Lab 4 Variable duty cycle oscillator

Lab 4 Variable duty cycle oscillator - Lab 4 Variable Duty...

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Lab 4: Variable Duty Cycle Oscillator Design Objectives 1) Learn the use of oscillator circuits in both analog and digital systems 2) Understand the operation of an astable circuit 3) Understand hysteresis effect 4) Design a relaxation based nonlinear oscillator 5) Build and explore the operation of a variable duty cycle oscillator using a Schmitt trigger 6) Understand the fundamental characteristics of a pulse width modulator Background Sinusoidal, square, triangular, or pulse waveforms are frequently used in electronic systems. For example, in computer and control systems, clock pulses are used for timing, i.e ., to control data flow and the correct order of the operations. In communications such as radio and TV transmitters, sinusoidal waveforms are used to carry information. Finally, waveform generators are frequently used in test and measurement systems. We will utilize the hysteresis effect to produce square waves. Hysteresis is a memory effect since the current state of the system is determined by the prior state. Schmitt trigger, shown in the figure below, is an example of a system that shows hysteresis effect. Amount of voltage required to change the state (threshold voltages) are determined by the resistors R 1 and R 2 . Using superposition theory, the voltage at the positive (noninverting) input of the amplifier V + is given by When this voltage is equal to the reference voltage, the output changes its state. Note that this voltage is a function of the output voltage. Thus, the required input voltage to change the state is different for high-to-low and low-to-high transitions. We will design a nonlinear oscillator, referred to as a relaxation oscillator, by connecting an RC network to the negative (inverting) input of the amplifier, as shown in the figure below.

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A relaxation oscillator is an astable multivibrator that uses a Schmitt trigger and an RC time constant circuit. Note that the capacitor voltage determines the reference voltage. When the output is low, the capacitor discharges until the capacitor voltage is equal to V + which is set by the resistors and the output voltage. At this point, the output changes to high voltage. A new voltage is set at V
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Lab 4 Variable duty cycle oscillator - Lab 4 Variable Duty...

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