Analog Circuit - what is it?

Introduction


Most electronic devices today work with analog and digital components working together.
We will focus on the analog aspect in this blog. So what is considered analog and what is considered digital? Well, there are some technical differences, but let’s begin at the beginning. To get an understanding of analog components let’s compare them to digital components. And for this let’s consider the human body. Our physical bodies would be the analog components - our muscles, organs, skeleton etc. The digital aspect of our body would then consist of the calculations we do in our brain. Some might disagree, and they might have a point, but right now we are just trying to get an idea of the two and how and why they work together so well. We humans need both the analog, our bodies, and digital, our brain, to function and so analog and digital components often work together in electronics as well. So the analog components, the physical part, are considered to be analog if they don't contain any digital aspect.

These physical analog components can be divided into the passive components and active components. The main difference between passive and active components in analog circuits is their ability to introduce energy into a circuit.
Another difference is the type of behavior they exhibit in a circuit. Passive components have a linear behavior, meaning that the relationship between the input and output signals is proportional. Active components, on the other hand, have a nonlinear behavior, meaning that the relationship between the input and output signals is not proportional. Don’t know what that means? If not, then you're in luck, because we have a blog that explains it - check it out here!

Analog circuit design is used to design and develop electronic circuits that process continuous-time signals, such as voltage, current, or sound waves, in an analog format. Analog circuit design has a wide range of applications in various industries, including telecommunications, power electronics, audio engineering, biomedical engineering, and instrumentation. Some examples of applications of analog circuit design are:

  • Amplification: Analog circuits are used to amplify signals in a wide range of applications, such as audio amplifiers, radio frequency amplifiers, and instrumentation amplifiers.
  • Filtering: Analog circuits can be used to filter out unwanted frequencies in signals, such as in audio or radio frequency filters.
  • Power management: Analog circuits are used in power management applications, such as voltage regulators, to regulate and stabilize power supplies for electronic devices.
  • Sensor interface: Analog circuits are used to interface with sensors that produce analog signals, such as temperature sensors, pressure sensors, and light sensors.
  • Data conversion: Analog circuits are used to convert analog signals into digital signals, such as in analog-to-digital converters (ADCs).

 

Passive components

In analog circuits, passive components are electronic components that do not require a power source to operate. They do not introduce energy into a circuit but instead manipulate the energy that is already present in the circuit. Examples of passive components include resistors, capacitors, inductors, and diodes. These components are fundamental building blocks of most analog circuits and are used to control the flow of current, store energy, filter signals, and perform many other important functions. We will now continue with a review of some passive components. The symbol for the given component will be shown at the start for each section.

Resistors


A resistor is a passive electronic component that is used in electrical circuits to resist the flow of electric current. Below is the symbol for a

It has the effect of reducing the amplitude of the current and voltage signals that flow through it, and is often used to regulate the flow of current in a circuit. Remember when we talked about Ohms law. Be sure to check it that blog out if you haven’t already! It is also used to dissipate energy as heat, or to provide a specific voltage drop in a circuit. We learned about voltage drops here Circuit Theory

As shown on the picture above resistors are typically represented in a circuit diagram by a zigzag symbol or by a rectangle, and are available in a wide range of values, ranging from a few ohms to several megaohms - the bigger the value for ohm the higher the resistance. They are constructed from materials that have a high resistance to the flow of electric current, such as carbon or metal alloys, and their resistance value is indicated by colored bands or by the value printed on the component itself - this is also showcased in the picture of the resistor above.

Resistors play a crucial role in many electronic circuits, as they are used to set the operating conditions for other components and to prevent damage to the circuit due to excessive current flow. A very useful tool! In fact it’s so useful that if we have a circuit with no resistance we call that a short circuit, which practically means that it most likely will produce a spark, it definitely won’t conduct a current and it also probably would fry your circuit board. So like in life, the right amount of resistance is needed! But does all resistance come from resistors? Well no. And practically, definitely not. Which takes us to the capacitors and inductors.

Capacitors

A capacitor is a passive electronic component that is used in electrical circuits to store electrical energy in an electric field. It has the effect of temporarily storing electric charge and can be used to smooth out fluctuations in a circuit, filter signals, or store energy for later use.
It’s kinda like a little storage for energy in circuits, that can be used when needed!

Capacitors are typically represented in a circuit diagram by two parallel plates separated by a gap, and are available in a wide range of values, ranging from a few picofarads to several microfarads, F. The higher value for F the higher the capacitance of the capacitors.

