Question: Which component in a computer is the ADC?

Asked Quora & sample the result

This week, we had a question pop up on Quora about analogue to digital conversion. The poor questioner had confused the role of Power from the AC wall socket and signals.

I have to admit to being somewhat surprised by that. It’s one of those few situations where you are so used to something being the way it is, you forget that not everyone understand it.

“Alternative Current

The voltage out of a wall socket is alternating current. If you measure the current across the wires (for goodness sake don’t!) you’ll typically see the following graph (sinusoidal)

V_max and V_min as well as t or \theta depend on your country’s household voltage supply (or industrial supply) and frequency respectively. AC current from the wall plugs into your power supply on the back of your PC or into the laptop supply. That get changes into DC current through a two step combination of step-down Transformer, Full Wave [Bridge] Rectified and a regulator circuit to take it down from, say, 110v to the 12v your PC uses. Whilst the signal is analogue, and it’s an analogue electronics circuit, it isn’t used to transfer information. More on this later, but you have to remember this is about power.

Analogue-to-Digital Conversion & Converters (ADC)

ADC’s transform an analogue signal to digital value through a series of samples. This is the same process which converts audio from a mic to CD or MP3 music. It is typically sampled at 16-bit or more, to give a good breadth of value to use and those sample values are what are passed along to another device.

Samples are periodically taken to measure the value of the analogue signal and that sample is then converted into the digital signal. Each black vertical line in the below image is a sample.

As you can see from the image, the reconstructed signal is not exactly the same as the original signal. There is some loss. The less you sample, the more loss it has. Also the lower the bit-width, the more loss it has.

Unlike AC current, this is about signals, not power. This is like plugging in a mic to your PC, your sound card (which stores one of the few ADC’s in a computer) samples and converts it to a digital signal and puts it on the internal data bus.

I hope you can see why they are both different things.”

Ethar is a Lean-EA and director of Axelisys. He works to make organisations more productive and has been involved in the agile space since 2002. Yet, unlike many, he is still very much a “hands-on” techie. If you found this article useful, hit-the-heart and share the knowledge.