1. For a finished product, how can an oscilloscope be used to test and analyze reliability?
Answer: The oscilloscope is one of the most effective tools for testing electronic circuits. Observing voltage and current waveforms at key circuit nodes allows direct verification of correct operation and design validity, which helps improve reliability. Correct waveform analysis depends on the engineer's experience.
2. What are the main factors that determine oscilloscope probe price?
Answer: Probes vary widely: high-voltage, differential, active high-speed, etc., with prices from a few hundred yuan to nearly ten thousand dollars. The main determinants are bandwidth and features. The probe is the circuit-facing part of the oscilloscope; a good probe preserves test fidelity. Even passive probes contain compensation networks of many passive components (RC networks) to achieve this.
3. What is the typical service life of standard probes and do probes need periodic calibration?
Answer: Probe life depends on usage and environment. Standards do not strictly define probe calibration intervals, but for passive probes you should adjust probe compensation when changing probes or channels. Active probes should warm up at least 20 minutes before use; some active and current probes require zero-offset adjustments.
4. What is real-time sampling rate of an oscilloscope?
Answer: Real-time sampling rate is the reciprocal of the sampling interval for a single acquisition (one trigger). The industry’s top levels support simultaneous high sampling on multiple channels.
5. What is equivalent-time sampling?
Answer: Equivalent-time sampling reconstructs a waveform from many acquisitions (many triggers). Each acquisition samples slowly, with a small trigger offset between acquisitions; the reciprocal of the smallest effective sample interval between the reconstructed points is the equivalent sampling rate, which can reach very high values, e.g., 1 ps.
6. What is power factor and how is it measured?
Answer: In DC circuits, voltage times current equals real power. In AC circuits, voltage times current is apparent power; the portion that performs work is real power. The ratio of real power to apparent power is the power factor, often expressed as cos phi. The simplest measurement is the phase difference between voltage and current.
7. How is power density expressed and tested?
Answer: Power density is power per unit volume. In power supplies it is commonly expressed in W/in3.
8. Is there a way to use an oscilloscope to assess a high-frequency transformer or inductor core?
Answer: Some power test solutions provide B-H curve analysis, which reflects core operating state, dynamic inductance, and core loss.
9. Switch-mode power supply noise can come from layout crosstalk, inductor leakage, diode reverse spikes, etc. How to distinguish noise sources with an oscilloscope?
Answer: Frequency-domain analysis on an oscilloscope helps identify the frequency bands of the noise, which aids classification and appropriate mitigation. The oscilloscope provides data and band displays for analysis.
10. How can an oscilloscope detect radiated emissions from a switching power supply?
Answer: Radiated interference can be located, then shielded. The oscilloscope's FFT capability analyzes frequency components; knowing the frequency range helps infer the interference type.
11. In flyback supply design, transformer leakage inductance can reduce efficiency. Are there winding techniques to reduce leakage?
Answer: Wind high-power output windings inside and as close as possible to the primary to strengthen coupling.
12. Is there an oscilloscope solution that analyzes switching losses?
Answer: Power analysis systems combining a digital phosphor oscilloscope and power-analysis software can analyze switching losses and per-cycle power loss, including RDS(on).
13. Can oscilloscopes perform Fourier decomposition?
Answer: Modern digital oscilloscopes generally include FFT functions; some systems can perform pretests of current harmonics per EN 61000-3-2.
14. Can an oscilloscope perform filtering, such as low-pass filtering of PWM?
Answer: Some models support 20 MHz and 150 MHz low-pass filtering and high-resolution acquisition (digital low-pass) modes. In high-resolution mode vertical resolution can be increased from 8 bits to 12 bits, allowing reconstruction of slowly varying envelope-like waveforms from PWM signals.
15. When using a digital oscilloscope, what are principles for setting A/B triggers and trigger levels relative to the measured signal?
Answer: A/B trigger feature enables dual-event sequence triggering. In A-B sequence mode, A is the master trigger and B captures complex waveforms. The A event arms the trigger system; when the B event occurs, the scope triggers at the B event. See the oscilloscope manual for detailed trigger descriptions.
