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Designing a LPF

Corner frequency of a low pass filter

Ideal & Real Filter

Low Pass Filter vs High Pass Filter

Advantages of a LPF

What are the uses of a low pass filter

FAQs

Definition of LPF:

“Low pass filter carries lower frequency signals with less resistance and has a constant output gain from zero to a cut-off frequency.”
Generally, a low pass filter does attenuation of frequencies above cut-off points.

Circuit Diagram of a Low Pass Filter:

There are two types of active filter exist, they are-

• 
  Active Low Pass Filter – consists of mostly active components like op-amp, a transistor.
  

figure 1.1 Active Low Pass Filter

• 
  Passive Low Pass Filter – consists of mostly passive components like capacitors, resistors, etc.
  

figure 1.2 Passive Low Pass Filter

How does a Low Pass Filter Work?

What does a low pass filter do?

In figure 1.1, it’s a commonly used low-pass active filter.
The filtering is commonly done by the RC network, and the op-amp is used as a unity gain amplifier. The resistor R_F(= R) is included for Dc offset.
At DC, the capacitive reactance is infinite, and the dc resistive path to ground for both terminals should be equal.
Here, all the voltages V_i, V_x, V_y, V₀ are measured concerning ground.
The input impedance of the op-amp is always infinite; no current will flow into the input terminals.

According to the voltage divider-rule, the voltage across the capacitor,

Since the op-amp gain is infinite,

Where,