Digital oscilloscopes Oscilloscope types

1 digital oscilloscopes

1.1 digital storage oscilloscope
1.2 digital sampling oscilloscopes
1.3 handheld oscilloscopes
1.4 pc-based oscilloscopes
1.5 mixed-signal oscilloscopes

digital oscilloscopes

while analog devices make use of continually varying voltages, digital devices employ binary numbers correspond samples of voltage. in case of digital oscilloscopes, analog-to-digital converter (adc) used change measured voltages digital information. waveforms taken series of samples. samples stored, accumulating until enough taken in order describe waveform, reassembled display. digital technology allows information displayed brightness, clarity, , stability. there are, however, limitations performance of oscilloscope. highest frequency @ oscilloscope can operate determined analog bandwidth of front-end components of instrument , sampling rate.

digital oscilloscopes can classified 3 primary categories: digital storage oscilloscopes, digital phosphor oscilloscopes, , digital sampling oscilloscopes. newer variants include pc-based oscilloscopes (which attach pc data processing , display) , mixed-signal oscilloscopes (which employ other functions in addition voltage measurement).

digital storage oscilloscope


screen of digital oscilloscope hp uses cathode-ray tube display

the digital storage oscilloscope, or dso short, preferred type industrial applications. instead of storage-type cathode ray tubes, dsos use digital memory, can store data long required without degradation. digital storage oscilloscope allows complex processing of signal high-speed digital signal processing circuits.

the vertical input digitized analog digital converter create data set stored in memory of microprocessor. data set processed , sent display, in dsos cathode ray tube, more lcd flat panel. dsos color lcd displays common. data set can sent on lan or wan processing or archiving. screen image can directly recorded on paper means of attached printer or plotter, without need oscilloscope camera. oscilloscope s own signal analysis software can extract many useful time-domain features (e.g., rise time, pulse width, amplitude), frequency spectra, histograms , statistics, persistence maps, , large number of parameters meaningful engineers in specialized fields such telecommunications, disk drive analysis , power electronics.

digital storage makes possible type of oscilloscope, equivalent-time sample oscilloscope. instead of taking consecutive samples after trigger event, 1 sample taken. however, oscilloscope able vary timebase precisely time sample, building picture of signal on subsequent repeats of signal. requires either clock or repeating pattern provided. type of oscilloscope used high speed communication because allows high sample rate , low amplitude noise compared traditional real-time oscilloscopes.

digital oscilloscopes limited principally performance of analog input circuitry, duration of sample window, , resolution of sample rate. when not using equivalent-time sampling, sampling frequency should @ least nyquist rate, double frequency of highest-frequency component of observed signal, otherwise aliasing occurs.

advantages on analog oscilloscope are:

brighter , bigger display color distinguish multiple traces
equivalent time sampling , averaging across consecutive samples or scans lead higher resolution down µv
peak detection
easy pan , zoom across multiple stored traces allows beginners work without trigger

this needs fast reaction of display (some oscilloscopes have 1 ms delay)
the knobs have large , turn smoothly


also slow traces temperature variation across day can recorded
allows automation.

a disadvantage of digital oscilloscopes limited refresh rate of screen. on analog oscilloscope, user can intuitive sense of trigger rate looking @ steadiness of crt trace. digital oscilloscope, screen looks same signal rate exceeds screen s refresh rate. additionally, difficult spot glitches or other rare phenomena on black-and-white screens of standard digital oscilloscopes; slight persistence of crt phosphors on analog oscilloscopes makes glitches visible if many subsequent triggers overwrite them. both of these difficulties have been overcome digital phosphor oscilloscopes , store data @ high refresh rate , display variable intensity, simulate trace persistence of crt oscilloscope.

digital sampling oscilloscopes

digital sampling oscilloscopes operate on same principle analog sampling oscilloscopes and, analog counterparts, of great use when analyzing high-frequency signals; is, repetitive signals frequencies higher oscilloscope s sampling rate. measuring repetitive signals, type can have bandwidth , high-speed timing ten times greater real-time oscilloscope.

a real-time oscilloscope, called “single-shot” scope, captures entire waveform on each trigger event. requires scope capture large number of data points in 1 continuous record. sequential equivalent-time sampling oscilloscope, called “sampling scope,” measures input signal once per trigger. next time scope triggered, small delay added , sample taken. large number of trigger events must occur in order collect enough samples build picture of waveform. measurement bandwidth determined frequency response of sampler can extend beyond 90 ghz.

an alternative sequential equivalent-time sampling called random equivalent-time sampling. samples synchronised not trigger events scope s internal sampling clock. causes them occur @ apparently random times relative trigger event. scope measures time interval between trigger , each sample, , uses locate sample correctly on x-axis. process continues until enough samples have been collected build picture of waveform. advantage of technique on sequential equivalent-time sampling scope can collect data before trigger event after it, in similar way pre-trigger function of real-time digital storage scopes. random equivalent-time sampling can integrated standard dso without requiring special sampling hardware, has disadvantage of poorer timing precision sequential sampling method.

