This is a subdivision of the Oscilloscope article, discussing the various types and models of oscilloscopes in greater detail.
Digital oscilloscopes While analog devices make use of continually varying voltages, digital devices employ binary numbers which correspond to samples of the voltage. In the case of digital oscilloscopes, an analog-to-digital converter (ADC) is used to change the measured voltages into digital information. Waveforms are taken as a series of samples. The samples are stored, accumulating until enough are taken in order to describe the waveform, which are then reassembled for display. Digital technology allows the information to be displayed with brightness, clarity, and stability. There are, however, limitations as with the performance of any oscilloscope. The highest frequency at which the oscilloscope can operate is determined by the analog bandwidth of the front-end components of the instrument and the sampling rate.
Digital oscilloscopes can be classified into two primary categories: digital storage oscilloscopes and digital sampling oscilloscopes."Oscilloscope Types""XYZs of Oscilloscopes Primer" Newer variants include PC-based oscilloscopes (which attach to a PC for data processing and display) and mixed-signal oscilloscopes (which employ other functions in addition to voltage measurement).
Digital storage oscilloscope
The digital storage oscilloscope, or DSO for short, is now the preferred type for most industrial applications. Instead of storage-type cathode ray tubes, DSOs use digital memory, which can store data as long as required without degradation. A digital storage oscilloscope also allows complex processing of the signal by high-speed digital signal processing circuits.
The vertical input is digitized by an analog-to-digital converter to create a data set that is stored in the memory of a microprocessor. The data set is processed and then sent to the display, which in early DSOs was a cathode ray tube, but today is an LCD flat panel. DSOs with color LCDs are common. The sampling data set can be stored to internal or removable storage or sent over a LAN or USB for processing or archiving. A screen image can also be saved to internal or removable storage, or sent to a built-in or externally connected printer, without the need for an oscilloscope camera. The oscilloscope's own signal analysis software can extract many useful time-domain features (e.g., rise time, pulse width, amplitude), frequency spectra, histograms and statistics, persistence maps, and a large number of parameters meaningful to engineers in specialized fields such as telecommunications, disk drive analysis and power electronics..
Digital oscilloscopes are limited principally by the performance of the analog input circuitry, the duration of the sample window, and resolution of the sample rate. When not using equivalent-time sampling, the sampling frequency should be higher than the Nyquist rate which is double the frequency of the highest-frequency component of the observed signal, otherwise aliasing occurs.
Advantages over the analog oscilloscope are: Brighter and bigger display with color to distinguish multiple traces Simple one-shot acquisitions into memory without the issues that come with storage-type CRTs Much more versatile triggers No hiding of noise in the phosphor gloom as it happens on analog oscilloscopes The input signal is not just converted into a line on the screen, it is available as sample data which can be stored or further processed (i.e. through measurements and analysis tools that come with the oscilloscope) Averaging across consecutive samples or scans as well as specific HiRes modes which work through oversampling can lead to higher vertical resolution Versatile measurement and analysis functions make it easy to gather all relevant signal properties Peak detection to find specific events at long timebase settings on digital oscilloscopes with small memory (less relevant as newer oscilloscopes now come with large memories that keep the sample rate sufficiently high even at very long timebase settings) Easy pan and zoom Remote control via USB, Ethernet or GPIB
A disadvantage of older digital oscilloscopes is the limited waveform update rate (trigger rate) compared to their analog predecessors, which can make it difficult to spot "glitches" or other rare phenomena with digital oscilloscopes, especially older ones that have no persistence mode. However, thanks to improvements in waveform processing, newer digital oscilloscopes can reach trigger rates in excess of 1 million updates/second, which is more than the roughly 600,000 triggers/sec the best analog oscilloscopes were able to do. Newer digital oscilloscopes also come with analog persistence modes, which replicate the afterglow of an analog oscilloscope's phosphor CRT.
Digital sampling oscilloscopes Digital sampling oscilloscopes operate on the same principle as analog sampling oscilloscopes and, like their analog counterparts, are of great use when analyzing high-frequency signals; that is, repetitive signals whose frequencies are higher than the oscilloscope's sampling rate. For measuring repetitive signals, this type once used to offer bandwidth and high-speed timing up to ten times greater than any real-time oscilloscope.
A real-time oscilloscope, which also used to be called a “single-shot” scope, captures an entire waveform on each trigger event. This requires the scope to capture a large number of data points in one continuous record. A sequential equivalent-time sampling oscilloscope, sometimes simply called a “sampling scope,” measures the input signal only once per trigger. The next time the scope is triggered, a small delay is added and another sample is taken. Thus a large number of trigger events must occur in order to collect enough samples to build a picture of the waveform. The measurement bandwidth is determined by the frequency response of the sampler which currently can extend beyond 90 GHz.
