oscilloscope this article is about current oscilloscopes providing general information for history of oscilloscopes see oscilloscope history for detailed information about various types of oscilloscopes see oscilloscope types for the film distributor see oscilloscope laboratories oscilloscope cathoderay tube the interior of a cathoderay tube for use in an oscilloscope 1 deflection voltage electrode 2 electron gun 3 electron beam 4 focusing coil 5 phosphorcoated inner side of the screen a tektronix model 475a portable analog oscilloscope a typical instrument of the late 1970s a modern siglent shs800 handheld digital storage oscilloscope dso using an lcd for its display an oscilloscope displaying capacitor discharge an oscilloscope previously called an oscillograph and informally known as a scope or oscope cro for cathoderay oscilloscope or dso for the more modern digital storage oscilloscope is a type of electronic test instrument that allows observation of varying signal voltages usually as a twodimensional plot of one or more signals as a function of time other signals such as sound or vibration can be converted to voltages and displayed oscilloscopes are used to observe the change of an electrical signal over time such that voltage and time describe a shape which is continuously graphed against a calibrated scale the observed waveform can be analyzed for such properties as amplitude frequency rise time time interval distortion and others modern digital instruments may calculate and display these properties directly originally calculation of these values required manually measuring the waveform against the scales built into the screen of the instrument the oscilloscope can be adjusted so that repetitive signals can be observed as a continuous shape on the screen a storage oscilloscope allows single events to be captured by the instrument and displayed for a relatively long time allowing observation of events too fast to be directly perceptible oscilloscopes are used in the sciences medicine engineering automotive and the telecommunications industry generalpurpose instruments are used for maintenance of electronic equipment and laboratory work specialpurpose oscilloscopes may be used for such purposes as analyzing an automotive ignition system or to display the waveform of the heartbeat as an electrocardiogram early oscilloscopes used cathode ray tubes crts as their display element hence they were commonly referred to as cros and linear amplifiers for signal processing storage oscilloscopes used special storage crts to maintain a steady display of a single brief signal cros were later largely superseded by digital storage oscilloscopes dsos with thin panel displays fast analogtodigital converters and digital signal processors dsos without integrated displays sometimes known as digitisers are available at lower cost and use a generalpurpose digital computer to process and display waveforms features and uses basic oscilloscope description the basic oscilloscope as shown in the illustration is typically divided into four sections the display vertical controls horizontal controls and trigger controls the display is usually a crt historically or lcd panel which is laid out with both horizontal and vertical reference lines referred to as the graticule crt displays are additionally equipped with three controls focus intensity and beam finder the vertical section controls the amplitude of the displayed signal this section carries a voltsperdivision voltsdiv selector knob an acdcground selector switch and the vertical primary input for the instrument additionally this section is typically equipped with the vertical beam position knob the horizontal section controls the time base or sweep of the instrument the primary control is the secondsperdivision secdiv selector switch also included is a horizontal input for plotting dual xy axis signals the horizontal beam position knob is generally located in this section the trigger section controls the start event of the sweep the trigger can be set to automatically restart after each sweep or it can be configured to respond to an internal or external event the principal controls of this section will be the source and coupling selector switches an external trigger input ext input and level adjustment will also be included in addition to the basic instrument most oscilloscopes are supplied with a probe as shown the probe will connect to any input on the instrument and typically has a resistor of ten times the oscilloscopes input impedance this results in a 110x attenuation factor which helps to isolate the capacitive load presented by the probe cable from the signal being measured some probes have a switch allowing the operator to bypass the resistor when appropriate size and portability most modern oscilloscopes are lightweight portable instruments that are compact enough to be easily carried by a single person in addition to the portable units the market offers a number of miniature batterypowered instruments for field service applications laboratory grade oscilloscopes especially older units which use vacuum tubes are generally benchtop devices or may be mounted into dedicated carts specialpurpose oscilloscopes may be rackmounted or permanently mounted into a custom instrument housing inputs the signal to be measured is fed to one of the input connectors which is usually a coaxial connector such as a bnc or uhf type binding posts or banana plugs may be used for lower frequencies if the signal source has its own coaxial connector then a simple coaxial cable is used otherwise a specialized cable called a scope probe supplied with the oscilloscope is used in general for routine use an open wire test lead for connecting to the point being observed is not satisfactory and a probe is generally necessary generalpurpose oscilloscopes usually present an input impedance of 1 megohm in parallel with a small but known capacitance such as 20 picofarads scopes for use with very high frequencies may have 50ohm inputs which must be either connected directly to a 50ohm signal source or used with z0 or active probes lessfrequentlyused inputs include one or two for triggering the sweep horizontal deflection for xy mode displays and trace brighteningdarkening sometimes called zaxis inputs probes test probe oscilloscope probes open wire test leads flying leads are likely to pick up interference so they are not suitable for low level signals furthermore the leads have a high inductance so they are not suitable for high frequencies using a shielded cable iecoaxial cable is better for low level signals coaxial cable also has lower inductance but it has higher capacitance a typical 50ohm cable has about 90pf per meter consequently a onemeter direct 1x coaxial probe will load a circuit with a capacitance of about 110pf and a resistance