U1562.pdfU1562pdf,Keysight U1562A无源探头可兼容U1600A系列手持

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详细说明：U1562pdf,Keysight U1562A无源探头可兼容U1600A系列手持式数字示波器。03 Keysight Eight Hints for Better Scope Probing- Application Ncte Hint #1 Passive or active probe? For general-purpose mid-to-low-frequency Yellow: Signal before probed Yellow: Signal before probed Green: Signal after probed Green: Signal after probed (less than 600-MHz)measurements. Purple: Output of probe Purple: Output of probe passive high-impedance resistor divider probes are good choices. These rugged and inexpensive tools offer wide dynamic range (greater than 300 V)and high input resis tance to match a scopes input impedance However, they impose heavier capacitive loading and offer lower bandwidths than Figure 1-1. Comparison of passive and active probe measuring a s gnal that has a low-impedance(z0) passive probes or 600 psec rise time active probes. All in all, high-impedance Keysight N2873A 500-MHz passive passive probes are a great choice for gener- with 15-cm alligator ground leag ve probe Keysight N2796A 2GHz active probe with 1.8-cm ground lead al-purpose debugging and troubleshooting Signal loaded, now has 740 psec edge Signal unaffected by probe, still has on most analog or digital circuits Probe output contains resonance and 630 psec edge For high-frequency applications ( greater measures 1. 4 nsec edge Probe output matches signal and than 600 MHz) that demand precision measure 555 psec across a broad frequency range, active In Figure 1-1 we see screen shots from a The inductive and capacitive effects of the probes are the way to go. They cost more 600 MHz scope the Keysight Technologies, passive probe also cause overshoot and than passive probe and their input voltage is limited, but because of their significantly Inc DSO 9064A)measuring a signal that ripping effects in the probe output ( purple has a 500 psec rise time. On the left, a trace). Some designers are not concerned lower capacitive loading they give you more accurate insight into fast signals Keysight N2873A 500 MHz passive probe about this amount of measurement error was used to measure this signal On the For others this amount of measurement right, a Keysight N2796A 2 GHz single error is unacceptable ended active probe was used to measure the same signal. the yellow trace shows We can see that the signal is virtually the signal before it was probed and is the unaffected when we attach an active probe same in both cases. The green trace shows such as Keysight's N2796A 2 GHz active the signal after it was probed, which is the probe to the dUt. The signal's character- same as the input to the probe. The purple istics after being probed (green trace)are trace shows the measured signal, or the nearly identical to its un- probed character output of the probe istics(N2796A 2 GHz trace). In addition, the rise time of the signal is unaffected by the A passive probe loads the signal down probe being maintained at 555 psec. Also, with its input resistance, inductance and the active probes output (green trace capacitance(green trace). You probably matches the probed signal (purple trace) expect that your oscilloscope probe will not and measures the expected 600 psec rise affect your signals in your device under test time. Using the 1156A active probe's 2 GHz (DUT). However, in this case the passive bandwidth with superior signal fidelity and probe does have an effect on the dut. the low probe loading makes this possible probed signals rise time becomes 4 ns instead of the expected 600 psec, partly due to the probes input impedance, but also due to its limited 500-Mhz bandwidth in measuring a 583-MHz signal (0.35, 600 psec =583 MHz) 04 Keysight I Eight Hints for Better Scope Probing- Application Ncte Hint #2 Key differences between passive and active probes are summarized below in Figure 1-2 High Impedance Passive Probe Active Probe Probe loading check with Power requirement NO YES two probes Loader Heavy capacitive loading and Best overall combination of low Resistive loading resistive and capacitive loading Bandwidth up to 700 MHz up to 30 GHz Applications General purpose mid-to-low High-frequency applications frequency measurements Ruggedness Very rugged Less rugged Max input voltage 300V ~40V Typical Pri S100S500 Slk F gure 1-2 Compariscn of high-impedance passive and active probes Before probing a circuit, connect your To check the probe loading ettect, first, 00s2000/Aut probe tip to a point on your circuit and then connect one probe to the circuit under test connect your second probe to the same or a known step signal and the other end to point Ideally, you should see no change the scope s input Watch the trace on the Signal measured on your signal. If you see a change, it is scope screen, save the trace and recall it wwc probes caused by the probe loading on the screen so that the trace remains on the screen for a comparison. Then, using In an ideal world, a scope probe would be a another probe of the same kind, connect non-intrusive(having infinite input resis to the same point and see how the original tance, zero capacitance and inductance) trace changes over the double probing Wire attached to the circuit of interest Fig 2-1. Probe loading check with