IBM Creates Ring Oscillator on a Single Nanotube

deeptrace writes "IBM has combined CMOS circuitry and a single carbon nanotube to implement a 5 stage ring oscillator. Even though the oscillator runs at just 52 MHz, they expect that it could reach the GHz range with improvements. The frequency of the current oscillator was higher than previous circuits using multiple nanotubes. IBM describes the achievement in the paper "Integrated Logic Circuit Assembled on a Single Carbon Nanotube" to be published this week in the journal Science."

Comments

A what?

[Eightyford]

What the hell is a ring oscillator, you ask? Well, wikipedia says:

A ring oscillator is a device composed of an odd number of NOT gates whose output oscillates between two voltage levels, representing true and false. The NOT gates, or inverters, are attached in a chain; the output of the last inverter is fed back into the first. The simplest ring oscillator, then, is a single inverter whose output is fed back to itself. Because a single inverter computes the logical NOT of its input, it can be shown that the last output of a chain of an odd number of inverters is the logical NOT of the first input. This final output is asserted a finite amount of time after the first input is asserted; the feedback of this last output to the input causes oscillation.

A circular chain composed of an even number of inverters cannot be used as a ring oscillator; the last output in this case is the same as the input. However, this configuration of inverter feedback can be used as a storage element; it is the basic building block of static random access memory, or SRAM.

A real ring oscillator only requires power to operate; above a certain threshold voltage, oscillations begin spontaneously. To increase the frequency of oscillation, two methods may be used. Firstly, the applied voltage may be increased; this increases both the frequency of the oscillation and the power consumed, which is dissipated as heat. The heat dissipated limits the speed of a given oscillator. Secondly, a smaller ring oscillator may be fabricated; this results in a higher frequency of oscillation given a certain power consumption.

To understand the operation of a ring oscillator, one must first understand gate delay. In a physical device, no gate can switch instantaneously; in a device fabricated with MOSFETs, for example, the gate capacitance must be charged before current can flow between the source and the drain. Thus, the output of every inverter of a ring oscillator changes a finite amount of time after the input has changed. From here, it can be easily seen that adding more inverters to the chain increases the total gate delay, reducing the frequency of oscillation.

Microsoft Innovates Too!

[BBCWatcher]

I'm really offended by all this IBM boosterism at Slashdot. Didn't you all hear Steve Ballmer say that IBM doesn't innovate? He's right, you know. And this carbon nanotube business is yet more evidence. IBM's work is hardly original. Carbon has been around forever. Steve Ballmer himself is made of carbon and other elements.

Now let's talk about REAL innovation. Microsoft just announced a new facial feature pack for Office's "Clippy." Now you can customize Clippy according to your facial preferences. Options include complexion, hair style, nose shape and size, and ear/nose jewelry.

Re:Can you please explain why this is significant?

[eurowombat]

Ring oscillators are simple circuits with which you can easily compare different circuit technolgoies. You simply scale the circuit to whatever your new design rules are, say 90 nm -> 65 nm, soi, etc. and measure the new frequency of the oscillator. This gives you a good base point for measuring and comparing the performance of the new technology.

Re:Explanation?

[jedZ]

A 5-stage ring oscillator is the hardware equivalent of a program that displays 'Hello World!'

Odd... just did this in class today...

[jpardey]

Lets see if this helps. Some people were confused...

A ring oscillator is a device for making square waves. It uses a common component, a NOT gate. In digital logic, there are two levels, high and low (or 1 and 0, respectivly). High is usually, as far as I have seen, +5 volts, while low is 0 volts (ground).

A NOT gate simply inverts the input. If the value is 1, it outputs 0. If the value is 0, it outputs 1. If the value is somewhere between the two, it will choose one state or the other based on some threshold voltage.

Changing output is not instantaneous. How much time it takes, I don't know. However, it is very fast.

I was going to draw a schematic, but I gave up on appeasing the lameness filter. So, we will use the power of imagination! Imagine one of these NOT gates hooked up to itself. It will switch on and off at a terrific rate. Put a wire on the output, and you have a square wave! Want it slower? Take another two NOT gates, and put them in the loop, so that the first one goes to the second goes to the third. Slower? Another two. If the number of NOT gates was even, the inverted signal would be uninverted by the next NOT gate, which is not what we want.

For more control, one can use a capacitor in a certain arrangment (I'm not looking through my notes). It will take a while to charge and discharge, acting as a delay. Just don't read its voltage as the signal, or you will get a dropping bit, then a rising bit, rather than a nice clean square wave.

Quite useful devices. I hope this clarifies things.