of 1megohm to minimize loading attenuator probes eg10x probes are used a typical probe uses a 9megohm series resistor shunted by a lowvalue capacitor to make an rc compensated divider with the cable capacitance and scope input the rc time constants are adjusted to match for example the 9megohm series resistor is shunted by a 122pf capacitor for a time constant of 110microseconds the cable capacitance of 90pf in parallel with the scope input of 20pf and 1megohm total capacitance 110pf also gives a time constant of 110 microseconds in practice there will be an adjustment so the operator can precisely match the low frequency time constant called compensating the probe matching the time constants makes the attenuation independent of frequency at low frequencies where the resistance of r is much less than the reactance of c the circuit looks like a resistive divider at high frequencies resistance much greater than reactance the circuit looks like a capacitive divider the result is a frequency compensated probe for modest frequencies that presents a load of about 10megohms shunted by 12pf although such a probe is an improvement it does not work when the time scale shrinks to several cable transit times transit time is typically 5ns in that time frame the cable looks like its characteristic impedance and there will be reflections from the transmission line mismatch at the scope input and the probe that causes ringing probes with 101 attenuation are by far the most common for large signals and slightlyless capacitive loading 1001 probes may be used there are also probes that contain switches to select 101 or direct 11 ratios but this setting has significant capacitance tens of pf at the probe tip because the whole cables capacitance is now directly connected most oscilloscopes allow for probe attenuation factors displaying the effective sensitivity at the probe tip historically some autosensing circuitry used indicator lamps behind translucent windows in the panel to illuminate different parts of the sensitivity scale to do so the probe connectors modified bncs had an extra contact to define the probes attenuation a certain value of resistor connected to ground encodes the attenuation because probes wear out and because the autosensing circuitry is not compatible between different makes of oscilloscope autosensing probe scaling is not fool proof likewise manually setting the probe attenuation is prone to user error and it is a common mistake to have the probe scaling set incorrectly the resultant reading will then be wrong by a factor of 10 there are special high voltage probes which also form compensated attenuators with the oscilloscope input the probe body is physically large and some require partly filling a canister surrounding the series resistor with volatile liquid fluorocarbon to displace air at the oscilloscope end is a box with several waveformtrimming adjustments for safety a barrier disc keeps ones fingers distant from the point being examined maximum voltage is in the low tens of kv observing a high voltage ramp can create a staircase waveform with steps at different points every repetition until the probe tip is in contact until then a tiny arc charges the probe tip and its capacitance holds the voltage open circuit as the voltage continues to climb another tiny arc charges the tip further there are also current probes with cores that surround the conductor carrying current to be examined one type has a hole for the conductor and requires that the wire be passed through the hole they are for semipermanent or permanent mounting however other types for testing have a twopart core that permit them to be placed around a wire inside the probe a coil wound around the core provides a current into an appropriate load and the voltage across that load is proportional to current however this type of probe can sense ac only a moresophisticated probe includes a magnetic flux sensor hall effect sensor in the magnetic circuit the probe connects to an amplifier which feeds low frequency current into the coil to cancel the sensed field the magnitude of that current provides the lowfrequency part of the current waveform right down to dc the coil still picks up high frequencies there is a combining network akin to a loudspeaker crossover network front panel controls focus control this control adjusts crt focus to obtain the sharpest mostdetailed trace in practice focus needs to be adjusted slightly when observing quitedifferent signals which means that it needs to be an external control the control varies the voltage applied to a focusing anode within the crt flatpanel displays do not need focus adjustments and therefore do not include this control intensity control this adjusts trace brightness slow traces on crt oscilloscopes need less and fast ones especially if not often repeated require more brightness on flat panels however trace brightness is essentially independent of sweep speed because the internal signal processing effectively synthesizes the display from the digitized data astigmatism can also be called shape or spot shape adjusts the relative voltages on two of the crt anodes such that a displayed spot changes from elliptical in one plane through a circular spot to an ellipse at 90 degrees to the first this control may be absent from simpler oscilloscope designs or may even be an internal control it is not necessary with flat panel displays beam finder modern oscilloscopes have directcoupled deflection amplifiers which means the trace could be deflected offscreen they also might have their beam blanked without the operator knowing it to help in restoring a visible display the beam finder circuit overrides any blanking and limits the beam deflected to the visible portion of the screen beamfinder circuits often distort the trace while activated graticule the graticule is a grid of squares that serve as reference marks for measuring the displayed trace these markings whether located directly on the screen or on a removable plastic filter usually consist of a 1cm grid with closer tick marks often at 2mm on the centre vertical and horizontal axis one expects to see ten major divisions across the screen the number of vertical major divisions varies comparing the grid markings with the waveform permits one to measure both voltage vertical axis and time horizontal axis frequency can also be determined by measuring the waveform period and calculating its reciprocal on old and lowercost crt oscilloscopes the graticule is a sheet of plastic often with lightdiffusing markings and concealed lamps at the edge of the graticule the lamps had a brightness control highercost instruments have the graticule marked on the inside face of the crt to eliminate parallax errors better ones also had adjustable edge illumination with diffusing markings diffusing markings