How an Analog Signal is converted Into a Digital One (Part l)

From your keyboard to a letter in the screen

We all know that technology has helped us in more ways than we can imagine, to the point where now we can't even picture our lives going forward without It. However, for most of us, Its functioning is akind to sorcery as to how our devices can interact with the external world and produce something coherent. In this little article I will provide you with an understandable base as to how those subtle signals that come from a physical stimuli, once transformed into electrical signals (Analog), can be transformed to something that the computer can understand and work with, all with a particular method: Succesive Approximations, explaining the components behind a common circuit, how they interact and what happens at the end. Let's begin by explaining what an Ideal ADC or Analog to Digital Converter is:

What an ADC is?

An Analog to Digital Converter is an electronical device used to transform a particular Analog Signal (which varies in a continuous way), such as an AC electric signal, into a Digital Sequence of Data that more or less accurately reflects what the original signal contains, all through the take of samples from It, then quantifying and codifying them in the final digital word (Processes which I will explain in a separated article).

Now that we know what the main purpose and goal of an Analog to Digital Converter, we can explain further how the process of conversion through successive approximations work, not without having prior knowledge of Its main parts, which can be seem in the next image:

Digital to Analog Converter:

As Its name suggest, Its main purpose is to convert a Digital Input into an Analog one, with a determined number of inputs that are equivalent to a digital sequence of that length, having just one output, due to the fact that what comes out is in analog form. It usually composes of an Amp.Op in closed loop paired with resistors. You might ask why a Digital to Analog Converter is used If we want to pass an Analog Signal to the digital plane. Well, It is because we will use this Converter coupled with a comparator to verify if our input signal is greater than the Analog signal that the SAR asks for the DAC to convert and generate the whole digital word.

Comparator

It is an Integrated circuit, generally an Amp.Op with open loop, used to compare two input signals, one acting as a reference, being a fixed tension and the other one as a variable voltage to determine which one is greater or lesser, thus varying the output according to the results obtained.

Successive Approximation Register

The Brain of the whole system. This register is the main part of the reference input that comes into the comparator, as It will generate a particular sequence of data (In Digital form) that the DAC will convert into an electric signal that will go to the comparator and the latter will determine if It has a higher or lower value than the analog input, responding to any possibility in a different way. It has three terminals connected to It. One, called Start of Conversion, Is the one that will determine when the process of Analog to Digital conversion will begin. The second is denominated as End of Conversion, being self explanatory in the fact that with It we will indicate when the conversion will end. And then, a third control input, Clock, which will be used as a mean to establish how much It will take for the whole circuit to complete the conversion.

Now that we know all the components used in an ADC converter, with their particular functions, in the next article of this series we'll explain, both as an analogy and in technical terms, how the whole circuit operates, from the actions of comparing the reference signal generated and the input that comes into the comparator, to how the successive approximation register generates the digital data for the DAC to convert into a signal with which to equal the input. As always, thanks you for your support and Good Luck!