16. How to measure the peak of a modulated waveform with carrier frequency of tens of kHz and modulation at mains frequency using a TDS3052B?
Answer: For a mains cycle of around 20 ms, the acquisition window must cover that duration, e.g., 2 ms/div × 10 divisions for 20 ms. Choose the oscilloscope sampling rate according to the tens of kHz carrier. Estimate required memory depth to confirm the capture fits.
17. Using a nominal 100 MHz DSO to measure a high-voltage switching signal of 400 V amplitude at f=50 MHz, how will the scope depict waveform and rise time?
Answer: 1) Bandwidth is defined at the -3 dB amplitude point for sine waves. 2) Digital scopes obtain waveform and rise-time data via real-time sampling circuits and high-speed A/D converters, with interpolation used to reconstruct the waveform. 3) Some scopes implement sinusoidal interpolation in hardware. 4) A 100 MHz scope is inadequate for a 50 MHz square wave. Accurately reconstructing harmonics up to the 9th requires a scope with >450 MHz bandwidth; rise-time measurement requires the oscilloscope rise time to be at least five times faster than the signal. 5) Probes matter: for high-voltage fast signals use differential or high-voltage probes such as dedicated HV probes.
18. How to use a digital oscilloscope effectively for analog circuits, e.g., measuring small audio amplifier signals or power supply ripple?
Answer: Key considerations: 1) Grounding: chassis and probe ground are connected to earth; good grounding is essential. 2) Probe ground lead induced noise: the ground lead can form a loop antenna. For low-noise measurements remove the long ground lead and use the probe tip and ground reference close to the test point. 3) Use differential measurement to remove common-mode noise; specialized differential probes provide high sensitivity and bandwidth. 4) Use high-resolution capture (Hi-Res) modes to filter random noise.
19. When measuring conducted emissions on an off-board signal line, large noise appears at two frequencies (e.g., 659 kHz and 1.977 kHz). How to measure such noise with an oscilloscope?
Answer: Consider signal amplitude (is it a small signal?); frequency of the noise; and probe connection method—improper probe connection can introduce noise and affect results.
20. What does Holdoff mean on an oscilloscope?
Answer: Holdoff temporarily disables the trigger circuitry for a set time. During this interval the scope will not trigger even if trigger conditions are met. On digital scopes holdoff is often expressed as a percentage of the record length or display. Holdoff stabilizes display by preventing triggers on repeatable but undesired points within a long period, ensuring consistent trigger position. It is also useful for modulated signals.
21. Regarding holdoff, what is the difference between triggered and non-triggered acquisitions?
Answer: Digital scopes continuously acquire waveform data whether they are triggering or not, but stable display requires a stable trigger. In "Auto" mode the scope displays waveforms regardless of trigger condition; in "Normal" mode the scope displays only when the trigger condition is met.
22. If horizontal resolution is unchanged, does a larger holdoff percentage imply a longer signal period?
Answer: Yes. Larger percentage means longer holdoff time.
23. How to measure differential signals with an oscilloscope?
Answer: Use a differential probe for best fidelity. Without one, use two identical probes on two channels and compute the difference (Ch1 ? Ch2) via math. Keep probes and channel vertical scales identical to minimize error.
24. How to measure differential signals on the USB bus?
Answer: Two cases: 1) For compliance tests per USB physical-layer specifications (USB 1.1/2.0) many protocol and signal-quality tests are required (signal quality, droop & drop, inrush, HS-specific tests, chirp, monotonicity, receiver sensitivity, impedance/TDR, etc.). 2) For basic observation, use a suitable differential probe connected to D+, D? to observe USB signals. USB 2.0 has very fast edges (rise times of a few hundred picoseconds); use >2 GHz oscilloscope and differential probe to preserve fidelity.
25. For PCB high-speed signals such as XAUI 3.125 GBd serial differential signal with 60 ps rise time, what bandwidth is needed and what measurement error is expected?
Answer: For 100 ps–130 ps rise times, a 7 GHz differential probe can keep error <3%. For <80 ps rise times, error rises above 10%. For highest accuracy in rise-time measurement, a network analyzer with bandwidth up to tens of GHz is ideal.