appear bright digital oscilloscopes however generate the graticule markings on the display in the same way as the trace external graticules also protect the glass face of the crt from accidental impact some crt oscilloscopes with internal graticules have an unmarked tinted sheet plastic light filter to enhance trace contrast this also serves to protect the faceplate of the crt accuracy and resolution of measurements using a graticule is relatively limited better instruments sometimes have movable bright markers on the trace that permit internal circuits to make more refined measurements both calibrated vertical sensitivity and calibrated horizontal time are set in 1 2 5 10 steps this leads however to some awkward interpretations of minor divisions digital oscilloscopes generate the graticule digitally which means that the scale can vary and accuracy of readings is much improved timebase controls computer model of the impact of increasing the timebase timedivision these select the horizontal speed of the crts spot as it creates the trace this process is commonly referred to as the sweep in all but the leastcostly modern oscilloscopes the sweep speed is selectable and calibrated in units of time per major graticule division quite a wide range of sweep speeds is generally provided from seconds to as fast as picoseconds in the fastest per division usually a continuouslyvariable control often a knob in front of the calibrated selector knob offers uncalibrated speeds typically slower than calibrated this control provides a range somewhat greater than that of consecutive calibrated steps making any speed available between the extremes holdoff control found on some better analog oscilloscopes this varies the time holdoff during which the sweep circuit ignores triggers it provides a stable display of some repetitive events in which some triggers would create confusing displays it is usually set to minimum because a longer time decreases the number of sweeps per second resulting in a dimmer trace see holdoff for a more detailed description vertical sensitivity coupling and polarity controls to accommodate a wide range of input amplitudes a switch selects calibrated sensitivity of the vertical deflection another control often in front of the calibratedselector knob offers a continuouslyvariable sensitivity over a limited range from calibrated to lesssensitive settings often the observed signal is offset by a steady component and only the changes are of interest a switch ac position connects a capacitor in series with the input that passes only the changes provided that they are not too slow slow would mean visible however when the signal has a fixed offset of interest or changes quite slowly the input is connected directly dc switch position most oscilloscopes offer the dc input option for convenience to see where zero volts input currently shows on the screen many oscilloscopes have a third switch position gnd that disconnects the input and grounds it often in this case the user centers the trace with the vertical position control better oscilloscopes have a polarity selector normally a positive input moves the trace upward but this permits invertingpositive deflects the trace downward horizontal sensitivity control this control is found only on more elaborate oscilloscopes it offers adjustable sensitivity for external horizontal inputs it is only active when the instrument is in xy mode that is when the internal horizontal sweep is not in use vertical position control computer model of vertical position y offset varying in a sine way the vertical position control moves the whole displayed trace up and down it is used to set the noinput trace exactly on the center line of the graticule but also permits offsetting vertically by a limited amount with direct coupling adjustment of this control can compensate for a limited dc component of an input horizontal position control computer model of horizontal position control from x offset increasing the horizontal position control moves the display sidewise it usually sets the left end of the trace at the left edge of the graticule but it can displace the whole trace when desired this control also moves the xy mode traces sidewise in some instruments and can compensate for a limited dc component as for vertical position dualtrace controls please see dual and multipletrace oscilloscopes below dualtrace controls green trace y 30sin01t05 teal trace y 30sin03t each input channel usually has its own set of sensitivity coupling and position controls although some fourtrace oscilloscopes have only minimal controls for their third and fourth channels dualtrace oscilloscopes have a mode switch to select either channel alone both channels or in some an xy display which uses the second channel for x deflection when both channels are displayed the type of channel switching can be selected on some oscilloscopes on others the type depends upon timebase setting if manually selectable channel switching can be freerunning asynchronous or between consecutive sweeps some philips dualtrace analog oscilloscopes had a fast analog multiplier and provided a display of the product of the input channels multipletrace oscilloscopes have a switch for each channel to enable or disable display of that traces signal delayedsweep controls please see delayed sweep below these include controls for the delayedsweep timebase which is calibrated and often also variable the slowest speed is several steps faster than the slowest main sweep speed although the fastest is generally the same a calibrated multiturn delay time control offers wide range high resolution delay settings it spans the full duration of the main sweep and its reading corresponds to graticule divisions but with much finer precision its accuracy is also superior to that of the display a switch selects display modes main sweep only with a brightened region showing when the delayed sweep is advancing delayed sweep only or on some a combination mode good crt oscilloscopes include a delayedsweep intensity control to allow for the dimmer trace of a muchfaster delayed sweep that nevertheless occurs only once per main sweep such oscilloscopes also are likely to have a trace separation control for multiplexed display of both the main and delayed sweeps together sweep trigger controls please see triggered sweep below a switch selects the trigger source it can be an external input one of the vertical channels of a dual or multipletrace oscilloscope or the ac line mains frequency another switch enables or disables auto trigger mode or selects single sweep if provided in the oscilloscope either a springreturn switch position or a pushbutton arms single sweeps a level control varies the voltage on the waveform which generates a trigger and the slope switch selects positivegoing or negativegoing