Anyone working with electronic systems or components will often find the words “analog” and “digital”. What exactly do these words mean? And how does the difference between analog and digital translate into the realm of physical circuits?
An Analog World
The physical environment in which we live is characterized by analog quantities, that is, quantities that change continuously and are not restricted to a small number of discrete values. Temperature, position, light intensity, sound waves, colors, textures – our world is full of gradations, displacements and variations that do not fit into restricted measurement systems, such as “on x off”, “small x large”, “black vs. white ”or“ soft vs. hard. ”When we use a graph to visually represent the values of these analog quantities, the curve will be smooth. The most emblematic of these smoothly varying analog curves is the sinusoid:
If the world is an analogue place, why do we hear so much about digital technology today? How can we speak of a “digital revolution” if the human experience is still fundamentally analog? It turns out that the designed systems can provide much higher performance and functionality when electrical portions of these systems store, transmit and process information using signals restricted to two values: on and off, also known as one and zero.
Although the word “digital” refers in general to systems that involve a limited set of discrete values, in the context of modern electronics, “digital” means binary. In binary calculations, the only available digits are one and zero, and this mathematical construction is translated into the electronic domain through the use of digital circuits in which the voltages are always “high” or “low”.
In typical single-ended digital circuits, a high logic signal has a voltage that is close (ideally, equal to) the circuit supply voltage, and a low logic signal has a voltage close to (ideally, equal to) the circuit grounding. Since the grounding node is the reference for all voltages in the system, we say that the low logic is 0 V. Thus, if the supply voltage for a digital circuit is 3.3 V, the electrical signals present in this circuit are would resemble rectangular waveforms that transition between 0 V and 3.3 V:
In many applications, digital storage, transmission and processing are so advantageous that electrical engineers employ digital techniques even when it creates the need for additional circuits that convert analog quantities to digital quantities and then digital quantities back to analog quantities. . We will learn more about analog to digital converters and digital to analog converters in a later chapter.
Analog and Digital ICs
Currently, a large part of the activity performed by an electronic device occurs within integrated circuits. Consequently, the difference between analog and digital circuits is rooted in the difference between analog and digital integrated circuits. If you are looking for the best practical example. A multimeter is the best example you can also check the best multimeters here.
Analog and digital ICs contain the same basic components: mainly transistors, but also diodes and passive elements. However, in analog ICs, transistors are designed to amplify or produce continuously variable signals. When we polarize a transistor, we create circuit conditions that allow it to respond properly to small changes in voltage. For example, an input stage of an IC amplifier may employ the MOSFET differential pair configuration shown below; note that the current source (IBIAS) is influencing transistors Q1 and Q2.
The next circuit, called a Colpitts oscillator, uses a biased bipolar junction transistor to generate a sinusoidal signal.
Digital ICs, in contrast, are designed to allow the input signals to turn the transistors on or off completely. While MOSFETs and BJTs are found on analog ICs, the vast majority of transistors on digital ICs are MOSFETs. Designers interconnect MOSFETs to form relatively simple circuits that implement basic Boolean logic functions, and these logic gates can serve as building blocks for higher-level digital circuits, such as flip-flops and even for extremely complex circuits, such as microprocessors.
This diagram shows a MOSFET implementation of the Boolean AND function.