26. For designs with stringent clock phase-noise requirements, what key issues reduce phase noise?
Answer: In ADC and DAC circuits, many performance metrics matter (resolution, conversion speed, DC accuracy, switching performance, dynamic metrics such as SNR, SINAD, IMD). Clock phase noise affects these dynamic metrics and should be minimized via careful clock-source selection, power supply filtering, and jitter control.
27. How to measure phase noise?
Answer: Oscilloscopes can measure analog and digital amplitudes and timing, conversion performance, setup/hold margins, and with spectral analysis functions can qualitatively assess SNR and SINAD. For detailed phase-noise measurements specialized instruments or jitter-analysis options are typically used.
28. If an external clock must be selected from two sources, how to minimize phase-noise degradation?
Answer: Analyze jitter sources. Oscilloscopes with dedicated jitter analysis software can separate deterministic jitter (Dj) and random jitter (Rj) and help locate causes to mitigate jitter.
29. What is the difference between external trigger and internal trigger when viewing waveforms?
Answer: Typical trigger is edge trigger with trigger level and edge direction. Use external trigger when the signal’s complexity produces multiple valid trigger points and the internal trigger cannot provide a stable display. External triggers can synchronize the scope to a chosen reference signal to obtain stable, full-period displays.
30. A TDS3032B has 300 MHz bandwidth and 2.5 GSa/s sampling, an 8:1 sampling-to-bandwidth ratio. Is there a fixed relationship between bandwidth and sampling rate, and why do different scopes have different ratios?
Answer: Bandwidth is the fundamental spec, defined by the analog front end at -3 dB. Nyquist sampling theorem requires at least two samples per cycle, but practical waveform reconstruction depends on interpolation algorithms and other factors. Advanced reconstruction algorithms can reconstruct waveforms with fewer samples per cycle (e.g., 2.5 samples), while simple linear interpolation may require more. Typical advice is sampling rate 4–5 times the bandwidth for accurate waveform reproduction. Some scopes specify realtime (single-shot) bandwidth differently; check the vendor datasheet for single-shot vs. repetitive-signal characteristics.
31. How should bandwidth in oscilloscope specifications be interpreted?
Answer: Bandwidth is the -3 dB frequency. A 100 MHz scope measuring a 100 MHz sine will show 0.707 times the real amplitude. To achieve measurement accuracy, choose bandwidth about five times the highest signal frequency.
32. How to obtain the total system bandwidth of a measurement setup?
Answer: For oscilloscopes below 1 GHz, an approximate formula is Total system bandwidth = 0.35 / rise time.
33. If bandwidth is fixed, is excessively large sampling rate pointless?
Answer: Bandwidth limits capture of high-frequency components. With suitable reconstruction algorithms, a few samples per cycle can be sufficient, but other scopes may require more. Matching scope architecture and sampling rate to application is important.
34. What are Gaussian-response and flat-response oscilloscopes, and their pros and cons?
Answer: The front-end frequency and phase response determine measurement results. Bandwidth is increasingly high in modern scopes. Some vendors use DSP to extend or enhance response; DSP can improve apparent bandwidth and waveform fidelity but can introduce tradeoffs. Understand whether the quoted bandwidth refers to analog front-end bandwidth or DSP-enhanced bandwidth; some scopes allow DSP enhancement to be enabled or disabled to show both behaviors.
35. Besides Gaussian and flat responses, are other response types used?
Answer: The analog front-end frequency response method is key; different implementations obtain the required response. The specific approach depends on analog design choices.
36. After switching from passive probes (e.g., P6139A) to active probes (e.g., P6237), measured waveforms differ significantly, especially for high-frequency signals. Why, and how to choose between active and passive probes?
Answer: Passive probe input capacitance differs from active probes, affecting loading and ringing. Passive probes with higher input capacitance can load the circuit and distort high-frequency signals. When measuring high-speed signals consider bandwidth/rise time, dynamic range, loading effect, grounding, and resonance. Shorten the ground lead on passive probes. Active differential probes offer high fidelity but limited dynamic range and different common-mode characteristics. Choose probes based on required voltage range, dynamic range, bandwidth, and loading.