polarity at the selected trigger level basic types of sweep triggered sweep type 465 tektronix oscilloscope this was a popular analog oscilloscope portable and is a representative example to display events with unchanging or slowly visibly changing waveforms but occurring at times that may not be evenly spaced modern oscilloscopes have triggered sweeps compared to simpler oscilloscopes with sweep oscillators that are always running triggeredsweep oscilloscopes are markedly more versatile a triggered sweep starts at a selected point on the signal providing a stable display in this way triggering allows the display of periodic signals such as sine waves and square waves as well as nonperiodic signals such as single pulses or pulses that do not recur at a fixed rate with triggered sweeps the scope will blank the beam and start to reset the sweep circuit each time the beam reaches the extreme right side of the screen for a period of time called holdoff extendable by a frontpanel control on some better oscilloscopes the sweep circuit resets completely and ignores triggers once holdoff expires the next trigger starts a sweep the trigger event is usually the input waveform reaching some userspecified threshold voltage trigger level in the specified direction going positive or going negativetrigger polarity in some cases variable holdoff time can be really useful to make the sweep ignore interfering triggers that occur before the events to be observed in the case of repetitive but complex waveforms variable holdoff can create a stable display that cannot otherwise be achieved holdoff trigger holdoff defines a certain period following a trigger during which the scope will not trigger again this makes it easier to establish a stable view of a waveform with multiple edges which would otherwise cause another trigger example imagine the following repeating waveform the green line is the waveform the red vertical partial line represents the location of the trigger and the yellow line represents the trigger level if the scope was simply set to trigger on every rising edge this waveform would cause three triggers for each cycle assuming the signal is fairly high frequency the scope would probably look something like this except that on the scope each trigger would be the same channel and so would be the same color it is desired to set the scope to only trigger on one edge per cycle so it is necessary to set the holdoff to be slightly less than the period of the waveform that will prevent it from triggering more than once per cycle but still allow it to trigger on the first edge of the next cycle automatic sweep mode triggered sweeps can display a blank screen if there are no triggers to avoid this these sweeps include a timing circuit that generates freerunning triggers so a trace is always visible once triggers arrive the timer stops providing pseudotriggers automatic sweep mode can be deselected when observing low repetition rates recurrent sweeps if the input signal is periodic the sweep repetition rate can be adjusted to display a few cycles of the waveform early tube oscilloscopes and lowestcost oscilloscopes have sweep oscillators that run continuously and are uncalibrated such oscilloscopes are very simple comparatively inexpensive and were useful in radio servicing and some tv servicing measuring voltage or time is possible but only with extra equipment and is quite inconvenient they are primarily qualitative instruments they have a few widely spaced frequency ranges and relatively widerange continuous frequency control within a given range in use the sweep frequency is set to slightly lower than some submultiple of the input frequency to display typically at least two cycles of the input signal so all details are visible a very simple control feeds an adjustable amount of the vertical signal or possibly a related external signal to the sweep oscillator the signal triggers beam blanking and a sweep retrace sooner than it would occur freerunning and the display becomes stable single sweeps some oscilloscopes offer thesethe sweep circuit is manually armed typically by a pushbutton or equivalent armed means its ready to respond to a trigger once the sweep is complete it resets and will not sweep until rearmed this mode combined with an oscilloscope camera captures singleshot events types of trigger include external trigger a pulse from an external source connected to a dedicated input on the scope edge trigger an edgedetector that generates a pulse when the input signal crosses a specified threshold voltage in a specified direction these are the mostcommon types of triggers the level control sets the threshold voltage and the slope control selects the direction negative or positivegoing the first sentence of the description also applies to the inputs to some digital logic circuits those inputs have fixed threshold and polarity response video trigger a circuit that extracts synchronizing pulses from video formats such as pal and ntsc and triggers the timebase on every line a specified line every field or every frame this circuit is typically found in a waveform monitor device although some better oscilloscopes include this function delayed trigger which waits a specified time after an edge trigger before starting the sweep as described under delayed sweeps a trigger delay circuit typically the main sweep extends this delay to a known and adjustable interval in this way the operator can examine a particular pulse in a long train of pulses some recent designs of oscilloscopes include more sophisticated triggering schemes these are described toward the end of this article delayed sweeps more sophisticated analog oscilloscopes contain a second timebase for a delayed sweep a delayed sweep provides a very detailed look at some small selected portion of the main timebase the main timebase serves as a controllable delay after which the delayed timebase starts this can start when the delay expires or can be triggered only after the delay expires ordinarily the delayed timebase is set for a faster sweep sometimes much faster such as 10001 at extreme ratios jitter in the delays on consecutive main sweeps degrades the display but delayedsweep triggers can overcome that the display shows the vertical signal in one of several modes the main timebase or the delayed timebase only or a combination thereof when the delayed sweep is active the main sweep trace brightens while the delayed sweep is advancing in one combination mode provided only on some oscilloscopes the trace changes from the main sweep to the delayed sweep once the delayed sweep starts although less of the delayed fast sweep is visible for longer delays another combination mode multiplexes alternates the main and delayed sweeps so that both appear at once a trace separation control displaces them dsos allow