Capítulo 1 - Introdução à Eletrônica

PowerPoint Overheads for
Sedra/Smith
Microelectronic Circuits 5/e
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Introduction to Electronics
3
Sinal: todo meio que contenha informações de interesse.
Exemplo:
Informações sobre o tempo:
• Temperatura do ar
• Pressão
• Velocidade do vento
Exemplo: Curva diária do preço do barril do petróleo
Exemplo: A voz de um narrador ao ler as notícias de um
jornal produz um sinal acústico.
O microfone é um TRANSDUTOR, que converte este
sinal para a forma elétrica.
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Representações para sinais elétricos
v s (t ) = R s i s (t )
Figure 1.1 Two alternative representations of a signal source: (a) the Thévenin form, and (b) the Norton form.
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Sinal no domínio do tempo
Figure 1.2 An arbitrary voltage signal vs(t).
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Sinal Senoidal
v a (t ) = Va sen( wt )
w = 2πf rd/s
Freqüência angular
1
f = Hz
T
Freqüência
Figure 1.3 Sine-wave voltage signal of amplitude Va and frequency f = 1/T Hz. The angular frequency v = 2pf rad/s.
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Sinal de onda quadrada
Série de Fourier:
v(t ) =
4V
1
1
1
(sin w0 t + sin 3w0t + sin 5w0t + sin 7 w0t K)
π
3
5
7
Figure 1.4 A symmetrical square-wave signal of amplitude V.
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Representação gráfica do espectro de um sinal de onda quadrada
Espectro de frequências
Figure 1.5 The frequency spectrum (also known as the line spectrum) of the periodic square wave of Fig. 1.4.
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Espectro de freqüências de um sinal não periódico
Sinais de áudio:
espectro de freqüências compreendido
entre 20 Hz e 20KHz.
Sinal de vídeo analógico:
espectro de freqüências compreendido
entre 0 Hz e 4,5 MHz.
Figure 1.6 The frequency spectrum of an arbitrary waveform such as that in Fig. 1.2.
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Sinais Analógicos x Sinais Digitais
Sinal contínuo no tempo ou sinal analógico
Eletrônica analógica
Sinal discreto no tempo
Eletrônica digital
Figure 1.7 Sampling the continuous-time analog signal in (a) results in the discrete-time signal in (b).
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Sinal Digital Binário
Números representados na base 2
Figure 1.8 Variation of a particular binary digital signal with time.
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Conversor Analógico Digital
D = b0 2 0 + b1 21 + b2 2 2 + K + b N −1 2 N −1
Figure 1.9 Block-diagram representation of the analog-to-digital converter (ADC).
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Amplificadores de Sinais
Os transdutores muitas vezes fornecem sinais na faixa de alguns
micro-volts ou mili-volts.
Se:
vo (t ) = Avi (t )
O amplificador é linear.
A – ganho do amplificador
Caso contrário dizemos que o amplificador introduz DISTORÇÃO.
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Amplificadores de sinais
Terra do circuito
Figure 1.10 (a) Circuit symbol for amplifier. (b) An amplifier with a common terminal (ground) between the input and output
ports.
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Amplificador de Tensão
Característica de transferência
v
Ganho de tensão: Av = O
vI
Figure 1.11 (a) A voltage amplifier fed with a signal vI(t) and connected to a load resistance RL. (b) Transfer characteristic of a
linear voltage amplifier with voltage gain Av.
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Ganho de Potência e Ganho de Corrente
ganho de corrente:
i
Ai = O
iI
ganho de potência:
v i
A p = O O = Av Ai
vI iI
Ganhos em Decibéis
Ai ( db ) = 20 log | Ai |
Av ( db ) = 20 log | Av |
A p ( db ) = 10 log | A p |
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Fontes de Alimentação do amplificador
Pdc = V1 I1 + V2 I 2
Pdc + PI = PL + Pdissipada
PL
η=
× 100%
Pdc
Figure 1.12 An amplifier that requires two dc supplies (shown as batteries) for operation.
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Saturação do Amplificador
Para não ocorrer distorção:
L−
L+
≤ vI ≤
Av
Av
Figure 1.13 An amplifier transfer characteristic that is linear except for output saturation.
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Característica de Transferência não linear e polarização
Figure 1.14 (a) An amplifier transfer characteristic that shows considerable nonlinearity. (b) To obtain linear operation the
amplifier is biased as shown, and the signal amplitude is kept small. Observe that this amplifier is operated from a single power
supply, VDD.
