential difference exists between the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force between the plates. The effect is greatest between wide, flat, parallel, narrowly separated conductors.
An ideal capacitor is characterized by a single constant value, capacitance, which is measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them. In practice, the dielectric between the plates passes a small amount of leakage current. The conductors and leads introduce an equivalent series resistance and the dielectric has an electric field strength limit resulting in a breakdown voltage.
Need for Memristors
Memristance (Memory + Resistance) is a property of an Electrical Component that describes the variation in Resistance of a component with the flow of charge. Any two-terminal electrical component that exhibits memristance is known as a Memristor. Memristance is becoming more relevant and necessary as we approach smaller circuits, and at some point when we scale into nano electronics, we would have to take memristance into account in our circuit models to simulate and design electronic circuits properly. An ideal memristor is a passive two-terminal electronic device that is built to express only the property of memristance (just as a resistor expresses resistance and an inductor expresses inductance). However, in practice it may be difficult to build a 'pure memristor,' since a real device may also have a small amount of some other property, such as capacitance (just as any real inductor also has resistance).
Memristors – History and Evolution
Memristor postulated in a seminal 1971 paper in the IEEE Transactions on Circuit Theory by an Electrical Engineer Professor Leon Chua at the University of California, Berkeley. The hold-up over the last 37 years, according to professor Chua, has been a misconception that has pervaded electronic circuit theory. That misconception is that the fundamental relationship in passive circuitry is between voltage and charge.
Anyone familiar with electronics knows the trinity of fundamental components: the resistor, the capacitor, and the inductor. Professor Chua predicted that there should be a fourth element: a memory resistor, or Memristor. Such a device, he figured, would provide a similar relationship between magnetic flux and charge that a resistor gives between voltage and current. In practice, it will act like a resistor whose value could vary according to the current passing through it and which would remember that value even after the current disappeared. As, Professor Leon Chua pointed out in 1971, for the sake of the logical completeness of circuit theory; a fourth passive element should in fact be added to the list. He named this hypothetical element, linking flux and charge, the ‘Memristor’. But no one knew how to build one.
Evolution
Many researchers observed and reported unusual 'hysteresis' in their current-voltage plots of various devices and circuits based on many different types of materials and structures. They were actually seeing memristance, but apparently not aware of it.
All electronic textbooks have been teaching using the wrong variables - voltage and charge - explaining away inaccuracies as anomalies. What they should have been teaching is the relationship between changes in voltage, or flux, and charge.
Without Professor Chua's circuit equations, making use of this device is not possible. It's such a funky thing. People were using all the wrong circuit equations.
Difference from other elements
The reason that the Memristor is radically different from the other fundamental circuit elements is that, unlike them, it carries a memory of its past. The Memristor changes its impedance depending on the current applied. At any given instant, a Memristor is a resistor, where V=IR. However, the application of I will change R accordingly. Dynamically, the Memristor appears as either an impulse or a charge modulated resistor. When the voltage to the circuit is turned off, the Memristor still remembers how much was applied before and for how long. This effect can't be duplicated by any circuit combination of resistors, capacitors, and inductors.
Working Analogy of Memristor
A Memristor effectively stores information because the level of its electrical resistance changes when current is applied. A typical resistor provides a stable level of resistance. By contrast, a Memristor can have a high level of resistance, which can be interpreted as a computer as a "1" in data terms, and a low level can be interpreted as a "0." Thus, data can be recorded and rewritten by controlling current. In a sense, a Memristor is a variable resistor that, through its resistance, reflects its own history. We can get it (resistance changes) with less energy. It is a large amount of resistance change with a small amount of memory.
It is essentially a device that works under alternating current (a.c.) conditions in which the applied voltage varies sinusoidally with time. As the polarity of this voltage changes, the Memristor can switch reversibly between a less conductive OFF state and a more conductive ON state. Crucially, the value of the current flow through the Memristor (the measure of its resistance) does not in the second half of the cycle retrace the exact path it took in the first. Because of this ‘hysteresis’ effect, the Memristor acts as a nonlinear resistor the resistance of which depends on the history of the voltage across it — its name, a contraction of ‘memory resistor’, reflects just that property. The Memristor is a special case of a more general class of nonlinear dynamical devices called memristive systems.
[attachment=63796]
Introduction
Generally when most people think about electronics, they may initially think of products such as cell phones, radios, laptop computers, etc. others, having some engineering background, may think of resistors, capacitors, etc. which are the basic components necessary for electronics to function. Such basic components are fairly limited in number and each having their own characteristic function. Engineer’s basically knew about R,L,C as basic and fundamental elements of electronics, But, Loen Chua found a new element Memristor, and published his paper in 1971.