waveforms to be displayed in this way without offering a delayed timebase as such dual and multipletrace oscilloscopes oscilloscopes with two vertical inputs referred to as dualtrace oscilloscopes are extremely useful and commonplace using a singlebeam crt they multiplex the inputs usually switching between them fast enough to display two traces apparently at once less common are oscilloscopes with more traces four inputs are common among these but a few kikusui for one offered a display of the sweep trigger signal if desired some multitrace oscilloscopes use the external trigger input as an optional vertical input and some have third and fourth channels with only minimal controls in all cases the inputs when independently displayed are timemultiplexed but dualtrace oscilloscopes often can add their inputs to display a realtime analog sum inverting one channel provides a difference provided that neither channel is overloaded this difference mode can provide a moderateperformance differential input switching channels can be asynchronous that is freerunning with trace blanking while switching or after each horizontal sweep is complete asynchronous switching is usually designated chopped while sweepsynchronized is designated alt a given channel is alternately connected and disconnected leading to the term chopped multitrace oscilloscopes also switch channels either in chopped or alternate modes in general chopped mode is better for slower sweeps it is possible for the internal chopping rate to be a multiple of the sweep repetition rate creating blanks in the traces but in practice this is rarely a problem the gaps in one trace are overwritten by traces of the following sweep a few oscilloscopes had a modulated chopping rate to avoid this occasional problem alternate mode however is better for faster sweeps true dualbeam crt oscilloscopes did exist but were not common one type cossor uk had a beamsplitter plate in its crt and singleended deflection following the splitter others had two complete electron guns requiring tight control of axial rotational mechanical alignment in manufacturing the crt beamsplitter types had horizontal deflection common to both vertical channels but dualgun oscilloscopes could have separate time bases or use one time base for both channels multiplegun crts up to ten guns were made in past decades with ten guns the envelope bulb was cylindrical throughout its length also see crt invention in oscilloscope history the vertical amplifier in an analog oscilloscope the vertical amplifier acquires the signal to be displayed in better oscilloscopes it delays them by a fraction of a microsecond and provides a signal large enough to deflect the crts beam that deflection is at least somewhat beyond the edges of the graticule and more typically some distance offscreen the amplifier has to have low distortion to display its input accurately it must be linear and it has to recover quickly from overloads as well its timedomain response has to represent transients accuratelyminimal overshoot rounding and tilt of a flat pulse top a vertical input goes to a frequencycompensated step attenuator to reduce large signals to prevent overload the attenuator feeds a lowlevel stage or a few which in turn feed gain stages and a delayline driver if there is a delay following are more gain stages up to the final output stage which develops a large signal swing tens of volts sometimes over 100 volts for crt electrostatic deflection in dual and multipletrace oscilloscopes an internal electronic switch selects the relatively lowlevel output of one channels amplifiers and sends it to the following stages of the vertical amplifier which is only a single channel so to speak from that point on in freerunning chopped mode the oscillator which may be simply a different operating mode of the switch driver blanks the beam before switching and unblanks it only after the switching transients have settled part way through the amplifier is a feed to the sweep trigger circuits for internal triggering from the signal this feed would be from an individual channels amplifier in a dual or multitrace oscilloscope the channel depending upon the setting of the trigger source selector this feed precedes the delay if there is one which allows the sweep circuit to unblank the crt and start the forward sweep so the crt can show the triggering event highquality analog delays add a modest cost to an oscilloscope and are omitted in oscilloscopes that are costsensitive the delay itself comes from a special cable with a pair of conductors wound around a flexible magnetically soft core the coiling provides distributed inductance while a conductive layer close to the wires provides distributed capacitance the combination is a wideband transmission line with considerable delay per unit length both ends of the delay cable require matched impedances to avoid reflections xy mode a 24hour clock displayed on a crt oscilloscope configured in xy mode as a vector monitor with dual r2r dacs to generate the analog voltages most modern oscilloscopes have several inputs for voltages and thus can be used to plot one varying voltage versus another this is especially useful for graphing iv curves current versus voltage characteristics for components such as diodes as well lissajous patterns lissajous figures are an example of how an oscilloscope can be used to track phase differences between multiple input signals this is very frequently used in broadcast engineering to plot the left and right stereophonic channels to ensure that the stereo generator is calibrated properly historically stable lissajous figures were used to show that two sine waves had a relatively simple frequency relationship a numericallysmall ratio they also indicated phase difference between two sine waves of the same frequency the xy mode also allows the oscilloscope to be used as a vector monitor to display images or user interfaces many early games such as tennis for two used an oscilloscope as an output device complete loss of signal in an xy crt display means that the beam strikes a small spot which risks burning the phosphor older phosphors burned more easily some dedicated xy displays reduce beam current greatly or blank the display entirely if there are no inputs present bandwidth as with all practical instruments oscilloscopes do not respond equally to all possible input frequencies the range of frequencies an oscilloscope can usefully display is referred to as its bandwidth bandwidth applies primarily to the yaxis although the xaxis sweeps have to be fast enough to show the highestfrequency waveforms the bandwidth is defined as the frequency at which the sensitivity is 0707 of that at dc or the lowest ac frequency a drop of 3 db states that there is a noticeable effect on the accuracy of voltage measurements at only 