Module 3: Electrical Fundamentals II - Filters

A filter is an electronic circuit that allows certain frequencies to pass through while blocking others.

The main types of filters are low-pass, high-pass, band-pass, and band-stop filters.

A low-pass filter allows low frequencies to pass through but blocks high frequencies.

A high-pass filter allows high frequencies to pass through but blocks low frequencies.

A band-pass filter allows a specific range of frequencies to pass through while blocking both lower and higher frequencies.

A band-stop filter blocks a specific range of frequencies while allowing both lower and higher frequencies to pass through.

The cut-off frequency is the dividing line between the frequencies allowed to pass and those blocked by a filter.

Filters separate audio signals into different frequencies, allowing different speakers to play specific ranges: high frequencies for tweeters, mid-frequencies for mid-range, and low frequencies for woofers.

A circuit that allows low-frequency signals to pass through while attenuating or reducing high-frequency signals.

The frequency at which the output voltage of a filter is 70.7% of the input voltage. This is also known as the half-power point.

A low pass filter comprised of a resistor (R) and a capacitor (C) in series. The output voltage is taken across the capacitor.

Opposition to the flow of alternating current (AC) caused by a capacitor. XC is inversely proportional to frequency.

A low pass filter comprised of a resistor (R) and an inductor (L) in series. The output voltage is taken across the resistor.

Opposition to the flow of alternating current (AC) caused by an inductor. XL is directly proportional to frequency.

The reduction in the amplitude of a signal as it passes through a circuit.

RC low pass filters are generally easier to use, more cost-effective, and provide similar functionality compared to RL low pass filters.

Inductors introduce resistive loss, meaning some energy is lost as heat during operation. Capacitors, on the other hand, do not have this inherent loss.

A high pass filter allows high frequencies to pass through while blocking low frequencies. Both RC and RL circuits can be used to create high pass filters.

In an RC high pass filter, the capacitor has a high reactance at low frequencies, blocking the signal. At high frequencies, its reactance decreases, allowing the signal to pass through to the output.

In an RL high pass filter, the inductor has a low reactance at low frequencies, allowing the signal to pass through. At high frequencies, its reactance increases, blocking the signal.

Resonance occurs in an LCR circuit when the inductive reactance (XL) and capacitive reactance (XC) are equal. This happens at a specific frequency determined by the values of L and C.

A resonant circuit, where XL equals XC, is known as a tuned circuit. These circuits are designed to operate effectively at specific frequencies.

Resonant circuits, like series-LC and parallel-LC, act as filters by selectively allowing or blocking specific frequencies of current.

A series-LC circuit acts as a band-pass filter, minimizing opposition to current flow at its resonant frequency and maximizing it for other frequencies.

A parallel-LC circuit functions as a band-stop filter, maximizing opposition to current flow near its resonant frequency and minimizing it for other frequencies.

A band-pass filter allows a specific range of frequencies to pass through while blocking frequencies outside that range.

A band-stop filter blocks a specific range of frequencies while allowing frequencies outside that range to pass through.

You can combine a series-LC circuit (band-pass) and a parallel-LC circuit (band-stop) to create a simple band-pass filter.

The upper and lower frequency limits of a band-pass or band-stop filter are known as cutoff points. These points determine the edges of the filter's action.

Filters are crucial in electronics for various applications. They can shape audio signals, isolate different frequencies in radio communication, and protect circuits from unwanted signals.

The frequency at which the inductive reactance (XL) and capacitive reactance (XC) in an LCR circuit have equal magnitudes. At this frequency, the circuit behaves as purely resistive.

Below the resonant frequency (fr), capacitive reactance (XC) is greater than inductive reactance (XL), making the circuit act capacitively. This means the circuit impedes the flow of high frequencies more than low frequencies.

Above the resonant frequency (fr), inductive reactance (XL) is greater than capacitive reactance (XC), resulting in inductive behavior. This means the circuit impedes the flow of low frequencies more than high frequencies.

The resonant frequency (fr) of an LCR circuit is calculated as 1/(2π√(LC)), where L is inductance and C is capacitance.

Increasing the inductance (L) or capacitance (C) in an LCR circuit decreases the resonant frequency (fr), while decreasing L or C increases fr.

A parallel LCR circuit also exhibits resonance, where the resonant frequency (fr) is calculated using the same formula: 1/(2π√(LC)).

A radio tuner uses a tuned LCR circuit to select a specific radio station's frequency, allowing you to listen to it and reject others.

A simple band-stop filter is typically made of two resonant circuits: a parallel LC circuit and a series LC circuit tuned to the same frequency. The parallel LC circuit acts as the band-reject filter, while the series LC circuit provides a bypass for the rejected frequencies.

A band-stop filter blocks a specific range of frequencies, while a band-pass filter allows only a specific range of frequencies to pass through. They are essentially opposites.

A band-stop filter is also known as a band-suppression filter or a band-reject filter.

The center frequency (fr) of a band-stop filter is the frequency at which the minimum amount of current flows through the filter. This is the frequency that is being blocked.

The lower cut-off (f1) and upper cut-off (f2) frequencies define the boundaries of the rejected frequency band. Frequencies below f1 and above f2 are allowed to pass through the filter.

Band-stop filters are used in various applications, including:

1. Radio receivers: To eliminate unwanted frequencies from interfering with the desired signal.
2. Audio systems: To remove unwanted frequencies that can cause distortion or feedback.
3. Power systems: To block frequencies that can damage electronics.
4. Medical equipment: To filter out unwanted frequencies that can interfere with diagnostic signals.

A band-stop filter is specifically designed to remove or block a specific band of frequencies while allowing other frequencies to pass through.