37. During experiments, connecting a scope ground caused a MOSFET to be destroyed, so the ground lead was cut off. Why did this happen?
Answer: Probe ground and chassis are earth-referenced. If probing a node that is not at earth potential, connecting the probe ground can create a short. Cutting the ground lead prevents that short but introduces safety and measurement fidelity issues. Use differential or high-voltage probes that allow safe measurement of floating nodes.
38. When capturing data, saved text contains only the current screen data at resolution intervals. How to process data in real time (e.g., with MATLAB) and capture more data?
Answer: Some oscilloscopes use compressed screen displays, but full acquisition data are stored internally. Use multiView/zoom features and the instrument's Windows platform or connectivity (MATLAB, LabVIEW, VB, .NET, VBA) to extract data. Increasing single-shot capture memory depth allows longer captures; some models support deep memory (e.g., up to 16M points).
39. What factors affect an oscilloscope’s operating speed?
Answer: Both front-end data acquisition and back-end processing affect speed. Data transfer between acquisition and processing (often via PCI) can be a bottleneck; back-end processing approaches such as data packetization can improve throughput.
40. For applications that capture 2M or more points at up to 10 GSa/s, parameter testing and FFT are slow. Why?
Answer: Large data volumes slow processing. Real-time high-rate FFT requires specialized FFT processors to speed analysis, which increases cost.
41. Using a TDS2014 to capture a parallel port timing, the scope always shows a strong 50 Hz signal instead of the actual signal, though ground references match. What to do?
Answer: Check: 1) scope grounding and use of isolation transformer if needed; 2) nearby strong 50 Hz sources; 3) driver strength and operating frequency of the parallel port; 4) probe tip condition; 5) disconnect unnecessary peripherals which might inject noise; 6) check probe ground clip continuity with a multimeter.
42. When measuring power-supply interference coupled into a sensitive amplifier, the oscilloscope shows the same audio-frequency interference everywhere even when probe ground is connected. Why?
Answer: Consider: 1) grounding quality; 2) probe ground lead forming a loop antenna—remove long ground lead and probe close to the reference point; 3) use differential measurements to reject common-mode noise with high-CMR differential probes; 4) use high-resolution acquisition modes to filter random noise.
43. During EMC EFT testing the oscilloscope display can wobble and indicators can briefly disappear. How to explain and mitigate this?
Answer: EFT can interfere with the oscilloscope, causing false triggers. Use high-frequency trigger suppression modes and bandwidth limiting to reduce false triggering.
44. Why can an oscilloscope sometimes fail to capture amplified current signals?
Answer: Intermittent capture often relates to scope settings. Set trigger mode to Normal, edge trigger, adjust trigger level appropriately, and use single-shot capture to capture sporadic events. If issues persist the instrument may be faulty.
45. How can modern oscilloscopes be used in microcontroller development?
Answer: Microcontroller circuits commonly have communication buses like SPI, I2C, USB, LIN, CAN. Oscilloscopes with serial decode and trigger functions can debug bus-level communications. Mixed-signal scopes with digital logic channels help correlate control, data, and address lines, and deep memory aids long-duration captures and handshake analysis. High channel sensitivity enables observation of small signals.
46. Do digital oscilloscopes 54621A and 54621D affect Inter-IC bus signals at different speeds?
Answer: I2C typically runs ≤400 kbit/s and newer parts run higher. When setting trigger conditions these scopes generally handle different speeds; for buses like CAN, set the actual bus bitrate so the scope can decode protocol and trigger correctly.
47. Besides oscilloscopes 54621A and 54621D, what other instruments can analyze Inter-IC bus signals?
Answer: For protocol-level analysis, a logic analyzer provides deeper protocol decoding but usually at higher cost than the mentioned scopes.
48. Which trigger types suit which signals: edge, glitch, pulse-width, etc.?
Answer: Edge trigger is the basic trigger (rising or falling). Advanced triggers allow specialized conditions for locating features of interest and are key for debugging. High waveform capture rates combined with advanced triggers help locate and diagnose intermittent faults quickly.