twc probes and it would provide an exact replica of You may need to make adjustments to your the signal being measured. But in the probing or consider using a probe with real world, the probe becomes part of the lower loading to make a better measure measurement and it introduces loading to ment. For instance, in this example the circuit shortening the ground lead did the trick. In Figure 2-2, the circuit ground is probed with a long 18 cm(7) ground lead Figure 2-2. Probe loading caused by a long ground lead 5 Keysight Eight Hints for Better Scope Probing- Application Ncte Hint#3 Compensate probe betore use Most probes are designed to match the inputs of specific oscilloscope models However, there are slight variations from scope to scope and even between different o ede s input channels in the same scope. Make sure you check the probe compensation Figure 2-3 Reduced probe loading with short grourd lead when you first connect a probe to an oscilloscope input because it may have In Figure 2-3, the same signal ground been adjusted previously to match a is probed with a short spring- loaded different input. To deal with this. most ground lead. The ringing on the probed passive probes have built-in compensation signal (purple trace)went away with RC divider networks. Probe compensation the shorter ground lead is the process of adjusting the rc divider so the probe maintains its attenuation ratio over the probes rated bandwidth If your scope can automatically compensate for the performance of probes, it makes igure 3-1. Use a small screw driver to adjust the probe's variable capacitance sense to use that feature. otherwise, use manual compensation to adjust the probes variable capacitance. Most scopes have a Probe Tip square wave reference signal available on Cable Probe body Scope the front panel to use for compensating the probe. You can attach the probe tip to the probe compensation terminal and connect Comp 9 MQ the probe to an input of the scope. viewing the square wave reference signal, make the proper adjustments on the probe using a small screw driver so that the square waves on the scope screen look square Figure 3-2. Compensation adjustment corresponds to the f at square wave The diagram at the top of figure 3-2 shows low-frequency adjustment is not properly how to properly adjust the compensating made. This will result in high-frequency capacitor in the termination box at the Inaccuracies in your measurements end of the probe. As you can see in the It's very important to make sure picture, you can have either overshoot or this compensation capacitor is undershoot on the square wave when the correctly adjusted 06 Keysight Eight Hints for Better Scope Probing- Application Ncte Hint 4 Unfortunately, this approach is not The new N2820A Series high-sensitivity appropriate for measuring small currents current probes from Keysight technologies ow current measurement tips that rapidly change between sub-mil address the need for high-sensitivity current amps and several amps because of the measurements with a wide dynamic range limited dynamic range and sensitivity of These probes also offer the advantage of As modern battery-powered devices and integrated circuits become more green and the clamp-on type current probe, which is physically small connections to the device energy efficient, there is a growing need limited to a few milli amps. In the example under test (DUT) since today's application to make high sensitivity low level current for measuring the current consumption of a environments require an extremely small measurements to ensure these devices mobile phone, the idle state current is not form factor. The new N2820A/21A AC/DC current consumption is within acceptable quite measurable because it is buried in the current probes offer the industry s highest limits. The key applications calling for probe noise sensitivity among oscilloscope current probes, going all the way down to 50 uA accurate power consumption measurement are battery-powered applications such as Also, for a more accurate measurement with a maximum current range of 5 A wireless mobile devices and consumer one would occasionally degauss the probe electronics. To maximize the battery lite to remove residual magnetism from the engineers need to minimize the power con probe core and compensate for any dc off sumption over the lite of the product Power set of the clamp-on current probe. T his extra is defined as p=v x l. the key enabler of calibration procedure makes the clamp-on reducing the power consumption of a device current probe cumbersome to use is to lower the average current consumption for a fixed supply voltage level Transmit ]current pulses a primary challenge in measuring the current consumption of battery-powered mobile devices, such as a cell phone or a tablet computer is that the dynamic Receive curent pulses range of the current signal is very wide The mobile device typically switches back and forth between active states where it 500 mA/div draws very high and fast peak currents and Idle current 2 ms/div an idle or standby current mode, where it 0G06 0004 06 0o10 draws very small DC and Ac currents Figure 4-1. The current drain measured on a GSM cell phone when making a cal Figure 4-1 shows the current