20 percent of the stated bandwidth some oscilloscopes specifications do include a narrower tolerance range within the stated bandwidth probes also have bandwidth limits and must be chosen and used to properly handle the frequencies of interest to achieve the flattest response most probes must be compensated an adjustment performed using a test signal from the oscilloscope to allow for the reactance of the probes cable another related specification is rise time this is the duration of the fastest pulse that can be resolved by the scope it is related to the bandwidth approximately by bandwidth in hz x rise time in seconds 035 for example an oscilloscope intended to resolve pulses with a rise time of 1 nanosecond would have a bandwidth of 350mhz in analog instruments the bandwidth of the oscilloscope is limited by the vertical amplifiers and the crt or other display subsystem in digital instruments the sampling rate of the analog to digital converter adc is a factor but the stated analog bandwidth and therefore the overall bandwidth of the instrument is usually less than the adcs nyquist frequency this is due to limitations in the analog signal amplifier deliberate design of the antialiasing filter that precedes the adc or both for a digital oscilloscope a rule of thumb is that the continuous sampling rate should be ten times the highest frequency desired to resolve for example a 20megasamplesecond rate would be applicable for measuring signals up to about 2megahertz this allows the antialiasing filter to be designed with a 3db down point of 2mhz and an effective cutoff at 10mhz the nyquist frequency avoiding the artifacts of a very steep brickwall filter a sampling oscilloscope can display signals of considerably higher frequency than the sampling rate if the signals are exactly or nearly repetitive it does this by taking one sample from each successive repetition of the input waveform each sample being at an increased time interval from the trigger event the waveform is then displayed from these collected samples this mechanism is referred to as equivalenttime sampling some oscilloscopes can operate in either this mode or in the more traditional realtime mode at the operators choice other features a computer model of the sweep of the oscilloscopesome oscilloscopes have cursors which are lines that can be moved about the screen to measure the time interval between two points or the difference between two voltages a few older oscilloscopes simply brightened the trace at movable locations these cursors are more accurate than visual estimates referring to graticule lines better quality general purpose oscilloscopes include a calibration signal for setting up the compensation of test probes this is often a 1khz squarewave signal of a definite peaktopeak voltage available at a test terminal on the front panel some better oscilloscopes also have a squaredoff loop for checking and adjusting current probes sometimes the event that the user wants to see may only happen occasionally to catch these events some oscilloscopes known as storage scopes preserve the most recent sweep on the screen this was originally achieved by using a special crt a storage tube which would retain the image of even a very brief event for a long time some digital oscilloscopes can sweep at speeds as slow as once per hour emulating a strip chart recorder that is the signal scrolls across the screen from right to left most oscilloscopes with this facility switch from a sweep to a stripchart mode at about one sweep per ten seconds this is because otherwise the scope looks broken its collecting data but the dot cannot be seen in current oscilloscopes digital signal sampling is more often used for all but the simplest models samples feed fast analogtodigital converters following which all signal processing and storage is digital many oscilloscopes have different plugin modules for different purposes eghighsensitivity amplifiers of relatively narrow bandwidth differential amplifiers amplifiers with four or more channels sampling plugins for repetitive signals of very high frequency and specialpurpose plugins including audioultrasonic spectrum analyzers and stableoffsetvoltage directcoupled channels with relatively high gain examples of use lissajous figures on an oscilloscope with 90degrees phase difference between x and yinputs one of the most frequent uses of scopes is troubleshooting malfunctioning electronic equipment one of the advantages of a scope is that it can graphically show signals where a voltmeter may show a totally unexpected voltage a scope may reveal that the circuit is oscillating in other cases the precise shape or timing of a pulse is important in a piece of electronic equipment for example the connections between stages eg electronic mixers electronic oscillators amplifiers may be probed for the expected signal using the scope as a simple signal tracer if the expected signal is absent or incorrect some preceding stage of the electronics is not operating correctly since most failures occur because of a single faulty component each measurement can prove that half of the stages of a complex piece of equipment either work or probably did not cause the fault once the faulty stage is found further probing can usually tell a skilled technician exactly which component has failed once the component is replaced the unit can be restored to service or at least the next fault can be isolated this sort of troubleshooting is typical of radio and tvreceivers as well as audio amplifiers but can apply to quitedifferent devices such as electronic motor drives another use is to check newly designed circuitry very often a newly designed circuit will misbehave because of design errors bad voltage levels electrical noise etc digital electronics usually operate from a clock so a dualtrace scope which shows both the clock signal and a test signal dependent upon the clock is useful storage scopes are helpful for capturing rare electronic events that cause defective operation pictures of use heterodyne ac hum on sound sum of a lowfrequency and a highfrequency signal bad filter on sine dual trace showing different time bases on each trace automotive use first appearing in the 1970s for ignition system analysis automotive oscilloscopes are becoming an important workshop tool for testing sensors and output signals on electronic engine management systems braking and stability systems some oscilloscopes can trigger and decode serial bus messages such as the can bus commonly used in automotive applications selection for work at high frequencies and with fast digital signals the bandwidth of the vertical amplifiers and sampling rate must be high enough for generalpurpose use a bandwidth of at least 100mhz is usually satisfactory a much lower bandwidth is sufficient for audiofrequency applications