49. Regarding glitch capture, is the smallest glitch the scope can capture determined solely by sampling rate? Does the front-end filter affect it?
Answer: Not solely. Glitch capture ability depends on bandwidth, sampling rate, and waveform capture rate (how many waveforms per second the scope can capture). Front-end filtering also affects detectability. High capture rates and appropriate front-end bandwidth are critical for glitch capture.
50. How to eliminate glitches when using an oscilloscope?
Answer: If the glitch is inherent in the signal and you want to synchronize to it, use high-frequency trigger suppression or pulse-width triggers. If you want the scope to ignore glitches, bandwidth limiting can suppress them but may also attenuate desired signal components. Logic analyzers with state capture can sometimes hide such glitches depending on sampling mode.
51. How to capture and test sporadic glitches?
Answer: Use fast waveform capture modes with infinite persistence to observe glitch characteristics, then use a pulse-width trigger set narrower than normal pulse width to capture the anomalous pulses.
52. Typical applications of glitch/pulse-width triggers?
Answer: 1) Synchronizing in noisy or complex signals where edge trigger fails; 2) Finding rare anomalies like narrow spikes or timing faults. Use pulse-width triggers set to short durations (e.g., 10 ns–30 ns) as needed.
53. Do Keysight digital oscilloscopes have DPO functionality?
Answer: DPO is a vendor-specific term. Keysight offers MegaVision or equivalent features: high waveform-capture rates, direct zoom into anomalies, and enhanced real-time sampling rates with deep memory optimized for certain applications.
54. After computing bandwidth from rise time, is the sampling-rate recommendation solely to avoid aliasing?
Answer: The sampling-rate recommendation aims to avoid aliasing but is a general guideline. Specific test signals and instrument architectures require tailored sampling and bandwidth choices for accurate results.
55. How does an oscilloscope display waveform between two sample points?
Answer: Displays may use point, sinusoidal interpolation, or line-vector connections. Interpolation adds points between samples that are not actually acquired. Pointing or interpolation choices affect required sampling-rate multipliers: vector display may require higher sampling density to avoid visible artifacts; sinusoidal interpolation allows lower sampling ratios to look smooth.
56. For a 156.25 MHz differential clock with rise/fall <100 ps (20%–80%), jitter p-p <30 ps, RMS <2 ps, skew <20 ps, what bandwidth is needed and expected measurement error?
Answer: For 100 ps rise time and 3% accuracy, a system bandwidth around 5.6 GHz is needed; for 10% accuracy around 4.8 GHz. Ensure the entire probe-and-scope system supports the bandwidth. Accurate jitter measurement requires a scope with low intrinsic trigger jitter; high-sampling-rate A/D helps reduce measurement error.
57. When choosing an oscilloscope, when should sampling rate be considered?
Answer: Sampling rate matters depending on the signal. Given sufficient bandwidth, the minimum sampling interval must capture required signal detail. Empirical guidelines exist, but validate by freezing and zooming the waveform: if features change with zoom, sampling rate may be insufficient. Use point-display to inspect actual samples.
58. Why can a 100 MHz analog scope show parasitic waveforms more clearly than a 100 MHz digital scope?
Answer: Analog scopes have continuous electron-beam traces with high refresh and fine lines. Digital scopes sample and map many memory points to limited display pixels, causing apparent line thickness when memory depth is deep. Reduce record length or use point display to see individual samples. Also probe loading and 1:1 vs 10:1 probe settings affect fidelity.
59. Which is better for observing waveform minutiae: analog or digital oscilloscope?
Answer: Observing sub-1% parasitics is challenging for both. Analog scopes are not inherently more vertically accurate; modern digital scopes offer precise automated measurements. Vertical accuracy and instrument specs must be compared for the specific task.
60. Digital scopes provide RMS values on-screen. What is the typical accuracy?
Answer: Amplitude measurement accuracy depends on A/D effective bits, bandwidth, and sampling settings. If bandwidth is insufficient measurement error increases. Overall, oscilloscopes typically have less amplitude accuracy than a good multimeter and frequency measurement is less precise than a frequency counter.