An alternative to sequential equivalent-time sampling is called random equivalent-time sampling. Samples are synchronised not with trigger events but with the scope's internal sampling clock. This causes them to occur at apparently random times relative to the trigger event. The scope measures the time interval between the trigger and each sample, and uses this to locate the sample correctly on the x-axis. This process continues until enough samples have been collected to build up a picture of the waveform. The advantage of this technique over sequential equivalent-time sampling is that the scope can collect data from before the trigger event as well as after it, in a similar way to the pre-trigger function of most real-time digital storage scopes. Random equivalent-time sampling can be integrated into a standard DSO without requiring special sampling hardware, but has the disadvantage of poorer timing precision than the sequential sampling method.[Sampling Oscilloscope Techniques, http://www.cbtricks.com/miscellaneous/tech_publications/scope/sampling.pdf], Tek Technique Primer 47W-7209, Tektronix Inc., 1989, accessed 25 September 2013
However, due to the progress in ADC technology which has led to real-time oscilloscopes with bandwidths over 100 GHz, the demand for digital sampling oscilloscopes has been shrinking, as has the need for integrating equivalent time sampling in real-time oscilloscopes.
Handheld oscilloscopes Handheld oscilloscopes are useful for many test and field service applications. Today, a hand-held oscilloscope is usually a real-time oscilloscope, using a monochrome or color LCD. Typically, a hand-held oscilloscope has one or two analog input channels, but four-input-channel versions are also available. Some instruments combine the functions of a digital multimeter with the oscilloscope. These usually are lightweight and have good accuracy.
PC-based oscilloscopes
A PC-based oscilloscope is a type of digital oscilloscope which relies on a standard PC platform for waveform display and instrument control. In general, there are two types of PC-based oscilloscopes Standalone oscilloscopes which contain an internal PC platform (PC mainboard) – common with upper mid-range and high-end oscilloscopes External oscilloscopes which connect via USB or Ethernet to a separate PC (desktop or laptop)
At the end of the 1990s, Nicolet and HP introduced the first standalone PC-based oscilloscopes, where the "oscilloscope" part consisted of a specialized signal acquisition system, consisting of an electrical interface providing isolation and automatic gain controls, high-speed analog-to-digital converters, sample memory and on-board Digital Signal Processor (DSPs). The PC part ran Microsoft Windows as the operating system with an oscilloscope application on top, which displayed the waveform data and was used to control the instrument.
Since then, the high-end lines of standalone oscilloscopes of all four major oscilloscope manufacturers (HP/Agilent/Keysight, LeCroy, Tektronix, Rohde & Schwarz) have been based on a PC platform.
The other group of PC-based oscilloscopes are the external oscilloscopes, i.e. where the acquisition system is physically separate from the PC platform. Depending on the exact hardware configuration of the external oscilloscope, the hardware also could be described as a digitizer, a data logger or as a part of a specialized automatic control system. The separate PC provides the display, control interface, disc storage, networking and often the electrical power for the acquisition hardware. The external oscilloscope can transfer data to the computer in two main ways – streaming and block mode. In streaming mode the data is transferred to the PC in a continuous flow without any loss of data. The way in which the PCO is connected to the PC (e.g. Ethernet, USB etc.) will dictate the maximum achievable speed and thereby frequency and resolution using this method. Block mode utilizes the on-board memory of the external oscilloscope to collect a block of data which is then transferred to the PC after the block has been recorded. The acquisition hardware then resets and records another block of data. This process happens very quickly, but the time taken will vary according to the size of the block of data and the speed at which it can be transferred. This method enables a much higher sampling speed, but in many cases the hardware will not record data whilst it is transferring the existing block.
The advantages of a standalone PC-based oscilloscopes include: Easy exporting of data to standard PC software such as spreadsheets and word processors which can run on the oscilloscope Ability to run analysis tools like numerical analysis software and or signal analysis software directly on the oscilloscope Ability to run automation software to perform automatic tests Ability to easily control the oscilloscope from a remote location via networking
The advantages of external oscilloscopes are the same as for standalone PC-based oscilloscopes, plus in addition: Costs are often lower than for a comparable stand-alone oscilloscope, especially if the user already owns a suitable PC or laptop Standalone PCs and laptops typically have large high-resolution color displays which can be easier to read than the smaller displays found on conventional oscilloscopes. Portability when used with a laptop PC Some external oscilloscopes are much smaller physically than even handheld oscilloscopes
However, PC-based oscilloscopes, standalone or external, also have some disadvantages, which include: Power-supply and electromagnetic noise from PC circuits, which requires careful and extensive shielding to obtain good low-level signal resolution For external oscilloscopes, the need for the owner to install oscilloscope software on the PC, which may not be compatible with the current release of the PC operating system