only a useful sweep range is from one second to 100nanoseconds with appropriate triggering and for analog instruments sweep delay a welldesigned stable trigger circuit is required for a steady display the chief benefit of a quality oscilloscope is the quality of the trigger circuit key selection criteria of a dso apart from input bandwidth are the sample memory depth and sample rate early dsos in the mid to late 1990s only had a few kb of sample memory per channel this is adequate for basic waveform display but does not allow detailed examination of the waveform or inspection of long data packets for example even entrylevel 500 modern dsos now have 1mb or more of sample memory per channel and this has become the expected minimum in any modern dso any modern realtime sample rate dso will have typically 510 times the input bandwidth in sample rate so a 100mhz bandwidth dso would have 500mss 1gss sample rate the theoretical minimum sample rate required using sinxx interpolation is 25 times the bandwidth analog oscilloscopes have been almost totally displaced by digital storage scopes except for use exclusively at lower frequencies greatly increased sample rates have largely eliminated the display of incorrect signals known as aliasing that was sometimes present in the first generation of digital scopes the problem can still occur when for example viewing a short section of a repetitive waveform that repeats at intervals thousands of times longer than the section viewed for example a short synchronization pulse at the beginning of a particular television line with an oscilloscope that cannot store the extremely large number of samples between one instance of the short section and the next the used test equipment market particularly online auction venues typically has a wide selection of older analog scopes available however it is becoming more difficult to obtain replacement parts for these instruments and repair services are generally unavailable from the original manufacturer used instruments are usually out of calibration and recalibration by companies with the equipment and expertise usually costs more than the secondhand value of the instrument as of 2007 on the lowest end an inexpensive hobbygrade singlechannel dso could be purchased for under 90 as of june 2011 these often have limited bandwidth and other facilities but fulfill the basic functions of an oscilloscope software many oscilloscopes today provide one or more external interfaces to allow remote instrument control by external software these interfaces or buses include gpib ethernet serial port and usb types and models oscilloscope types the following section is a brief summary of various types and models available for a detailed discussion refer to the other article cathoderay oscilloscope cro further information oscilloscope types cathoderay oscilloscope example of an analog oscilloscope lissajous figure showing a harmonic relationship of 1 horizontal oscillation cycle to 3 vertical oscillation cycles for analog television an analog oscilloscope can be used as a vectorscope to analyze complex signal properties such as this display of smpte color bars the earliest and simplest type of oscilloscope consisted of a cathode ray tube a vertical amplifier a timebase a horizontal amplifier and a power supply these are now called analog scopes to distinguish them from the digital scopes that became common in the 1990s and 2000s analog scopes do not necessarily include a calibrated reference grid for size measurement of waves and they may not display waves in the traditional sense of a line segment sweeping from left to right instead they could be used for signal analysis by feeding a reference signal into one axis and the signal to measure into the other axis for an oscillating reference and measurement signal this results in a complex looping pattern referred to as a lissajous curve the shape of the curve can be interpreted to identify properties of the measurement signal in relation to the reference signal and is useful across a wide range of oscillation frequencies dualbeam oscilloscope the dualbeam analog oscilloscope can display two signals simultaneously a special dualbeam crt generates and deflects two separate beams although multitrace analog oscilloscopes can simulate a dualbeam display with chop and alternate sweeps those features do not provide simultaneous displays real time digital oscilloscopes offer the same benefits of a dualbeam oscilloscope but they do not require a dualbeam display the disadvantages of the dual trace oscilloscope are that it cannot switch quickly between the traces and it cannot capture two fast transient events in order to avoid this problems a dual beam oscilloscope is used analog storage oscilloscope further information cathode ray tube oscilloscope crts further information oscilloscope types analog storage oscilloscope trace storage is an extra feature available on some analog scopes they used directview storage crts storage allows the trace pattern that normally decays in a fraction of a second to remain on the screen for several minutes or longer an electrical circuit can then be deliberately activated to store and erase the trace on the screen digital oscilloscopes digital storage oscilloscope 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 analogtodigital converter adc is used to change the measured voltages into digital information a siglent sds1000 series oscilloscope a modern low cost dso the digital storage oscilloscope or dso for short is now the preferred type for most industrial applications although simple analog cros are still used by hobbyists it replaces the electrostatic storage method used in analog storage scopes with digital memory which can store data as long as required without degradation and with uniform brightness it also allows complex processing of the signal by highspeed digital signal processing circuits a standard dso is limited to capturing signals with a bandwidth of less than half the sampling rate of the adc called the nyquist limit there is a variation of the dso called the digital sampling oscilloscope that can exceed this limit for certain types of signal such as highspeed communications signals where the waveform consists of repeating pulses this type of dso deliberately samples at a much lower frequency than the nyquist limit and then uses signal processing to reconstruct a composite view of a typical pulse a similar technique with analog rather than digital samples was used before the digital era in analog sampling oscilloscopes a digital phosphor oscilloscope dpo uses color information to convey information about a signal it may for example display infrequent signal data in blue to make it stand out in a conventional analog scope such a rare trace may not be visible mixedsignal oscilloscopes a mixedsignal