Name: touch-tone filter design example
Uploaded: 2024-07-08T13:20:03.000Z
Duration: 1 min 23 s
Channel: JoVE

K12 Standards

Next Generation Science Standards

High School

Physical Science

waves-and-their-applications-in-technologies-for-information-transfer

Waves and Their Applications in Technologies for Information Transfer

HS-PS4-2

Design Example

Um engenheiro projeta um circuito para um sistema de alto-falantes com um requisito de frequência de crossover de 2 kHz, considerando a resistência do alto-falante de 8 ohms.
O design do circuito conecta uma rede cruzada a um amplificador de áudio, conectando-o aos alto-falantes do woofer e do tweeter.
O woofer, um alto-falante de baixa frequência, reproduz sinais de frequências mais baixas, enquanto o tweeter, um alto-falante de alta frequência, reproduz sinais de frequências mais altas.
O diagrama de circuito equivalente inclui um filtro RC passa-alta e um filtro RL passa-baixa, com o amplificador representado por uma fonte de tensão.
A resposta de frequência da rede crossover é determinada usando as funções de transferência para os filtros passa-alta e passa-baixa.
A frequência de cruzamento de um filtro passa-alta é inversamente proporcional ao produto da resistência e capacitância.
Por outro lado, a frequência de cruzamento de um filtro passa-baixa é diretamente proporcional à relação entre resistência e indutância.
Valores conhecidos de frequência de crossover e resistência do alto-falante são usados para calcular os valores de capacitância e indutância.
Este design direciona frequências acima de 2 kHz para o tweeter e aquelas abaixo de 2 kHz para o woofer.

 resposta de frequência

A inovação da telefonia por tom de discagem revolucionou a indústria de telecomunicações ao substituir o dial rotativo tradicional por um sistema de sinalização multifrequencial de tom duplo (dual-tone multi-frequency, DTMF, em inglês). Este sistema utiliza um teclado tipo matriz com botões dispostos em quatro linhas e três colunas, criando 12 sinais distintos, cada um atribuído a um par de frequências. Cada pressionamento de botão resulta na geração simultânea de dois tons senoidais – um de um grupo de baixa frequência (697 a 941 Hz) e outro de um grupo de alta frequência (1209 a 1477 Hz).

Este sistema de tom duplo é um avanço no design da interface do usuário e uma aplicação sofisticada da tecnologia de processamento de sinal. A filtragem de sinais, conforme representado no exemplo do aparelho telefônico de tom, utiliza uma combinação de filtros passa-baixa (LP) e passa-alta (HP), seguidos por filtros passa-banda para discernir tons individuais dentro das frequências agrupadas. Os filtros passa-banda desempenham um papel fundamental na detecção de sinal, permitindo a passagem apenas de uma banda estreita de frequências – isolando efetivamente os tons produzidos pelo teclado.

O projeto desses filtros envolve eletrônica de precisão e pode ser exemplificado pela construção de um circuito RLC em série, que opera como um filtro passa-faixa. Este é um circuito ressonante composto por um resistor (R), um indutor (L) e um capacitor (C), que permite passar uma faixa seletiva de frequências enquanto bloqueia outras.

O sistema de discagem por tom exemplifica a aplicação prática do projeto de filtro eletrônico em sistemas do mundo real, mostrando a natureza crítica da seleção de frequência e da clareza do sinal na tecnologia de comunicação. Através do design meticuloso dos filtros passa-banda RLC, os telefones de tom podem interpretar com segurança as entradas do usuário, mantendo assim a integridade das informações transmitidas pelas vastas redes que conectam chamadas em todo o mundo.

 Resposta de Frequência

Um engenheiro projeta um circuito para um sistema de alto-falantes com um requisito de frequência de crossover de 2 kHz, considerando a resistência do alto-falante de 8 ohms.
O...

Education

JoVE Core

Electrical Engineering

Engenharia Elétrica

Unit 1

Unidade 1

Frequency Response

Resposta de Frequência

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

touch-tone filter design example

Touch-tone telephony uses dual-tone multi-frequency (DTMF) signaling and a filter design example to show how keypad tones are separated. It replaced the old rotary dial with a matrix-style keypad arranged in four rows and three columns. Each of the 12 buttons produces a unique signal pair.