A Memristor is a passive two-terminal electronic component for which the resistance (dV/dI) depends in some way on the amount of charge that has flowed through the circuit. When current flows in one direction through the device, the resistance increases; and when current flows in the opposite direction, the resistance decreases, although it must remain positive. When the current is stopped, the component retains the last resistance that it had, and when the flow of charge starts again, the resistance of the circuit will be what it was when it was last active. More generally, a memristor is a two-terminal component in which the resistance depends on the integral of the input applied to the terminals (rather than on the instantaneous value of the input as in a varistor). Since the element "remembers" the amount of current that has passed through it in the past, it was tagged by Chua with the name "memristor." Another way of describing a memristor is that it is any passive two-terminal circuit elements that maintains a functional relationship between the time integral of current (called charge) and the time integral of voltage (often called flux, as it is related to magnetic flux). The slope of this function is called the memristance M and is similar to variable resistance. Batteries can be considered to have memristance, but they are not passive devices. The definition of memristor is based solely on the fundamental circuit variables of current and voltage and their time integrals, just like the resistor, capacitor and inductor.
Resistor
A resistor is a two-terminal electronic component that produces a voltage across its terminals that is proportional to the electric current through it in accordance with Ohm's law which states” Voltage (V) across a resistor is proportional to the current (I) through it where the constant of proportionality is the resistance ®”.
V = IR
Resistors are elements of electrical networks and electronic circuits and are ubiquitous in most electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel/chrome).
Capacitor
A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric. When a voltage potential difference exists between the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force between the plates. The effect is greatest between wide, flat, parallel, narrowly separated conductors.
An ideal capacitor is characterized by a single constant value, capacitance, which is measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them. In practice, the dielectric between the plates passes a small amount of leakage current. The conductors and leads introduce an equivalent series resistance and the dielectric has an electric field strength limit resulting in a breakdown voltage.
Need for Memristors
Memristance (Memory + Resistance) is a property of an Electrical Component that describes the variation in Resistance of a component with the flow of charge. Any two-terminal electrical component that exhibits memristance is known as a Memristor. Memristance is becoming more relevant and necessary as we approach smaller circuits, and at some point when we scale into nano electronics, we would have to take memristance into account in our circuit models to simulate and design electronic circuits properly. An ideal memristor is a passive two-terminal electronic device that is built to express only the property of memristance (just as a resistor expresses resistance and an inductor expresses inductance). However, in practice it may be difficult to build a 'pure memristor,' since a real device may also have a small amount of some other property, such as capacitance (just as any real inductor also has resistance).
Memristors – History and Evolution
Memristor postulated in a seminal 1971 paper in the IEEE Transactions on Circuit Theory by an Electrical Engineer Professor Leon Chua at the University of California, Berkeley. The hold-up over the last 37 years, according to professor Chua, has been a misconception that has pervaded electronic circuit theory. That misconception is that the fundamental relationship in passive circuitry is between voltage and charge.
Anyone familiar with electronics knows the trinity of fundamental components: the resistor, the capacitor, and the inductor. Professor Chua predicted that there should be a fourth element: a memory resistor, or Memristor. Such a device, he figured, would provide a similar relationship between magnetic flux and charge that a resistor gives between voltage and current. In practice, it will act like a resistor whose value could vary according to the current passing through it and which would remember that value even after the current disappeared. As, Professor Leon Chua pointed out in 1971, for the sake of the logical completeness of circuit theory; a fourth passive element should in fact be added to the list. He named this hypothetical element, linking flux and charge, the ‘Memristor’. But no one knew how to build one.
Evolution
Many researchers observed and reported unusual 'hysteresis' in their current-voltage plots of various devices and circuits based on many different types of materials and structures. They were actually seeing memristance, but apparently not aware of it.
All electronic textbooks have been teaching using the wrong variables - voltage and charge - explaining away inaccuracies as anomalies. What they should have been teaching is the relationship between changes in voltage, or flux, and charge.
Without Professor Chua's circuit equations, making use of this device is not possible. It's such a funky thing. People were using all the wrong circuit equations.
Difference from other elements
The reason that the Memristor is radically different from the other fundamental circuit elements is that, unlike them, it carries a memory of its past. The Memristor changes its impedance depending on the current applied. At any given instant, a Memristor is a resistor, where V=IR. However, the application of I will change R accordingly. Dynamically, the Memristor appears as either an impulse or a charge modulated resistor. When the voltage to the circuit is turned off, the Memristor still remembers how much was applied before and for how long. This effect can't be duplicated by any circuit combination of resistors, capacitors, and inductors.
Working Analogy of Memristor
A Memristor effectively stores information because the level of its electrical resistance changes when current is applied. A typical resistor provides a stable level of resistance. By contrast, a Memristor can have a high level of resistance, which can be interpreted as a computer as a "1" in data terms, and a low level can be interpreted as a "0." Thus, data can be recorded and rewritten by controlling current. In a sense, a Memristor is a variable resistor that, through its resistance, reflects its own history. We can get it (resistance changes) with less energy. It is a large amount of resistance change with a small amount of memory.
It is essentially a device that works under alternating current (a.c.) conditions in which the applied voltage varies sinusoidally with time. As the polarity of this voltage changes, the Memristor can switch reversibly between a less conductive OFF state and a more conductive ON state. Crucially, the value of the current flow through the Memristor (the measure of its resistance) does not in the second half of the cycle retrace the exact path it took in the first. Because of this ‘hysteresis’ effect, the Memristor acts as a nonlinear resistor the resistance of which depends on the history of the voltage across it — its name, a contraction of ‘memory resistor’, reflects just that property. The Memristor is a special case of a more general class of nonlinear dynamical devices called memristive systems.