drain mea sured on a gSM cell phone when making s a call. The active current peaks as high as 2A. and at idle mode the current drain is extremely small e a simple way to measure a current with an oscilloscope is to use a clamp-on type current probe such as Keysight's 1147B or N2893a to directly monitor the current going into the device Figure 4-2. A simple way to measure a current with an oscilloscope is to use a clamp-on type current probe such as Keysight's 1147B or N2893A 07 Keysight Eight Hints for Better Scope Probing- Application Ncte Keysight's N2820A 2-channel high sensitiv ity current probe comes with two parallel differential amplifiers inside the probe with different gain settings, where the low gain side allows you to see the entire waveform or the zoom out" view of the waveform and the high gain amplifier provides a zoom in"view to observe extremely small current fluctuations, such as a mobile phones idle state. The N2820A/21Acur- rent probes are optimized for measuring the current flow within the dut to characterize sub-circuits, allowing the user to see both ge signals and details on fast and wide dynamic current waveforms Figure 4-3. The new N2820A/71A AC/DC current probes oter the industry s highest sensitivity among oscilloscope current probes The probe offers an innovative method of connecting the probe to your dUT. The supplied Make-Before-Break(MBB)con nectors allow you to quickly probe multiple locations on your DUT without having to solder or unsolder the leads the mbb header may be mounted on your target board or wired out of the dut. lt fits into standard 0. 1"spacing thru- holes for 0.025 square pins. Users should plan their PCB Figure 4-4. The supplied Make-Before-Break layouts accordingly. The MBBs are a great (MBB) connectors al ow you to quickly probe multiple locations on your DUT without having way to easily connect and disconnect to solder or unsolder the leads across multiple locations on the target board without interrupting the circuit under test r Cnrd -tp Trp The innovation hasn t stopped there. With Q自西 current waveforms captured, you now want B四 to calculate the average current consump tion of the system over time. Keysight's Infiniium and Infinii Vision oscilloscopes provide an area under the curve measure ment(Charge), where you can easily calcu- U late the integrated current consumptions in Ah(Ampere x Hour) over time. The Ah is a unit of measurement of a battery s electri- cal storage capacity One Ah is equal to a 山山MLi current of one ampere flowing for one hour Now with the N2820A/21A current probes engineers in battery-powered product test- LEEE ing are able to see the details and the big purrr- picture on dynamic current waveforms like n≌/ never before with traditional clamp on probes Figure 4-5. Keysight's Infiniium and Infinii Vision oscilloscopes provide an area under the curve measurement Charge), where you can easily calculate the integrated current con sumptions in Ah(Ampere x Hour)over time 08 Keysight Eight Hints for Better Scope Probing- Application Ncte Hint #5 Most digital oscilloscopes have a subtract Using a high-voltage differential probe such mode where the two input channels can as Keysight's N2790A is a much better Making sate floating be electrically subtracted to give the solution for making safe, accurate floating difference in a differential signal. For measurements with any oscilloscope. With measurements with a decent results, each probe used should be a true differential amplifier in the probe differential probe matched and compensated before using it head, the n2790a is rated to measure In this method, the common mode rejection differential voltage up to 1, 400 VDC Scope users often need to make floating ratio is typically limited to less than -20db peak ac with Cmrr of -70 dB at 10 MHz measurements where neither point of the (10: 1 ) If the common mode signal on each Use a differential probe with sufficient measurement is at earth ground potential probe is very large and differential signal is dynamic range and bandwidth for your For example, suppose you measure a much smaller, any gain difference between application to make sate and accurate voltage drop across the input and output the two sides will significantly alter their floating measurements of a linear power supply's series regulator differential" or A-B"result. a good sanity U1. Either the voltage in or out pin of the check here would be to double probe the regulator is not referenced to ground same signal and see what the A-B shows them A standard oscilloscope measurement where the probe is attached to a signa point and the probe tip ground lead is attached to circuit ground is actually a measurement of signal difference between BRI OUT+ the test point and earth ground. Most Ad scopes have their signal ground terminals C1 C4 or outer shells of the bNc interface) connected to the protective earth ground system. This is done so that all signals Ground applied to the scope have a common connection point. Basically all scope Figure 5-1. When measurement is not ground referenced, a differential measurement solution measurements are with respect to earth Is necessary. ground. Connecting the ground connector to any of the floating points essentially 120V/2200V/ 