Every key press creates two sinusoidal tones at the same time. One tone comes from a low-frequency group between 697 and 941 Hz. The other comes from a high-frequency group between 1209 and 1477 Hz. This dual-tone method is a practical example of user interface design and signal processing in telecommunications.

The system also shows how filters can isolate signals. A combination of low-pass (LP) and high-pass (HP) filters helps separate the tone ranges. Bandpass filters then detect individual tones inside those grouped frequencies. A bandpass filter passes only a narrow range of frequencies, so it can isolate the keypad tones.

The filter itself can be built as a series RLC circuit. This resonant circuit uses a resistor (R), inductor (L), and capacitor (C) to pass a selective range of frequencies while blocking others. In touch-tone telephones, this kind of electronic filter design helps the system read user input clearly and keep communication signals accurate across phone networks.

Touch-Tone Filter Design Example

network function of a circuit

How Transfer Functions Shape Circuit Response

Transfer functions show how a circuit responds as signal frequency changes. They describe the link between input and output in frequency response analysis. This makes them useful for studying how circuits behave in electronics and engineering. A transfer function is a mathematical tool that relates phasor output to phasor input. It can be written as voltage gain, current gain, transfer impedance, or transfer admittance. The poles and zeros are the most important parts of the function. Zeros...

frequency response of a circuit

Inductive Circuit Frequency Response

Inductive circuit frequency response shows how a circuit with an inductor reacts to different frequencies. The analysis starts in the time domain and then moves into the frequency domain. In that step, the inductor is replaced by an impedance, and the circuit is written with phasors, which are sinusoidal signals shown with magnitude and phase. The transfer function describes how the output changes compared with the input at each frequency. A key parameter is the time constant, which is the...

gain

Circuit Gain and Phase Shift

Circuit gain and phase shift describe how a linear circuit changes a sinusoidal input voltage or current. These properties matter in circuits with reactive elements, because the response depends on the input frequency. As the frequency changes, the gain and phase shift also change. Gain compares the size of the output sinusoid to the size of the input sinusoid. If Vin is the input and Vout is the output, the gain K is the ratio of the output amplitude to the input amplitude. A gain greater...

bode plots

Reading Frequency Response on Bode Plots

Bode plots show how a circuit or system responds across frequency. They use a logarithmic frequency scale on the x-axis and gain in decibels on the y-axis. This format makes it easier to display a wide range of frequencies and to see how circuit parts affect behavior over that range. A network function gives the ratio of output to input for a system. Its complex form provides both magnitude and phase angle. The logarithmic gain on a Bode plot comes from the magnitude, calculated by multiplying...

transfer function and bode plots-i

Transfer Function Gain and Origin Effects

Transfer function gain and poles or zeros at the origin shape a system's Bode plot. The transfer function is often written in standard form after the polynomial coefficients are normalized. In that form, the constant gain, zeros, poles, and quadratic terms all appear clearly. The poles and zeros mark critical frequencies where the output magnitude and phase change noticeably. The constant gain K creates a fixed magnitude and phase term. Its magnitude is 20 log 10 K in decibels, and its phase...

transfer function and bode plots-ii

Bode Plot Slope and Phase Changes

Bode plots show how a transfer function changes with frequency. The standard form includes constant gain, poles and zeros at the origin, simple poles and zeros, and quadratic poles and zeros. Each part shapes the system response in a different way. A simple zero sets the magnitude trend first. The Bode magnitude plot stays flat at low frequencies, near 0 dB, and then rises at 20 dB per decade after the corner or break frequency, ω1. That corner frequency is where the straight-line...

bode plots construction

Reading Frequency Response with Bode Plots

Bode plots show the frequency response of a system with a magnitude plot and a phase plot. Both plots use a logarithmic frequency axis. In control system analysis, this makes it easier to see how a transfer function changes with frequency. To build a Bode plot, start with the transfer function H(ω). After normalization, the function includes constant gain, zeros, and poles. Each term affects the plot in a different way. A constant gain of 10 gives a starting magnitude of 20 dB, since 20...

