# Memristor basics | What is Memristor | Properties

This page covers memristor basics including its definition.
It also mentions memristor analogy and properties of a **memristor**.

As we know there are three two terminal circuit elements viz. resistor, capacitor and inductor.
These are defined in terms of relation between two circuit variables out of four viz. current (i),
charge (q), voltage (v) and flux (φ). The current is defined as time derivative of charge (i.e. dq/dt) while
voltage is defined as time derivative of flux(i.e. dφ/dt).

➨Resistor is defined by relation between voltage and current i.e. dv = R*di

➨Capacitor is defined by relation between charge and voltage i.e. dq = C*dV

➨Inductor is defined by releation between flux and current i.e. dφ = L*di

The element known as memristor (short form of memory resistor) provides relationship between
charge and flux i.e. dφ = M*dq.

Here M is memristance.

The figure-1 depicts four basic circuit elements viz. resistor, capacitor, inductor and memristor.

**Memristor definition**:

The term Memristor is a passive device which provides functional relation between charge and flux.
It is defined as circuit element in which flux(φ) between two terminals is function of amount of
charge(q) passed through the two terminal device. It is not energy storage element.
The figure-2 depicts symbol of a memristor.

The device memristor is known as charge controlled device when relationship between flux and charge is represented
as function of electric charge (q) i.e. φ = f(q)

It is known as flux controlled memristor when relationship is expressed as function of flux linkage i.e.
q = f(φ)

## Memristor Properties

• The memresistance is property of a memristor. The resistance of memristor increases when charge flows in
one direction and decreases when it flows in the opposite direction.

• When the applied voltage is switched off,
charge flow will get stopped and memristor will remember its last resistance.

• When flow of charge is started again, the device will have resistance equal to the value when
it was last active.

• The resistor is analogous to pipe through which water flows while memristor is a different kind of pipe
whose diameter increases or decreases based on direction of water flow through it.

•
The figure-3 depicts curves (φ-q) or characteristics of a memristor device. As memristor is purely dissipative, it acts like
resistor. The φ-q curve of memristor is always monotonically increasing function.

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