oscilloscope or mso has two kinds of inputs a small number of analog channels typically two or four and a larger number of digital channelstypically sixteen it provides the ability to accurately timecorrelate analog and digital channels thus offering a distinct advantage over a separate oscilloscope and logic analyser typically digital channels may be grouped and displayed as a bus with each bus value displayed at the bottom of the display in hex or binary on most msos the trigger can be set across both analog and digital channels mixeddomain oscilloscopes in a mixeddomain oscilloscope mdo you have an additional rf input port that goes into a spectrum analyzer part it links those traditionally separate instruments so that you can eg time correlate events in the time domain like a specific serial data package with events happening in the frequency domain like rf transmissions handheld oscilloscopes siglent handheld oscilloscope shs800 series further information oscilloscope types handheld oscilloscopes handheld oscilloscopes are useful for many test and field service applications today a hand held oscilloscope is usually a digital sampling oscilloscope using a liquid crystal display many handheld and bench oscilloscopes have the ground reference voltage common to all input channels if more than one measurement channel is used at the same time all the input signals must have the same voltage reference and the shared default reference is the earth if there is no differential preamplifier or external signal isolator this traditional desktop oscilloscope is not suitable for floating measurements occasionally an oscilloscope user will break the ground pin in the power supply cord of a benchtop oscilloscope in an attempt to isolate the signal common from the earth ground this practice is unreliable since the entire stray capacitance of the instrument cabinet will be connected into the circuit since it is also a hazard to break a safety ground connection instruction manuals strongly advise against this practice siglent isolation oscilloscope shs1000 series some models of oscilloscope have isolated inputs where the signal reference level terminals are not connected together each input channel can be used to make a floating measurement with an independent signal reference level measurements can be made without tying one side of the oscilloscope input to the circuit signal common or ground reference the isolation available is categorized as shown below overvoltage category operating voltage effective value of acdc to ground peak instantaneous voltage repeated 20 times test resistor cat i 600v 2500v 30 cat i 1000v 4000v 30 cat ii 600v 4000v 12 cat ii 1000v 6000v 12 cat iii 600v 6000v 2 pcbased oscilloscopes picoscope 6000 digital pcbased oscilloscope using a laptop computer for display processing further information oscilloscope types pcbased oscilloscopes a new type of oscilloscope is emerging that consists of a specialized signal acquisition board which can be an external usb or parallel port device or an internal addon pci or isa card the user interface and signal processing software runs on the users computer rather than on an embedded computer as in the case of a conventional dso related instruments a large number of instruments used in a variety of technical fields are really oscilloscopes with inputs calibration controls display calibration etc specialized and optimized for a particular application examples of such oscilloscopebased instruments include waveform monitors for analyzing video levels in television productions and medical devices such as vital function monitors and electrocardiogram and electroencephalogram instruments in automobile repair an ignition analyzer is used to show the spark waveforms for each cylinder all of these are essentially oscilloscopes performing the basic task of showing the changes in one or more input signals over time in an xy display other instruments convert the results of their measurements to a repetitive electrical signal and incorporate an oscilloscope as a display element such complex measurement systems include spectrum analyzers transistor analyzers and time domain reflectometers tdrs unlike an oscilloscope these instruments automatically generate stimulus or sweep a measurement parameter history oscilloscope history the braun tube was known in 1897 and in 1899 jonathan zenneck equipped it with beamforming plates and a magnetic field for sweeping the trace after world warii surplus electronic parts became the basis of revival of heathkit corporation and a 50 oscilloscope kit made from such parts was a first market success eye pattern phonodeik tennis for two an oscilloscope game timedomain reflectometry vectorscope waveform monitor us 2883619 kobbe john r william j polits electrical probe issued april 21 1959 tektronix 1983 tek products tektronix tektronix 1998 measurement products catalog 19981999 tektronix wedlock bruce d roberge james k 1969 electronic components and measurements prenticehall pp150152 isbn0132504642 us 3532982 zeidlhack donald f richard k white transmission line termination circuit issued october 6 1970 wikimedia commons has media related to oscilloscopes the wikibook school science has a page on the topic of demonstrating the properties of waves on an oscilloscope xyz of oscilloscopes tektronix 64 page tutorial oscilloscope fundamentals primer rohde schwarz using an oscilloscope oscilloscope basic guide oscilloscope tutorial videos digital storage oscilloscope measurement basics low cost oscilloscope utilizing trs connector 35 mm jack oscilloscope development 19431957 the cathode ray tube site oscilloscope history and development milestones 1890today oscilloscope online demo online oscilloscope simulator javascript no plugins required virtual oscilloscope museum vteelectrical and electronic measuring equipmentmetering ammeter capacitance meter distortionmeter electricity meter frequency counter galvanometer lcr meter microwave power meter multimeter megohmmeter ohmmeter peak meter peak programme meter psophometer q meter timedomain reflectometer timetodigital converter transistor tester tube tester wattmeter voltmeter vu meter analysis bus analyzer logic analyzer network analyzer oscilloscope signal analyzer spectrum analyzer waveform monitor vectorscope videoscope generation arbitrary waveform generator digital pattern generator function generator signal generator videosignal generator vteoscilloscopesconcepts types history digital storage oscilloscope waveform monitor vectorscope storage tube manufacturers atten bk precision fluke hameg hantek instek kikusui lecroy micsig keysight pico tech rigol sainsmart siglent sinometer tektronix tiepie engineering yokogawa velleman software picoscope authority control bnf cb11932907v data gnd 40441416 lccn sh85021031 nara 10676191 ndl 00575468 