Investigating The Fourth Passive Component

When first learning about and building electronic circuits, the first things all of us come across are passive components such as resistors, capacitors, and inductors. These have easily-understandable properties and are used in nearly all circuits in some way or another. Eventually we’ll move on to learning about active components like transistors, but there’s a fourth passive circuit component that’s almost never encountered. Known as the memristor, this mysterious device is not quite as intuitive as the other three, so [Andrew] created an Arduino shield to investigate their properties.

Memristors relate electric charge and magnetic flux linkage, which means that their resistance changes based on the current that passes through them. As their name implies, this means they have memory, and retain their properties even after power is removed. [Andrew] is testing three different memristors, composed of tungsten, carbon, and chromium, using this specialized test set. The rig is based on an Arduino Uno and has a few circuit components that can be used as references and generates data on the behavior of the memristors under various situations.

The memristors used here do exhibit expected behavior when driven with positive voltage signals, but did exhibit a large amount of variability when voltage was applied in a negative direction. [Andrew] speculates that using these devices for storage would be difficult and would likely require fairly bespoke applications for each type. But as the applications for these seemingly bizarre circuit components increase, we expect them to improve much like any other passive component.

45 thoughts on “Investigating The Fourth Passive Component

      1. A factually correct, yet useless comment that took up a “page” of my time (think about it…0K)

        Memristors are not a base component, they are jsut a lumped component comprising RCL’s.

    1. Diodes and their cousins, light emitting diodes.

      Speaking of LEDs, there’s another important component missing – the light bulb/incandescent lamp.

      It can be used as a current-limiting device, similar to a resistor. A negative resistor, so to say.

      By installing a 12v halogen lamp in series with a power supply and a 12v rechargeable battery (say, lead-gel) you have an automatic charger circuit.

      An incandescent lamp can also act as a fuse, for both DC and AC.
      In the famous FT-101 transceiver, there’s a little incandescent lamp on the receiver input, for protecting the receiver from thunder.

        1. It had not occurred to me until I saw your comment, but a incandescent light is a resistor with short term memory. It seems like you could build a visual dram teaching tool with one, periodically reading its resistance and refreshing its state.

      1. As I posted only yesterday, my crude picture is that “passive” means anything that can appear in a circuit by accident – resistors, capacitors, inductors, antennae, switches etc. Why people include diodes, I don’t claim to understand.

          1. They are not passive as they have turn on voltage, when forward Bias the depletion layer reduces until the point of conduction, this could be 150mV 200mV 400mV 700mV depending on the material. LED over 2V. Tunnel Diodes, have a negative slop, so can form an oscillator circuit well into the GHZ, I would not call them passive.

      2. Not so sure about the linearity requirement. Most things in nature are non-linear, and we go to great pains when fabricating things like resistors to choose materials that behave mostly linear over their operating range simply because linearity simplifies design.
        E.g., an incandescent lightbulb is a very non-linear resistor.

    2. Diodes are considered passive because they don’t amplify, but there’s the tunnel diode that has negative resistance over part of it’s V/I curve, and was used as the active device in oscillators in the 1960s, when it could oscillate at higher frequencies than then-available transistors.

    3. Except for tunnel diodes, lambda diodes and several others which are actually active components. Even varactors if external pumping is allowed.
      (If we define as active components which are able of power gain)

      1. “Requiring” power to operate, and “consuming”, or “dissipating”, power–either real power or reactive power (R + jX)–are two completely unrelated physical concepts. You cannot compare the two; they are totally and completely unrelated.

  1. You set the resistance by running a current through it. Remove power and the resistance remains. Ok. But how do you measure that “remembered” resistance without sending current through again thus changing it?

    I don’t get it.

    1. Let me explain in a very simple way, by using a cube on half-pipe (you know, the tube kids use for skateboards) as an example for the memristor effect. The cube is in the center of the halfpipe. Now please correct me if I’m wrong, but this is the way I like the envision memristors.

      Pushing against the block is voltage. The position on the pipe is the resistance, which goes down when you go up. So you require effort to push it up and since it’s a cube it doesn’t roll down, it stays to the point where you pushed it. If you want to lower the resistance, push the block down by using negative voltage (push the block from the other side) it will no go to a lower resistance until it goes to the other side of the pipe where it goes up again. This allow you to set reset the block position/resistance of the memristor.
      Reading the position is simply applying a voltage low enough that you don’t change the position of the block. In other words, the reading voltage/current has to be lower than the driving and you’ll be fine.

  2. How can you use a resistor or inductor or capacitor without putting power into it?
    How is a capacitor not a memory device? They’re at the ‘core’ of DRAM.
    Boost converters (the architecture; not the function) have obviously separate ‘storage’ and ‘recall’ phases for their inductors.
    If I just need two leads to be called passive, then a diac is passive, too (and exhibits memory).

  3. The reason this is considered the fourth fundamental element is because resistors exhibit a voltage vs current behavior, capacitors exhibit a voltage vs charge behavior, inductors exhibit a current vs magnetic flux behavior, and memristors exhibit a charge vs magnetic flux behavior.
    Diodes, lightbulbs, and diacs are weirdo resistors.

  4. Practical questions occur ..

    Capacitors and inductors both can store energy, which is another way to say they have state. Resistors don’t store energy, and are stateless. Where does this nifty memristor fit, in that regard?

    Also, the equations give the impression that a steady state current, which is a non-zero dq/dt, should cause a steadily increasing flux? That seems absurd. Guess I need that one explained a bit more.

    An inductor is kind of like a resistance that changes depending on the history of the voltage you put across it; a capacitor like a resistance that changes depending on the history of the current you put through it. Guessing a memristor is like a resistance that changes depending on .. what now? Looked at that way, where does it fit?

    Where can anyone find a simple explainer for what these do in a circuit?

  5. The difference between active and passive is whether or not an energy (electrical) source is required to operate. Active devices are devices that require an energy (electrical) source for signal amplification, conversion, etc., such as ICs and modules. Passive devices are devices that do not require an energy (electrical) source for signal transmission or directional “signal amplification” devices, such as capacitive, resistive, inductive and so on. Active devices generally output a set of 4 ~ 20mA signal loop, passive devices do not have a power supply loop.

    Maybe there’s an answer here that you’d like to know:

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