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Exemplo 1.2
Um amplificador transistorizado tem a seguinte característica de transferência:
vO = 10 − 10 −11 e 40v I para v I ≥ 0 e vO ≥ 0.3V
Determine L- e L+ e os respectivos valores de vI.
Determine a tensão de polarização VI que resulta em VO = 5V e o ganho de tensão
no ponto de operação.
Figure 1.15 A sketch of the transfer characteristic of the amplifier of Example 1.2. Note that this amplifier is inverting (i.e., with
a gain that is negative).
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Convenção de símbolos
Valor instantâneo total
Amplitude
Componente C.C.
Figure 1.16 Symbol convention employed throughout the book.
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Amplificadores de Tensão
vo
=
vi
vo
=
vi
vo
=
vs
Figure 1.17 (a) Circuit model for the voltage amplifier. (b) The voltage amplifier with input signal source and load.
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Amplificadores em Cascata
Calcular:
Av, Ai e Ap. Expressar estes valores em decibéis
Figure 1.18 Three-stage amplifier for Example 1.3.
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Os quatro tipos de amplificadores
Amplificador de tensão
Amplificador de transcondutância
Amplificador de corrente
Amplificador de transresistência
Table 1.1 The Four Amplifier Types
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O transistor bipolar
RS = 5 KΩ rπ = 2,5 KΩ g m = 40mA / V
ro = 100 KΩ R L = 5KΩ
vo
=?
vs
Figure 1.19 (a) Small-signal circuit model for a bipolar junction transistor (BJT). (b) The BJT connected as an amplifier with the
emitter as a common terminal between input and output (called a common-emitter amplifier). (c) An alternative small-signal
circuit model for the BJT.
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Exercício 1.20
Determine a resistência de entrada do amplificador, Rin.
Figure E1.20
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O inversor lógico
Figure 1.28 A logic inverter operating from a dc supply VDD.
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Característica de transferência de tensão
Definições:
VIL – Máxima tensão de entrada que será interpretada
como nível lógico 0.
VIH – Mínima tensão de entrada que será interpretada
como nível lógico 1.
NMH = VOH – VIH – Margem de ruído em nível alto.
NML = VIL – VOL – Margem de ruído em nível baixo.
Figure 1.29 Voltage transfer characteristic of an inverter. The VTC is approximated by three straightline segments. Note the
four parameters of the VTC (VOH, VOL, VIL, and VIH) and their use in determining the noise margins (NMH and NML).
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Característica de transferência de tensão ideal
V
NM H = NM L = LL
2
Figure 1.30 The VTC of an ideal inverter.
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Implementação de Inversores TTL
Figure 1.31 (a) The simplest implementation of a logic inverter using a voltage-controlled switch; (b) equivalent circuit when vI
is low; and (c) equivalent circuit when vI is high. Note that the switch is assumed to close when vI is high.
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Implementação de Inversores CMOS
Figure 1.32 A more elaborate implementation of the logic inverter utilizing two complementary switches. This is the basis of
the CMOS inverter studied in Section 4.10.
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Implementação de Inversores ECL
Figure 1.33 Another inverter implementation utilizing a double-throw switch to steer the constant current IEE to RC1 (when vI is
high) or RC2 (when vI is low). This is the basis of the emitter-coupled logic (ECL) studied in Chapters 7 and 11.
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Figure 1.34 Example 1.6: (a) The inverter circuit after the switch opens (i.e., for t ≥ 0+). (b) Waveforms of vI and vO. Observe
that the switch is assumed to operate instantaneously. vO rises exponentially, starting at VOL and heading toward VOH .
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Atrasos de propagação
Figure 1.35 Definitions of propagation delays and transition times of the logic inverter.
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Problema 1.6
Determine expressões para VO e RO.
Figure P1.6
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Problema 1.10
Divisores de Corrente
Determine expressões para as correntes I1 e I2.
Figure P1.10
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Problema 1.14
Figure P1.14
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Problema 1.15
Aplique repetidamente o teorema de Thévenin e determine o
circuito equivalente de Thévenin do nó 4 para terra.
Figure P1.15
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Problema 1.16
Determine as correntes no circuito e a tensão no nó comum usando dois
métodos:
1 – Chame de I1 e I2 as correntes nos resistores R1 e R2 respectivamente.
Escreva duas equações de malhas.
2 – Chame de V a tensão no nó comum. Escreva uma equação de nó.
Figure P1.16
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Figure P1.17
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Figure P1.18
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Figure P1.37
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Figure P1.58
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Figure P1.63
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Figure P1.65
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Figure P1.67
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Figure P1.68
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Figure P1.72
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Figure P1.77
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Figure P1.79
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