Signal Generators and Waveform-Shaping Circuits

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1 CHAPTER 18 Signal Generators and Waveform-Shaping Circuits

Figure 18.1 The basic structure of a sinusoidal oscillator. A positive-feedback loop is formed by an amplifier and a frequency-selective network.

2 Figure 18.1 The basic structure of a sinusoidal oscillator. A positive-feedback loop is formed by an amplifier and a frequency-selective network. In an actual oscillator circuit, no input signal will be present; here an input signal xs is employed to help explain the principle of operation.

4 Figure 18.3 (a) An oscillator formed by connecting a positive-gain amplifier in a feedback loop with a bandpass RLC circuit. (b) Breaking the feedback loop at the input of the op amp to determine A(s) Vo(s)/Vi(s) and β(s) Vr(s)/Vo(s), and hence the loop gain A(s)β(s).

5 Figure 18.4 (a) A popular limiter circuit. (b) Transfer characteristic of the limiter circuit; L and L+ are given by Eqs. (18.8) and (18.9), respectively. (c) When Rf is removed, the limiter turns into a comparator with the characteristic shown.

6 Figure 18.5 A Wien-bridge oscillator without amplitude stabilization.

7 Figure 18.6 A Wien-bridge oscillator with a limiter used for amplitude control.

8 Figure 18.7 A Wien-bridge oscillator with an alternative method for amplitude stabilization.

9 Figure 18.8 A phase-shift oscillator.

10 Figure 18.9 A practical phase-shift oscillator with a limiter for amplitude stabilization.

11 Figure (a) A quadrature-oscillator circuit. (b) Equivalent circuit at the input of op amp 2.

12 Figure Block diagram of the active-filter-tuned oscillator.

13 Figure A practical implementation of the active-filter-tuned oscillator.

14 Figure Two commonly used configurations of LC-tuned oscillators: (a) Colpitts and (b) Hartley.

Figure 18.14 (a) A Colpitts oscillator in which the emitter is grounded and the output is taken at the collector.

15 Figure (a) A Colpitts oscillator in which the emitter is grounded and the output is taken at the collector. (b) Equivalent circuit of the Colpitts oscillator of (a). To simplify the analysis, Cμ and rπ are neglected. We can consider Cπ to be part of C2, and we can include ro in R.

16 Figure Complete discrete-circuit implementation for a Colpitts oscillator.

17 Figure (a) The cross-coupled LC oscillator. (b) Signal equivalent circuit of the cross-coupled oscillator in (a).

Figure 18.17 A piezoelectric crystal. (a) Circuit symbol. (b) Equivalent circuit.

18 Figure A piezoelectric crystal. (a) Circuit symbol. (b) Equivalent circuit. (c) Crystal reactance versus frequency [note that, neglecting the small resistance r, Zcrystal = jx(ω)].

19 Figure A Pierce crystal oscillator utilizing a CMOS inverter as an amplifier.

20 Figure A positive-feedback loop capable of bistable operation.

Figure 18.20 A physical analogy for the operation of the bistable circuit.

21 Figure A physical analogy for the operation of the bistable circuit. The ball cannot remain at the top of the hill for any length of time (a state of unstable equilibrium or metastability); the inevitably present disturbance will cause the ball to fall to one side or the other, where it can remain indefinitely (the two stable states).

24 Figure (a) Block diagram representation and transfer characteristic for a comparator having a reference, or threshold, voltage VR. (b) Comparator characteristic with hysteresis.

25 Figure Illustrating the use of hysteresis in the comparator characteristic as a means of rejecting interference.

Figure 18.26 (a) Connecting a bistable multivibrator with inverting transfer characteristics in a feedback loop with an RC circuit results in a square-wave generator.

27 Figure (a) Connecting a bistable multivibrator with inverting transfer characteristics in a feedback loop with an RC circuit results in a square-wave generator. (b) The circuit obtained when the bistable multivibrator is implemented with the circuit of Fig (a). (c) Waveforms at various nodes of the circuit in (b). This circuit is called an astable multivibrator.

28 Figure A general scheme for generating triangular and square waveforms.

29 Figure (a) An op-amp monostable circuit. (b) Signal waveforms in the circuit of (a).

30 Figure A block diagram representation of the internal circuit of the 555 integrated-circuit timer.

31 Figure (a) The 555 timer connected to implement a monostable multivibrator. (b) Waveforms of the circuit in (a).

32 Figure (a) The 555 timer connected to implement an astable multivibrator. (b) Waveforms of the circuit in (a).

33 Figure Using a nonlinear (sinusoidal) transfer characteristic to shape a triangular waveform into a sinusoid.

34 Figure (a) A three-segment sine-wave shaper. (b) The input triangular waveform and the output approximately sinusoidal waveform.

35 Figure A differential pair with an emitter-degeneration resistance used to implement a triangular-wave to sine-wave converter. Operation of the circuit can be graphically described by Fig

36 Figure E18.25

37 Figure P18.7

38 Figure P18.10

39 Figure P18.15

40 Figure P18.16

41 Figure P18.20

42 Figure P18.24

43 Figure P18.25

44 Figure P18.26

45 Figure P18.27

46 Figure P18.28

47 Figure P18.34

48 Figure P18.41

49 Figure P18.43

50 Figure P18.49

51 Figure P18.51

52 Figure P18.52

21/10/58. M2-3 Signal Generators. Bill Hewlett and Dave Packard s 1 st product (1939) US patent No HP 200A s schematic

21/10/58. M2-3 Signal Generators. Bill Hewlett and Dave Packard s 1 st product (1939) US patent No HP 200A s schematic M2-3 Signal Generators Bill Hewlett and Dave Packard s 1 st product (1939) US patent No.2267782 1 HP 200A s schematic 2 1 The basic structure of a sinusoidal oscillator. A positive feedback loop is formed