series resonance

Series Resonance in RLC Circuits

Series resonance in an RLC circuit happens when the inductive reactance and capacitive reactance are equal. An RLC circuit contains a resistor, an inductor, and a capacitor. The impedance of the circuit is the ratio of the supply voltage to the circuit current. At resonance, the imaginary part of the impedance becomes zero. The frequency at which this occurs is called the resonant frequency. It depends on the inductance (L) and capacitance (C) of the circuit. Mathematically, the resonant...

characteristics of series resonant circuit

characteristics-of-series-resonant-circuit

Series Resonance and RLC Filter Behavior

Series resonance in an RLC circuit happens when the inductor, capacitor, and resistor are connected in series. At the resonant frequency, the inductive reactance and capacitive reactance are equal in size but opposite in sign, so they cancel each other. As a result, the circuit impedance becomes very small and is mainly set by the resistance. The resonant frequency of a series RLC circuit can be calculated from its inductance and capacitance. At this frequency, the current reaches its maximum...

parallel resonance

Parallel RLC Tuning at Resonance

A parallel RLC circuit uses a resistor, inductor, and capacitor connected to the same nodes. Because they share the same voltage, the circuit is analyzed with admittance, which describes how easily current can flow. In a parallel RLC circuit, admittance helps show how the circuit responds as the frequency changes. Resonance happens when the net reactance is zero. At that point, the capacitive and inductive effects cancel each other out. The resonant frequency is found from this condition. At...

frequency response of op amp circuits

Op Amp Gain and Bode Plot Basics

Operational amplifiers are used for signal conditioning, filtering, and mathematical tasks such as addition, subtraction, integration, and differentiation. Their frequency response shows how amplifier gain changes as the input frequency changes. This makes the gain of an op-amp a key idea in circuit design. At low frequencies, an op-amp can hold a constant gain called the dc gain, A0. As frequency rises, the gain starts to drop after the corner frequency, or break frequency, ω1. In other...

passive filters

Audio Frequency Control with Passive Filters

Passive filters shape the frequency spectrum of electrical signals. They use only passive parts such as resistors, inductors, and capacitors. Because they do not need an external power source, they can let selected frequency ranges pass or block others in many applications. Low-pass filters pass signals below the cutoff frequency, ωc, and reduce signals above it. In audio systems, they can send bass frequencies to woofers or subwoofers. For an RC low-pass filter, the transfer function H(s)...

active filters

Active Filter Design and Frequency Response

Active filters use op-amps, resistors, and capacitors to shape a signal's frequency response. They remove unwanted frequency components while keeping the parts of the signal that are needed. The design depends on the choice of resistor and capacitor values, which set the cutoff points and help define the overall response. A first-order low-pass active filter passes signals below a cutoff frequency and reduces signals above it. Its transfer function includes the low-frequency gain, also called...

scaling

Circuit Component Scaling for Filters

Circuit component scaling helps turn simple circuit values into practical ones for filter design and circuit analysis. Engineers often start with standard values like 1 ohm, 1 henry, or 1 farad because they make examples and problems easier to work through. Later, those values can be scaled to more realistic levels. This method is useful in filters, resonant circuits, and many other circuit analysis problems. It reduces calculation complexity while keeping the circuit behavior easy to study.

design example

Touch-tone telephony uses dual-tone multi-frequency (DTMF) signaling and a filter design example to show how keypad tones are separated. It replaced the old rotary dial with a matrix-style keypad arranged in four rows and three columns. Each of the 12 buttons produces a unique signal pair. Every key press creates two sinusoidal tones at the same time. One tone comes from a low-frequency group between 697 and 941 Hz. The other comes from a high-frequency group between 1209 and 1477 Hz. This...

key terms and concepts

Explore how touch-tone phones use DTMF signaling, LP and HP filters, and a series RLC bandpass circuit to detect keypad tones clearly.

Touch-Tone Filter Design Example | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

HS-PS4-5

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HS-PS4-3

Touch-Tone Filter Design Example

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