Main Page/PHYS 3220/Digital Oscilloscope

Digital Storage Oscilloscope

In this experiment we use a clock pulse generator to produce rectangular pulses which are recorded and analyzed using a modern digital storage oscilloscope capable of performing a fast fourier transform (FFT) on a given signal. Then the behaviour of a simple RC (integrator) circuit fed by a square wave pulse is analyzed both in the steady-state and transient (turn-on) regimes. Finally the square-wave pulse is used to induce damped harmonic motion in an LC circuit.

Introduction

The behaviour of short time-varying signals can be investigated easily with a digital storage oscilloscope (DSO) that will allow you to trigger single events and to store them for any length of time. Periodic signals play an important role in many areas of physics. Periodic signals are conveniently analyzed in terms of harmonic (or frequency) content, either by means of a Fourier series or by a Fourier transform [1]. Typically, oscilloscopes display signals in the time domain. The DSO you are using here will allow you to process these signals so they can be displayed in the frequency domain by using an FFT signal processing module included in the DSO. For a finite wavetrain recorded at discrete time intervals two parameters impose practical limitations on acquiring knowledge about the frequency content of a pulse. The sampling rate Δt limits the maximum frequency that can be recorded (intuitively: a signal that changes sign at every t_j = j Δt has the highest frequency that can be represented on the discrete time axis). The length of the recorded signal T limits the frequency resolution Δf: the lowest frequency that can be recorded corresponds to a wave with a period that equals T.

Thus, the Fourier transform that would be available in an ideal measurement (continuous sampling and infinite length of measurement)