On some capacitors, there's a positive pin, called the anode (longer leg), and a negative pin called the cathode (shorter leg). The anode always needs to be connected to a higher voltage. If you wire it up the other way around with the cathode getting a higher voltage, then prepare for an exploding cap! And it might also smell quite bad… The symbol for these kind of capacitors is:

This is also called a polarized capacitor or a eletrolytic capacitor.
Not all capacitors expose you to this danger, as some aren’t polarized, but when they are, it's very important not to mix their polarity up! But with the capacitors that are not polarized, you can stick those in either way.


They are constructed from materials with a high dielectric constant, such as ceramics, plastic films, or tantalum, and their capacitance value is indicated by the value printed on the component itself or by its physical size.

Capacitors are used in many electronic circuits, especially in applications such as power supply filtering, signal coupling, and energy storage. They are also used in AC/DC power conversion and in applications such as radio frequency filtering, timing, and signal smoothing.
The total resistance for capacitors, and inductors, are referred to as the impedance. So you think of impedance as a word we use for the total resistance in a circuit which contains capacitors and inductors.

Inductors

An inductor is a passive electronic component that is used in electrical circuits to store energy in an electromagnetic field. It has the effect of temporarily storing magnetic energy and can be used to filter signals, store energy for later use, or generate magnetic fields.

Inductors are typically represented in a circuit diagram by a coil symbol and are available in a wide range of values, ranging from a few microhenries to several henries.

They are constructed from a coil of wire, such as copper, wound around a core made of materials with high magnetic permeability, such as iron or ferrite. The inductance value of an inductor is determined by a few things. The number of turns in the coil, the cross-sectional area of the coil, and the type of core material used are all considered for the inductance value.

Inductors play a crucial role in many electronic circuits, especially in applications such as filtering, energy storage, and the generation of magnetic fields. They are also used in applications such as power supplies, and in the design of transformers, motors, and generators. And like capacitors, these are used for wireless power transfer!

Diodes

A diode is a passive electronic component that is used in electrical circuits to allow electric current to flow in only one direction. Like a one way street! It acts as a one-way valve for electric current, and is often used to convert alternating current (AC) to direct current (DC), to protect other components in a circuit from damage due to reverse voltage, or to rectify signals.

Diodes are typically represented in a circuit diagram by a triangle symbol with a line at one end and are available in a wide range of types, including standard diodes, Zener diodes, and light-emitting diodes (LEDs). Like the capacitor the diode also has two legs, the anode and the cathode. The anode is typically connected to the + side and the cathode to the - side. 

They are constructed from semiconductor materials, such as silicon or germanium, and their forward voltage drop, which is the voltage across the diode when it is conducting current, is indicated by the type of diode and the specific application. The forward voltage is the voltage needed for the diodes to conduct a current forward, or in the direction of the arrow of its symbol. If that threshold isn't met there's no current through the diode. The reverse voltage is the voltage drop across the diode if the voltage at the cathode is more positive than the voltage at the anode (if you connect + to the cathode). So in other words, it is the voltage needed for a current to run through in the opposite direction of the arrow. This is usually much higher than the forward voltage.  

Diodes are used in applications such as power rectification, voltage regulation, and signal detection. And as mentioned earlier, they are also used in applications such as rectifying AC to DC - this is called a diode rectifier and most often consists of four diodes working together. This rectifier converts an AC-signal to a DC-signal and a basic example of the circuit and input and output is shown below, see figure 1. The red part is the symbol for an AC-generator and RL are often used to showcase the load in a circuit.

Figure 1: Illustrates the basic circuit of the full bridge rectifer.

In figure 1 we see the AC input is converted to what can be considered a DC output. We earlier talked about how capacitors can be used to smoothing a signal. Based on the output depicted in figure 1 there might be a capacitor included to do exactly that. And often such a circuit that converts the AC input to a DC output is constructed with a capacitor, see figure 2.

Figure 2: Illustrates the circuit of the full bridge rectifer that includes a capacitor to smoothing the output.

Visit this site to learn more about this rectifier.

 

Diodes are also used for generating square waves, and providing protection to other components in a circuit from voltage spikes or reverse voltage. They can act as the protectors of the other components but also bring other skills to the table as well!

 

Active Components

In analog circuits, active components are electronic components that require a power source to operate. They introduce energy into a circuit, and can control the flow of current in a circuit. Examples of active components include transistors, operational amplifiers (Op-Amps), and voltage regulators. Unlike passive components, active components can amplify signals, switch current on and off, generate signals, and perform many other complex functions. They play an important role in many analog circuits, especially in applications such as amplification, signal processing and power control. And a few active components consist of multiple components working together like we saw with the diode rectifier. 

