Digital oscilloscopes are sometimes called digital sampling oscilloscopes (DSO) or digital storage oscilloscope (DSO). Digital oscilloscopes operate by sampling a time varying analog signal periodically and storing the sample values in correlation with time in a waveform memory. These data may be then read out as locations in the memory are sequentially addressed by a clock signal to provide digital data which can be converted by a digital-to-analog converter to a time varying output signal which can be displayed on the face of a screen. Digital oscilloscopes chop input signals into discrete time points determined by an internal clock, quantize the instantaneous amplitude values at those points, and store the resulting digital representations in a digital memory. The display is regenerated from memory at a predetermined clock rate, and is manifested either as a series of dots, or connected dots. Because they store a stream of digitized data into a memory, digital oscilloscopes have powerful features concerning how they may be triggered. Digital oscilloscopes offer several advantages over analog oscilloscopes, such as the ability to make automatic measurements on the digital data and the ability to store the digital data in memory for post processing viewing, generating a hard copy, uploading to a computer, or storing on a diskette. Unlike analog oscilloscopes that must be triggered before it commences a trace, the digital oscilloscopes can be instructed to display the waveforms preceding a trigger event (negative time). Another advantage often present in such digital 'scopes is the ability to examine the digitized data stored in memory and automatically measure selected parameters of interest, such as frequency, voltage excursions, and rise times. Digital oscilloscopes are capable to display the same captured data in different ways. The ability to do this arises from there being more captured data than is displayed at any one time on the screen. Digital oscilloscope instruments have the flexibility of providing a wide range of storage, display and processing options, including one-half and one-quarter screen displays and graphics and multiple step processing programs. Digital oscilloscope instruments are particularly well suited for displaying complex signal waveforms where measurements and calculations on selected portions of the waveforms must be performed to provide waveform and numerical output displays indicative of selected parameters of the waveforms.

A digital oscilloscope is a complex instrument composed of many electronic hardware modules and many software modules that cooperate together in capturing, processing, displaying and storing information that characterizes the signals of interest to an operator. Digital oscilloscopes generally use raster scan displays to present the activity of electrical signals to their users. A raster scan display consists of a two dimensional array of pixels, with each pixel location being uniquely defined by a row number and column number. The more complex and expensive alternative to a single bit display is a multi-bit display, which can provide variable intensity or color variations as a substitute indicator of brightness. Digital oscilloscopes fall into two general categories. Single shot oscilloscopes begin sampling an event in real time when a trigger condition is satisfied. The limitations on their sampling speed are determined by the speed of the analog-to-digital converter, and the length of time over which an event may be sampled is limited by the size of the acquisition memory that receives the output from the converter. Random interleave or equivalent time sampling oscilloscopes rely on sampling a recurring event at different points in the event repeatedly over time. A single composite representation of the event is then compiled from each of the samples. The memory of a digital oscilloscope is often large enough that regardless of the selected time scale there is more stored waveform data than can be displayed on the screen, and the user has been given the ability to specify how the display is to be oriented relative to the trigger event. Digital oscilloscopes acquire information about the behavior of a circuit node by periodically sampling the voltage present at the node. The oscilloscope probe tip is placed in contact with the node and the probe and front end of the oscilloscope precisely replicate the signal and present it to an analog-to-digital converter. The output of the analog-to-digital converter is a series of multi-bit digital words that are stored in an acquisition memory. In a digital oscilloscope, voltage amplitude values derived from the data contents of an acquisition memory location determine the vertical location (row number) of an illuminated pixel, while time values derived from the addresses of the acquisition memory determine the horizontal location (column number).

A digital oscilloscope has two modes of operation. In the acquisition mode, the oscilloscope acquires an analog input signal by sampling the input signal at predetermined times, quantizing the successive samples so as to generate a succession of digital words representative of the magnitudes of the respective samples, and writing the digital words into memory locations that are related to the respective sample times. The oscilloscope responds to a trigger pulse by initiating a sequence of operations associated with terminating the signal acquisition. In the display mode, the contents of the waveform memory are used to generate a display, with greater or lesser resolution in the time dimension, of the waveform of the signal during the interval over which the acquisition took place. The display interval may include the trigger point, but even if it does, the position of the trigger point has no necessary relationship to the position of the waveform displayed on the oscilloscope screen. The precision of a digital oscilloscope is often expressed in terms of its risetime. Risetime is defined as the amount of time required for a voltage signal to rise from ten percent to ninety percent of its final voltage amplitude. The risetime of an oscilloscope is the risetime of the highest frequency signal that the oscilloscope can acquire. The fastest risetime oscilloscopes are the most precise. Typical digital oscilloscopes use a single level-crossing trigger detection to issue valid trigger signals to start or stop waveform acquisition. More sophisticated oscilloscopes employ a limited form of pattern recognition or other information in which an input signal deviates from an expected pattern to qualify valid triggering events. Signal averaging is often used in oscilloscopes to reduce the effects of random noise on the input signal. This is done by acquiring the signal several times, averaging the acquired data, and displaying the average.