Technical questions and answers on debugging and verifying circuits with fluorescent oscilloscopes

Q1: How can we test the signal quality of 100M Ethernet and Gigabit Ethernet easily? How many desktop devices can we recommend? How many portable devices can we recommend?

A1: The Ethernet physical layer signal quality test can use the industry-wide widely used solution provided by Tektronix.

Q2: How to perform power supply test?

A2: Tektronix provides a full set of power supply test solutions, including various current probes, voltage probes, and analysis software. The testable current amplitude ranges from 1mA to 20KA, and the bandwidth ranges from DC to 2GHz; the testable voltage amplitude ranges from 1mV to 40KV, and the bandwidth ranges from DC to 1GHz (low voltage can reach 16GHz), which is the widest range in the industry. The testable items include: switching loss and safe working area of ​​switching devices; inductance, magnetic loss, BH curve, conductivity of magnetic components; ripple, power factor, current harmonic analysis of power supply, etc. Many of these test items are only provided by Tektronix.

Q3: How does the oscilloscope's storage depth affect signal testing?

A3: The memory depth will affect the test window and test items of the oscilloscope. For example, a traditional oscilloscope with a sampling rate of 20GS/s and a maximum memory depth of 1M or a sampling rate of 40GS/s and a maximum memory depth of 2M can only collect 50us signals.

Q4: Please give an example of the application of digital phosphor oscilloscope in automotive electronics design and debugging.

A4: The digital phosphor oscilloscope provides timing and protocol decoding analysis functions for CAN bus and LIN bus. It can synchronously decode control networks with CAN and LIN buses to test transmission accuracy and error tolerance between networks. Network synchronization faults can be located by testing crystal tolerance and transmission delay. Fault debugging on the data link layer is achieved through the integrated search function. Through the eye diagram test of the CAN signal, the noise on the CAN data packet caused by jitter, amplitude distortion and burrs can be analyzed. Complex trigger conditions can be used: frame type (data, remote, error, overload), identifier, data, confirmation loss and bit stuffing error to trigger the acquisition of positioning signal characteristics and faults.

Q5: Can a digital oscilloscope directly measure AC220 mains power? How to measure mains power?

A5: You can choose a high voltage probe.

Q6: How should we define the trigger signal required by the user?

A6: It is recommended to use the DPO function to find the specific parameters of the signal we want to trigger, such as amplitude, time and other information.

Q7: The Cass-D amplifier outputs through an inductor. I want to test the output waveform. How do I connect the oscilloscope probe?

A7: Just connect the oscilloscope probe to the inductor.

Q8: Can the jitter parameters be set? For example, time and number of times?

A8: When testing jitter, you can change the number of test samples (that is, the test time/number of times).

Q9: What are the functions of Tektronix's digital phosphor oscilloscope? What is the difference between this oscilloscope and a traditional oscilloscope?

A9: The biggest difference is that it greatly improves the waveform capture rate, which is different from the refresh rate. It can help us fundamentally improve the probability of capturing occasional failures. Another difference is the improvement in display performance.

Q10: If I want to capture a 20MHz RF signal, a sinusoidal signal, does my oscilloscope need a bandwidth of 1GHz?

A10: If it is a sinusoidal signal, then 1G is not necessary. In addition, the required bandwidth is related to our test accuracy requirements. [page]

Q11: How to debug DDR or DDR2 SDRAM?

A11: For DDR and DDRII signals, since there is no standard for the signals themselves, accurate testing should be performed based on the requirements of different DDR/DDRII chips, including the voltage/timing relationship of the signals.

Q12: What is the biggest advantage of DPO? What are the key points to pay attention to when selecting a model?

A12: The biggest advantage is the very high waveform capture rate, which can help us find occasional faults and help us accumulate enough test samples in a very short time.

Q13: How to test PSRR with an oscilloscope?

A13: The ratio of the percentage change of full-scale voltage to the percentage change of power supply voltage is usually called power supply rejection ratio. The power supply rejection ratio can be divided into AC power supply rejection ratio and DC power supply rejection ratio.

Q14: What is the difference between a digital oscilloscope and a fluorescent oscilloscope?

A14: The digital phosphor oscilloscope is a third-generation oscilloscope innovatively designed based on the digital storage oscilloscope. It greatly improves the waveform capture rate and has significant improvements in triggering/bandwidth/performance.

Q15: How to solve the grounding problem of the probe when measuring high frequency? Is it enough to just connect the probe ground to the oscilloscope probe ground?

A15: The probe ground must also be connected to the DUT ground to ensure that the test system and DUT share a common ground.

Q16: When debugging high-frequency circuits, is there any good solution to reduce the trouble caused by the parasitic inductance of the oscilloscope probe?

A16: The first thing is to choose a suitable probe; the second is to keep the ground wire as short as possible and the ground signal as close to the detection signal as possible. The loop formed between the ground wire and the measured signal should be the shortest.

Q17: When the amplitude of the detected signal changes regularly between 2.5-10mV, the frequency is 70.7MHz. The bandwidth of the oscilloscope is 500M. How to distinguish the effective signal from the noise of the oscilloscope?

A17: You can use a termination to terminate the oscilloscope channel to 50 ohms. Test the noise of the oscilloscope itself first. Or consult the oscilloscope manual, so that when you test the actual signal, you will have a clear idea of ​​the impact of the oscilloscope noise on your signal.

Q18: If the test signal is difficult to measure during the test, such as inside the cabinet, and only flying wires can be used, how can the impact of this measurement be reduced?

A18: Use good flying leads, and keep the signal line and ground line as close as possible to ensure good coupling. Also, keep them as short as possible.

Q19: What is the format of the stored files?

A19: As needed, the oscilloscope can store a variety of content such as waveform data, pictures, and settings. The file format can be binary, text, CSV, and special file formats that can be recognized by tools such as Mablab.

Q20: What are the main indicators to consider when purchasing an oscilloscope?

A20: When choosing an oscilloscope, you need to consider the oscilloscope's bandwidth, sampling rate, storage depth, number of channels, analysis capabilities, probes and other indicators and related factors based on the frequency, amplitude, type and number of channels of the signal to be tested. Due to space constraints, we cannot list them all here. You can request the "Digital Phosphor Oscilloscope Selection Guide", which contains detailed descriptions of related issues.

Q21: How many logic analyzer channels does the oscilloscope have?

A21: MSO mixed signal oscilloscope in the digital phosphor oscilloscope family, with 16 digital channels. Ordinary oscilloscopes do not have digital channels, but you can use the iLink toolset to integrate any Tektronix oscilloscope with any Tektronix digital phosphor oscilloscope to form a time domain-logic domain comprehensive test system.

Q22: We have a TDS2024B oscilloscope, but when it is connected to the computer through Ni's software, the waveform is delayed. How can we solve this problem?

A22: Transmission delay is inevitable. You can try to use a faster connection to reduce the delay.

Q23: How to choose an oscilloscope based on the data rate to test the eye diagram, etc. For example, 5Gbps

A23: The base frequency of a 5Gbps signal is half of the data rate, i.e. 2.5GHz. To verify a signal of this rate, it is generally necessary to collect the fifth harmonic, i.e. a 12.5GHz oscilloscope. If debugging is required, the bandwidth requirement can be slightly reduced.