Transistors


The symbol for a BJT, bipolar junction transistor
C stands for collector
B stands for base
E stands for emitter


A transistor is an active electronic component that is used in electrical circuits to amplify or switch electrical signals. It has the effect of controlling the flow of current in a circuit and can be used to amplify weak signals, switch high-power signals, or perform digital operations.

Transistors are available in a wide range of types, including bipolar junction transistors (BJTs) and field-effect transistors (FETs). They are constructed from semiconductor materials, such as silicon or germanium, and are typically represented in a circuit diagram by a symbol that indicates the type of transistor and the configuration in which it is being used.


Bipolar Junction Transistors (BJTs) and Field-Effect Transistors (FETs) are two different types of transistors that are used in electronic circuits. While both types of transistors perform similar functions, such as amplification and switching, there are several key differences between BJTs and FETs.
We will focus more on BJTs as we wish to display the overall function of transistors in this blog.
But here are some quick similarities and differences between the two.

 

  • BJTs have a low input impedance, while FETs have a very high input impedance.
    BJTs have a lower gain than FETs, which means that they are not as efficient at amplifying signals as FETs.
  • BJTs are polar devices, meaning that they require a specific direction of current flow, while FETs are non-polar devices and can operate with either positive or negative voltage applied to their terminals.
  • BJTs can handle higher voltages than FETs, making them more suitable for use in high-voltage circuits.
  • BJTs are slower than FETs and have longer switching times (switching time is basically how fast the component is able to react to changes in voltages).

Both BJTs and FETs have their own advantages and disadvantages, and the choice of which type of transistor to use in a particular application depends on a number of factors, including the required operating voltage, gain, input impedance, speed, and cost.

 

BJT


In a bipolar junction transistor (BJT), the flow of current is controlled by the application of a small voltage to the base terminal. This voltage controls the flow of current between the emitter and collector terminals, allowing the transistor to act as an amplifier or switch.

So a typical use for the BJT is to adjust the base current as needed. Why? What happens if the base voltage increases or decreases? Roughly, the emitter current of a BJT increases exponentially as the base-emitter voltage increases. More base-emitter voltage, regardless of the collector voltage, means more emitter current. The current that flows from C to E is called Ic.

 

Imagine that the collector is connected to some sort of voltage generator, maybe a battery and that the emitter is connected to a load - it could be anything that needs an electrical current to function. We control the current to the load by adjusting the base current! Like a valve for a faucet.

There are other types of transistors as well, such as the Junction Field-Effect Transistors (JFETs) and Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs). These two different types of field-effect transistors both perform similar functions, such as amplification and switching, but there are some key differences between JFETs and MOSFETs, which are similar to the differences between BJT and FET. But just be aware that there are many different types of transistors all for different applications!

Transistors are used to perform a wide range of functions, such as amplification, switching, digital logic (which we will cover in these blogs: digital circuits and microcontroller), and power control.

 

Operational amplifiers (Op-Amps)

        

An operational amplifier (op-amp) is a type of integrated circuit that is used as a high-gain amplifier in electrical circuits. Its main objective is amplifying small voltage signals to produce a larger output voltage and can be used for a wide range of applications, including amplification, filtering, and signal conversion.

Op-amps are typically represented in a circuit diagram by a triangle symbol with multiple input and output terminals, and are available in a wide range of types, including single-supply op-amps, dual-supply op-amps, and rail-to-rail op-amps. Through this blog we will get a basic understanding of the op-amp, so the symbol of the op-amp above, with two inputs and one output is sufficient at the moment.

They are constructed from a combination of bipolar and field-effect transistors, and are designed to operate with a very high gain and low noise.

Op-amps are used to perform a wide range of functions, such as amplification, filtering, signal conversion, and control. They are widely used in applications such as amplifiers, filters, comparators, and control circuits, and are an essential component in many analog and mixed-signal circuits. There are many different types of op-amps but as with the transistors, they all serve the same main function but for different applications.

The op-amp consists of somewhat complex circuits. So let's continue with a simple introduction of how op-amps work. We will won't discuss the circuits found within an op-amp but we will concentrate on their main functions.


So just like with the electrolytic capacitor and the diodes its important to connect the positive and negative side to the correct points in the circuit for the Op-amp. The goal is to amplify the output, Vout. Vout has an equation that explains this gain:
 

A is here the amplification value (the gain value), and for an ideal op-amp this value has no limit. What is an ideal op-amp? An ideal op-amp is a theoretical model of an op-amp that has certain ideal characteristics. In practice, no op-amp can achieve all of these ideal characteristics, but they are useful in understanding the behavior and analyzing the performance of op-amp circuits.

