Understanding how filter circuits work is an important topic in electronics. It serves as a very important piece of the puzzle. Wherever we go, whatever we do, everywhere we come across one thing for sure. Noise, noise, noise, noise, noise...
Yes, in real life, I have no idea of how to deal with this noise other than trying to ignore it. That also try only.
But in electronics, that's not the case. We can eliminate the noise or control it however we want using this filter circuits.
One thing I like very much in electronics is that we can control the outcome as much as possible based on whatever we want. Coming back to the topic.
Filters play a major role in analog circuits, not only in that even in power circuits, we will use filter circuits to eliminate ripples. Its having a wide range of applications. Basically is we use it to eliminate the unwanted signal or amplitude in our desired signals. In one word, eliminate the NOISE.
So, to understand the working of filters, one must understand the two basic electronic principles.
1. Voltage drop across the divider circuit. Yes, a filter is basically a voltage divider
2. Response of RLC components with respect to frequency.
To illustrate the second point, the resistance of the resistor stays constant irrespective of the change in frequency. But in the case of capacitors and inductors, that's not the case. For AC signals, the reactance of the capacitor decreases with an increase in frequency, and the reactance of the inductor increases with an increase in frequency. That's why it's called reactance.
The equation for reactance looks like below.
Capacitive reactance, `X_{C}=\frac{1}{2\pi fC}`
Inductive reactance, `X_{L}=2\pi fL`
Where
`f`-frequency
`C`- Capacitance of the capacitor
`L`- Inductance of the inductor.
So from the above equations, we can see that the reactance of the capacitor is inversely proportional to frequency(`X_{c}\propto\frac{1}{F}`), and the reactance of the inductor is directly proportional to frequency(`X_{L}\proptoF`).
This proves the point that an ideal capacitor offers an infinite resistance to the DC signal as frequency content is zero in DC and an ideal inductor offers infinite resistance to the AC signal (i.e high frequency AC signals).
The filter circuit is all about playing with the reactance offered by this capacitor and inductor to the AC signals. So simple, right?
There are basically four types of filters. Of course, there are many types. But first, we will see these four types, and then we will look into others. Basic first, always.
Low Pass--->Passes low frequency signals
High pass--->Passes high frequency signals
Band pass-->Passes certain range(band) of frequency signals
Band rejection-->Blocks certain range(band) of frequency signals
There are a few terminologies we should know when we are working with filters.
- Bandwidth--> how much range the filter can effectively filter out signals
- DB levels-->Amplitude will be normally indicated in terms of DB(decibel)
- Blot plot-->Graphs used to visualise the effectiveness of the filters.
That's it. We now know the minimum basics about the filter circuit to start working with it.
With this, we can dive deep into the workings of every filter and my favorite part of their derivations and equations for the calculations. Lets go...
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