61. How to capture and reproduce fleeting transient signals?
Answer: Use single-shot acquisition with appropriate vertical and horizontal scales and single acquisition trigger. Deep-memory scopes with zoom or pan features allow local detail inspection while preserving context. Memory depth determines capture duration at maximum sampling rate.
62. Which Keysight scope can test a 500 MHz carrier?
Answer: For a sine carrier alone, a 1.5 GHz scope provides significantly better amplitude and rise-time accuracy than a 500 MHz scope. Using BNC connections and suitable probes or active probes is recommended for preserving fidelity.
63. Does a 60 MHz spec mean the scope can measure 60 MHz well?
Answer: Not necessarily. A 60 MHz bandwidth means a 60 MHz sine will be displayed at 0.707 of its true amplitude (30% amplitude error). Bandwidth alone does not guarantee high accuracy at that frequency.
64. Why does a 60 MHz scope sometimes fail to display a 4.1943 MHz square wave?
Answer: Square waves depend on higher harmonics. Probe bandwidth and front-end accessories affect system bandwidth. Some scopes in 1:1 probe mode have lower actual bandwidth. Harmonics at 3rd and 5th orders may be above the effective bandwidth and be attenuated, so the waveform may be sinusoidal or not visible. Verify with a direct BNC connection to a function generator to isolate probe issues.
65. How to measure clock stability?
Answer: Use histogram methods or dedicated jitter analysis tools to measure edge time variation. Dedicated jitter analysis software provides comprehensive techniques for worst-case jitter assessment.
66. What are methods for precisely measuring PLL period jitter with Keysight scopes?
Answer: Use histogram-based measurements or dedicated jitter-analysis software, ensuring the scope's own jitter and probe system meet test requirements. Check trigger jitter and probe/system bandwidth before measurement.
67. How to measure PLL settle time with Keysight instruments?
Answer: A combined oscilloscope and software solution or a modulation-domain analyzer can measure PLL settle time.
68. How to measure PFD (phase-frequency detector) dead zone when designing a PLL?
Answer: Connect one channel to the reference signal and another to the feedback signal. Use setup/hold or edge triggers and adjust until the loop loses lock; the hold/setup setting corresponding to loss of lock indicates the PFD dead zone. Ensure scope bandwidth supports the measurement.
69. How to test optical signals with Keysight equipment?
Answer: Use the full set of optical test instruments (light sources, spectrometers, optical power meters, optical scopes, wavelength meters). For oscilloscope-based measurement, use a photodiode or optical-to-electrical converter with appropriate bandwidth.
70. How to measure power-supply ripple with an oscilloscope?
Answer: Capture the full waveform, then zoom into the ripple portion for measurement. Use FFT for frequency-domain analysis. For best accuracy, adjust vertical scale so the waveform nearly fills the screen, maximize memory depth for frequency resolution, and consider extracting data to MATLAB for deeper analysis. For low-noise measurements use 50 ohm termination and BNC connection rather than high-impedance probe ground leads.
71. How to correctly measure output ripple and noise of a switching supply?
Answer: Ripple is defined as the peak-to-peak deviation on a DC level (PARD). Ground leads on probes introduce significant noise—use 50 ohm termination and BNC with proper power dissipation, or differential/high-CMR probes to avoid ground-loop noise. Follow applicable bandwidth limits from standards if specified.
72. If measured ripple contains strong 50 Hz periodic spikes that grow with load, what remedies exist?
Answer: Separate mains-frequency ripple from switching ripple by selecting filters or measurement modes for the respective frequency bands. Power-analysis systems can separate mains-frequency and switching components for independent measurement.
73. How to remove mains-frequency noise from ripple measurements?
Answer: Use high-resolution capture modes to reduce random noise and select the measurement band to focus on the ripple of interest. Dedicated power-analysis software can separate periodic mains ripple from switching noise.
74. Is a dedicated lab required for precise ripple and noise testing?
Answer: A dedicated lab is ideal. If unavailable: ensure good grounding, apply bandwidth limits required by standards, use AC coupling if appropriate, use BNC and 50 ohm input with proper load, and avoid probe ground clips when possible. Differential measurement and careful test fixtures improve accuracy.