So when we look at the eqaution it says: The voltage Vout is the difference betweem Vin (+) and Vin (-). This mean that any difference between Vin (+) and Vin (-) is gonna yield a large output. What is large? Hmm, it is the appropiate value for a high gain hehe - let's leave it at that. (In engineering saying stuff like large, small, meduim doesn't carry much information as it is somewhat subjective, but we are just getting an understanding of op-amps so we won't define what categorizes as large, medium or small)

We are going to go through 2 basic principles for an ideal op-amp that will help us understand how and why it functions.

First principle
The principle rule is that we want the voltage for Vin (-) and Vin (+) to be equal.
In an ideal operational amplifier (op-amp), the input terminals draw no current, meaning that any current flowing into the positive (+) input terminal must flow out of the negative (-) input terminal. Therefore, in order to keep the current flow balanced and prevent any current from flowing into or out of the input terminals, the voltages at the two input terminals must be equal.
If the two input voltages are not equal, a voltage difference will appear across the input terminals, which will cause a current to flow into or out of the input terminals. This can lead to distortion in the output signal and can also cause the op-amp to behave unpredictably.
So in order to maintain the proper operation and functionality of the op-amp, it is desired that the voltages at the two input terminals be kept equal, which is commonly referred to as the "virtual short" concept.
This takes us to principle two.

Second principle
The second principle says: There's no current into the inputs. So theres no input current into Vin (-) or in Vin (+). This simplifies things as we don't have to deal with what the current going on or out of the op-amp is. So if we have something comming in and something going out we know that those two are equal. But why does this make it simpler? It is a little complex but if we know that there's no current going to either of the inputs and we know that they're the same voltage, dealing with op-amps is going to become so much easier. Trust me, bro, I'm an engineer!
Okay, so now we have covered the two first principles, which are the most important ones. If thats all we need then great. But as we are dealing with an ideal op-amp this doesn't take into account a lot of the real life issues that can occur.

Offset Voltage
In practical use Vin (-) and Vin (+) aren't always equal and the difference between them is called the Offset Voltage. This voltage is usually very small and can therefore be ignored in your calculations - all depending on the precision required for the given op-amp. But when starting working with op-amps then assuming that there's not Offset Voltage will do just fine.

Input Bias Current
And just like we said that there's no current into the inputs for an ideal op-amp, then in practical use that's usually not true either. This current it called the Input Bias Current. Just like the Offset Voltage, the value for the Input Bias Current can be ignored in the same manner, as this current usually is very small.

Slew Rate
Another thing to consider in practical use is that the amplification can't happen instantly, which we assume it does for an ideal op-amp. The reality is though that we can calculate the time for the rise or drop for these voltages, and those times are called the Slew Rate.
To sum this up, the slew rate stems from the inability of the output to produce an infinite amount of current, thereby instantaneously changing the voltage. It simply can't do that and so we might need to know the Slew Rate for our calculations depending on the precision required for the Op-amp.
 

Bandwith
The last thing to discuss for the real life issues for the Op-amp is the bandwith.
For Op-amps in AC-circuits we might run into problem with the bandwith. Once we get up to a certain frequency, our op-amp might not be able to keep it. So the calculations we make for the ideal op-amp might not match what acutally is happening because the op-amp is operating outside its bandwith. This is because the Slew Rate can't keep up with the high frequency and so it simply just doesn't work. Another op-amp with higher bandwith is then needed or maybe even a whole new solution to the problem.

Okay, this will do for the understanding of Op-amps! Op-amps are all over the place in circuits and once we have this foundational understanding of the op-amp they become easier to work with and they will certainly become incredibly helpful.

 

 

Voltage regulators



A voltage regulator is an active electronic component that is used to maintain a constant voltage level in an electrical circuit, despite changes in the load or input voltage. It is a three legged fellow. One leg for the input, one the the output and one for ground. It has the effect of stabilizing the voltage in a circuit and can be used to protect other components from over-voltage or under-voltage conditions.

Voltage regulators are available in a wide range of types, including linear regulators, switching regulators, and Zener diode regulators. They are constructed from a combination of transistors, diodes, and other components.

Linear regulators operate by controlling the current flow in a circuit to maintain a constant output voltage, while switching regulators use pulse-width modulation to maintain a constant output voltage.

Voltage regulators are widely used in applications such as power supplies, voltage reference circuits, and voltage protection circuits.


Okay, now we have a better understanding of what some analog components consist of and how they affect the voltages and currents in a circuit. You can imagine that it quickly can get somewhat complex, and that there still is much to learn! But with this introduction to analog circuit design, we are getting smarter and we can build upon that and broaden our understanding of electronics!

1 kommentar

Golu kumar

Golu kumar

Very useful topic

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