Chapter 12 Signal generators and waveform-shaping circuits.ppt

Chapter 12 Signal generators and waveform-shaping circuits Introduction The basic structure of sinusoidaloscillators Basic Principles of Sinusoidal Oscillator The oscillator feedback loop The basic structure of a sinusoidal oscillator. A positive-feedback loop is formed by an amplifier and a frequency-selective network. Basic Principles of Sinusoidal Oscillator Feedback signal xf is summed with a positive sign The gain-with-feedback is The oscillation criterion: Barkhausen criterion. Basic Principles of Sinusoidal Oscillator Nonlinear amplitude control To ensure that oscillations will start, the Aβ is slightly greater than unity. As the power supply is turned on, oscillation will grown in amplitude. When the amplitude reaches the desired level, the nonlinear network comes into action and cause the Aβ to exactly unity. The implementation of the nonlinear amplitude-stabilization mechanism The first approach makes use of a limiter circuit The other mechanism for amplitude control utilizes an element whose resistance can be controlled by the amplitude of the output sinusoid. A Popular Limiter Circuit for Amplitude Control A Popular Limiter Circuit for Amplitude Control A Popular Limiter Circuit for Amplitude Control Oscillator Circuits Op Amp-RC Oscillator Circuits The Wien-Bridge Oscillator The phase-Shift Oscillator LC-Tuned Oscillator Colpitts oscillator Hareley oscillator Crystal Oscillator The Wien-Bridge Oscillator Analysis of frequency-selectivenetwork for Wien-bridge oscillator The Wien-Bridge Oscillator The loop gain transfer function Oscillating frequency To obtain sustained oscillation The Wien-Bridge Oscillator The Phase-Shift Oscillator The circuit consists of a negative-gain amplifier and three-section RC ladder network. Oscillating frequency is the one that the phase shift of the RC network is 1800 The Phase-Shift Oscillator The LC-Tuned oscillator The LC-Tuned oscillator Crystal Oscillators Crystal Oscillators Homewor