75. How to measure very low ripple, e.g., verify 1.8 V output ripple <20 mV, when probe-ground noise may already be tens of millivolts?
Answer: Use high common-mode-rejection differential voltage probes designed for noisy environments.
76. How to view and read the period of a displayed waveform on a digital scope?
Answer: Use automatic period/frequency measurement. Some scopes include a built-in hardware counter for higher precision. Alternatively, display one cycle full-screen, maximize vertical scale, and use cursors or auto-measurements for precision.
77. During prototyping, audio and data outputs appear correct on the bench but finished products sometimes exhibit intermittent audio issues. Why?
Answer: Often this indicates lack of synchronization between measurement and the device under test. For audio, use rolling mode or capture long durations, stop when the problem occurs, then analyze. Frequency-domain analysis or dynamic signal analyzers may be more appropriate for audio problems. Mixed-signal scopes with logic channels can help correlate digital events and audio anomalies.
78. How to perform jitter testing with a TDS3012?
Answer: Entry-level scopes like the TDS3012 can use long-persistence display to accumulate timing variations, but comprehensive jitter measurement requires scopes with dedicated jitter-analysis software and higher bandwidth. Use higher-bandwidth development platforms for precise jitter tests.
79. How to measure power factor in AC/DC supplies with an oscilloscope?
Answer: Measure the phase difference between line voltage and current to compute cos phi. Integrated power-test systems compute THD, true power, apparent power, and power factor automatically.
80. Can oscilloscope FFT amplitude results be compared directly to certification-center measurements? Do FFT amplitudes vary with V/div?
Answer: Oscilloscope FFT results are qualitative and provide reference insight rather than certification-level quantitative measurements. Choose appropriate windowing (e.g., Blackman-Harris) for better results. Changing V/div affects FFT amplitude because of ADC resolution and should be accounted for; maximize signal amplitude on screen (without clipping) for better FFT precision.
81. Which oscilloscope model improves design efficiency?
Answer: Choose a scope based on the signals you need to observe and analyze. Modern scopes put emphasis on data analysis features that aid design, so pick one that matches your signal types, bandwidth, channels, and analysis requirements.
82. How to test video parameters (output level, horizontal resolution, luminance/chroma amplitude response, SNR, nonlinearity, etc.) with an oscilloscope?
Answer: Use oscilloscopes with video measurement options, vector scope functionality, and built-in video formats. Certain series and software options provide analog HDTV and other video analysis features.
83. At high frequency, how to judge probe impedance effect on the signal?
Answer: Use probe equivalent impedance versus frequency charts to determine the probe’s load at each frequency. Follow probe application notes for correct usage.
84. Why does a Tek oscilloscope show more ringing on a 30 MHz clock than an Agilent scope using a 250 MHz probe?
Answer: Measurement setup and scope settings affect ringing. Use appropriate auto-trigger, resolution, sampling multiple of signal frequency (e.g., 10×), and proper probe compensation. For power-device measurements choose Vds and Ids on MOSFETs or Vce and Ice on IGBTs, and use power-analysis software as needed. Proper probe selection and connection are essential.
85. For soft-switching PWM converters (e.g., half-bridge), how to observe MOSFET V-I trajectories?
Answer: Use inter-channel skew correction and measure with high-voltage differential voltage probes and current probes. Power-test solutions can dynamically display device operating trajectories.
86. Should output inductance and capacitance values be chosen strictly from datasheet formulas, and how to adjust if problems occur?
Answer: Component selection depends on topology; choose formulas appropriate to the chosen topology. Output capacitance is sized to meet ripple specifications and ESR constraints. Consider load variations, current ranges, and dynamic behavior; adjust component values based on empirical testing.
87. HID xenon lamp ballast designs sometimes fail to ignite due to slow high-voltage recovery. How to address this?
Answer: Control the secondary breakdown process and measure primary and secondary breakdown pulse peaks and widths using long record single-shot capture. Compare timing and amplitude of breakdown events to design requirements and adjust the ballast control or circuit accordingly.
