An oscilloscope enables the visual display of a voltage that varies with time. One of the two input points is generally connected to the chassis and grounded, but this is not always the case.
A probe, attached to the input port of the oscilloscope, is connected to the voltage source. Some oscilloscopes have two or more input ports. Oscilloscopes with multiple ports can enable simultaneous viewing of waveforms, say, at the input and output of a circuit, for comparison and measurement, etc.
Analog and Digital Oscilloscopes
The analog oscilloscope uses a Cathode Ray Tube, and is also called a Cathode Ray Oscilloscope. In an analog oscilloscope, a thermally heated electron gun emits electrons, and an applied DC voltage causes the electron beam to impinge upon a fluorescent screen as a bright spot. A control grid results in axial movement of the electron beam and controls the number and speed of electrons in the beam. The momentum of electrons impinging on the screen decides the brightness of the spot. Applying a more negative voltage causes fewer electrons to impinge and is used for intensity control. A variable positive voltage on the second anode adjusts the trace sharpness. On applying an input voltage, the electron beam deflects proportionately, creating an instantaneous trace on the screen.
If a voltage input is applied to the vertical deflection plates and the horizontal deflection plates are grounded, the spot on the screen moves only up and down. On interchanging the signal to vertical and horizontal plates, the spot moves from left to right. If two signals of same frequency and in synchronization are applied to the two pairs of deflection plates, a trace results. The bright spot must repeat the same trace at least 30 times a second for the human eye to see it as a continuous trace.
By contrast, a digital oscilloscope first samples the waveform, and converts it into a digitally coded signal by an analog-to-digital converter. The oscilloscope processes this digital signal to reconstruct the waveform on the screen. Storage in a digital format enables data processing even by connected PC’s. In this oscilloscope, stored data including transients can be visualized or processed at any time, a feature not available in analogue oscilloscopes.
Displaying a Waveform
Whereas in analog oscilloscopes, continually varying voltages are used, in digital oscilloscopes, binary numbers are employed and these correspond to the input voltage samples. An ADC or analog to digital converter changes the measured voltage into its digital information. A series of samples of the waveform are taken and stored, until there is enough to describe a waveform. The information is then reassembled to be shown on the Liquid Crystal Display.
Unlike an analog oscilloscope, which uses a time-base and a linear saw-tooth waveform to display the waveforms repeatedly on the screen, a digital oscilloscope uses a very high stability clock to collect the information from the waveform.
Types of Digital Oscilloscopes
There are three types of digital oscilloscopes and they are classified as digital sampling oscilloscopes, digital phosphor oscilloscopes and the digital storage oscilloscopes.
Oscilloscopes, both analogue and digital, are among invaluable measuring and diagnostic tools in the electronics industry with newer applications continuously evolving with innovations in technology.