handheld oscilloscopes

handheld oscilloscopes (also called scopemeters) useful many test , field service applications. today, hand held oscilloscope digital sampling oscilloscope, using liquid crystal display. typically, hand held oscilloscope has 2 analog input channels, 4 input channel versions available. instruments combine functions of digital multimeter oscilloscope. these lightweight , have accuracy.

pc-based oscilloscopes

a pc-based oscilloscope new type of oscilloscope emerging consists of specialized signal acquisition board (which can external usb or parallel port device, or internal add-on pci or isa card). hardware consists of electrical interface providing isolation , automatic gain controls, several high-speed analog-to-digital converters , buffer memory, or on-board digital signal processor (dsps). depending on exact hardware configuration, hardware best described digitizer, data logger or part of specialized automatic control system.

the pc provides display, control interface, disc storage, networking , electrical power acquisition hardware. viability of pc-based oscilloscopes depends on current widespread use , low cost of standardized pcs. since prices can range little us$100 as us$10,500 depending on capabilities, such instruments particularly suitable educational market, pcs commonplace equipment budgets low.

pco acquisition hardware, in cases, may consist of standard sound card or game port, if audio , low-frequency signals involved, though in many cases considerably more robust. pco can transfer data computer in 2 main ways — streaming, , block mode. in streaming mode data transferred pc in continuous flow without loss of data. way in pco connected pc (e.g., ieee1394, ethernet, usb etc.) dictate maximum achievable speed , thereby frequency , resolution using method. block mode utilizes on-board memory of pco collect block of data transferred pc after block has been recorded. pco hardware resets , records block of data. process happens quickly, time taken vary according size of block of data , speed @ can transferred. method enables higher sampling speed, in many cases hardware not record data whilst transferring existing block, meaning data loss occur.

the advantages of pc-based oscilloscopes include:

lower cost stand-alone oscilloscope, assuming user owns pc. professional-grade pco hardware (with bandwidth in mhz rather in khz range) tends more expensive typical pci sound card, , can cost more new pc (pco-chart).
easy exporting of data standard pc software such spreadsheets , word processors. or power tools numerical analysis software , tailored software.
ability control instrument running custom program on pc , thereby automate tests etc. or simple control setup remote location.
use of pc s networking , disc storage functions, cost lot when added self-contained oscilloscope.
pcs typically have large high-resolution color displays can easier read smaller displays found on conventional oscilloscopes. color can utilized differentiate waveforms. can show increased information including more of waveform or extras automatic waveform measurements , simultaneous alternative views.
portability when used laptop pc.
some smaller physically handheld oscilloscopes.

there disadvantages, include:

power-supply , electromagnetic noise pc circuits, requires careful , extensive shielding obtain low-level signal resolution.
data transfer rates pc, dependent upon connection method. affects maximum sampling rate , resolution achievable pco when streaming.
need owner install oscilloscope software on pc, may not compatible current release of pc operating system.
time pc boot, compared instant start-up of self-contained oscilloscope (although, modern oscilloscopes pcs or similar machines in disguise, distinction narrowing).

as more processing power , data storage included in oscilloscopes, distinction becoming blurred. mainstream oscilloscope vendors manufacture large-screen, pc-based oscilloscopes, fast (multi-ghz) input digitizers , highly customized user interfaces.

software pc may use sound card or game port acquire analog signals, instead of dedicated signal acquisition hardware. however, these devices have restricted input voltage ranges, limited precision/resolution, , restricted frequency ranges. ground reference these inputs same ground pc logic , power supply; may inject unacceptable amounts of noise circuit under test. however, these devices can useful demonstration, hobby use, or specific setups these factors won t interfere. ground reference can eliminated capacitor ac coupling or signal transformer.

if sound card used, frequency response limited audio range, , dc signals cannot measured without hardware modification. number of inputs limited number of recording channels , inputs can handle audio line-level voltages (usually ~1 vpp) without risk of damage.

if game port used acquisition hardware, possible sampling frequency low, typically below 1 khz, , input voltages can vary on range of couple of volts. in addition, game port cannot programmed specific sampling rate, nor can assigned precise quantization step. analog digital conversion accomplished triggering discharge of capacitor , measuring how long takes charge fixed threshold seen 0 1 transition on pc isa bus. means huge resistance @ input takes longer measure low resistance, results in asymmetrical sampling intervals. these limitations make suitable low-precision visualization of low frequency signals.

mixed-signal oscilloscopes

a mixed-signal oscilloscope (or mso) has 2 kinds of inputs, small number (typically 2 or four) of analog channels, , larger number (typically sixteen) of digital channels. these measurements acquired single time base, viewed on single display, , combination of these signals can used trigger oscilloscope.

an mso combines measurement capabilities , use model of digital storage oscilloscope (dso) of measurement capabilities of logic analyzer. msos typically lack advanced digital measurement capabilities , large number of digital acquisition channels of full-fledged logic analyzers, less complex use. typical mixed-signal measurement uses include characterization , debugging of hybrid analog/digital circuits like: embedded systems, analog-to-digital converters (adcs), digital-to-analog converters (dacs), , control systems.