88. What is the fundamental difference between a Windows-based oscilloscope and virtual-instrument (PC-based) solutions?
Answer: Windows-based scopes integrate a dedicated acquisition and processing unit optimized for reliable instrument performance, with Windows serving as a user interface. Virtual instruments rely on PC acquisition cards and the host CPU for processing; they are lower cost but can have reproducibility and traceability issues due to host variability.
89. How to reduce DC-DC transformer thermal loss and what design considerations and peripheral requirements exist?
Answer: Follow flux-reset principles, select core size and material based on power, calculate primary inductance and turns, and test for worst-case saturation. Proper winding, core selection, and thermal design are required.
90. For switch-mode power supplies, switching device losses largely determine efficiency. When measuring switch waveforms with an oscilloscope, what practices and precautions apply?
Answer: Measure turn-on, turn-off, and conduction losses; measure transformer and inductor core losses and dynamic inductance. Use appropriate differential voltage and current probes and account for probe and scope bandwidth, timing skew, and measurement calibration to obtain accurate loss estimates.
91. How to test and analyze switching oscillation and video signals?
Answer: Use scopes with suitable capture and analysis features. For switching supplies, power-analysis suites can track duty-cycle and frequency trends. For video, use video-specific triggers and measurement modes to analyze fields and frames.
92. Is there a general transformer design method for flyback converters?
Answer: Theoretical calculations provide a starting point, but variations in core and winding methods require iterative testing. Start with primary inductance calculation, choose core based on power, and ensure flux reset in single-ended designs.
93. Using TDS3032B and THS710, how to capture and store a single random event fully for later analysis?
Answer: For single-shot events configure appropriate vertical/horizontal scales and single acquisition trigger, then save the waveform to reference memory. For anomalies within repetitive signals, use fast display and infinite persistence to find features, then use single acquisition to capture them.
94. Are there special requirements for switching power supplies starting at low temperatures (e.g., < ?20 °C)?
Answer: Component operating temperature ranges are critical, especially capacitors, MOSFETs, and diodes. Select devices rated for the target temperature range.
95. How to reduce EMC emissions while preventing susceptibility to external interference?
Answer: EMC depends on source, coupling path, and victim. Mitigate by reducing generated interference, interrupting propagation paths, and increasing immunity. Techniques include improving input/output filtering, optimizing PCB layout and grounding, reducing loop areas, improving chassis shielding and gaskets, and employing surge protection (e.g., MOVs and gas discharge tubes) where appropriate. Proper digital/analog partitioning, single-point grounding for sensitive circuits, careful routing, and component selection are key.
96. From what data is SOA testing derived and which oscilloscope measurements can obtain it?
Answer: SOA (safe operating area) assessment for power devices requires capturing transient stress events (e.g., short-circuit, startup) that occur over a few cycles. Oscilloscopes with sufficient bandwidth and single-shot capture capability can measure the voltage, current, pulse width, and timing needed to evaluate SOA.
97. How to measure jitter components with an oscilloscope?
Answer: Deterministic jitter can be measured by recording edge time variation and converting timing spread to UI p-p jitter. Use dedicated jitter-analysis tools and histograms for more detailed separation of jitter components.
98. How to differentiate analog bandwidth and digital real-time bandwidth?
Answer: Analog bandwidth is a fixed front-end specification. Digital real-time bandwidth refers to the highest bandwidth achievable in real-time single-shot operation considering A/D rates and reconstruction factors. Manufacturers often quote analog bandwidth; digital real-time bandwidth may be lower. For single-shot measurements refer to the real-time bandwidth specification.
99. Can an oscilloscope be used as a digitizer?
Answer: Many fast scopes share architecture with digitizers and provide adequate resolution (commonly 8-bit). However, scopes are typically not designed for continuous, high-throughput streaming to disk; dedicated digitizers/data recorders provide higher sustained throughput and direct-to-disk storage for long-duration captures.
100. What is a mixed or combined oscilloscope?
Answer: A combined oscilloscope integrates analog and digital storage oscilloscope capabilities. It can operate as a DSO with automated measurements and storage and can also provide analog-like infinite persistence and familiar display characteristics, offering bright displays regardless of signal repetition rate.