0.0s200.0 Stop f1,22y pulls down the probed point to the earth ground, which often causes spikes or malfunctions on the circuit. How do you get around this floating measurement problem a popular yet undesirable solution to ti need for a floating measurement is the A-B technique using two single-ended probes and a scope's math function 2 d/dt ∫dt Menu tFunction Offset 100mV/ 109m Figure 5-2. As a sanity check, double probe the same signal and see what the "A-B looks like 09 Keysight Eight Hints for Better Scope Probing- Application Ncte Hint #6 One of the most misunderstood issues with ground and onto the probe cable shield probing is that common mode rejection can Sources of common mode noise can be Check the common limit the quality of a measurement With internal to the dut or external to it such either a single-ended or differential probe, it as power line noise, EMI or ESD currents mode rejection is always worthwhile to connect both probe tips to the ground of the dut and see if any a long ground lead on a single-ended signals appear on the screen probe can make this problem very significant. A single-ended probe If signals appear, they show the level of does suffer from lack of common signal corruption that is due to lack of mode rejection. Differential active common mode rejection Common mode probes provide much higher common noise currents caused by sources other mode rejection ratios, typically as high than the signal being measured can flow as 80 dB (10,000: 1) from ground in the dut through the probe Figure 6-1. Connect both probe tips to the ground and see if any signals appear on the screen Transmission Output 多Q多几 Figure 6-2. Differential active probe provides much higher common mode rejection ratic effectively elim nating common mode ncise current Hint #7 The position of the ferrite core on the cable is important. For convenience, you Check the probe coupling may be tempted to place the core at the scope end. This would make the probe head lighter and easier to handle. However With your probe connected to a signal. the core 's effectiveness would be reduced move the probe cable around and grab it with your hands. If the waveform on the substantially by locating the core at the probe interface end of the cable screen varies significantly, energy is being coupled onto the probe shield, causing this variation Using a ferrite core on the Reducing the length of the ground lead on a single-ended probe will help some probe cable may help improve probing Figure 7-. Using a ferrite core on the probe accuracy by reducing the common mode Switching to a differential probe will cable may help improve probing accuracy noise currents on the cable shield a ferrite typica lly help the most. Many users don t understand that the probe cabl core on the probe cable generates a series impedance in parallel with a resistor in the environment can cause variations in conductor The addition of the ferrite core their measurements, especially at higher frequencies, and this can lead to frustration to the probe cable rarely affects the signal with the repeatability and quality of because the signal passes through the measurements core on the center conductor and returns through the core on the shield, resulting in no net signal current flowing through the core 10 Keysight Eight Hints for Better Scope Probing- Application Ncte Hint #8 If you have to add wires to the tip of a be determined by first probing a known probe to make a measurement in a tight step signal through a fixture board like the Damp the resonance environment, put a resistor at the tip to Keysight E2655C into a scope channel damp the resonance of the added wire Then probe the signal with your proposed wire with a resistor at the tip When the The performance of a probe is highly For a single-ended probe, put the resistance resistance value is right, you should see a affected by the probe connection. as only on the signal lead and try to keep the step shaped much like the test step, except the speeds in your design increase, you ground lead as short as possible For a it may be low-pass filtered If you see nay notice more overshoot, ringing, and differential probe, put resistors at the tip excessive ringing, increase the other perturbations when connecting an of both leads and keep the lead lengths resistor value oscilloscope probe Probes form a resonant the same. The value of the resistor can circuit where they connect to the device. If this resonance is within the bandwidth of the oscilloscope probe you al it will be difficult to determine if the measured perturbations are due to your circuit or the p Figure 8-1. Put a resistor at the tip to damp the resonance of the added wire Undamped Damped Zsr匙 2 Inch lead Inch lead VIn Figure 8-2. With a properly damped probe input, the loading/input impedance will never drop below the value of the damping resistor Z5OMHz Clock, 100ps Rise Time Undamped:j Damped Vs source HH H+++I++++++++H +H++++H+H+ Vin Vout ---:-1500ps/div--1 :500ps/div Figure 8-3. As the speeds in your design increase, you may notice more overshoot, ringing and other perturbations Overcome the resonance formed by the connection of a probe by adding a damp resistor to your probe tip

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