Oscilloscope's key indicators analysis - Database & Sql Blog Articles

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Today's fast, complex digital designs require more physical layer analysis than ever before. Choosing the right oscilloscope can help engineers perform measurement analysis directly on the instrument, which can shorten the design verification cycle by several weeks. 80% of engineers worldwide use Tektronix oscilloscopes to speed up the commissioning and testing of their designs. The author of this article, Zhang Tiansheng, Marketing Development Manager of Tektronix Greater China, explained some key indicators of the oscilloscope when interviewed by a well-known media in China, and made a trend forecast at the end.

1. How important is bandwidth to the oscilloscope? Engineers also mention categories, which means that bandwidth is not the only measure. High bandwidth also means more noise. How to deal with this problem?

In fact, oscilloscopes with the same bandwidth will exhibit different rise times because the bandwidth is determined at -3 dB without providing any information about the linearity of the frequency response or phase response. Different amplifier characteristics (filter characteristics) cause the frequency response to drop more or less at high frequencies, causing considerable fluctuations in the available bandwidth of the amplifier. However, for applications, measuring the errors that occur on the rising edge is critical, and in the data signal, the effect on the opening of the eye is also large. For this reason, the rise time indicator is very important for devices (oscilloscopes) that perform measurements in the time domain. With this indicator, users can more easily understand the measurement data.

Noise is not only dependent on bandwidth, but also on the steepness of the drop beyond the band limits. A good balance between linear frequency response, moderate drop, ideal pulse characteristics and noise is required. In our device, you can limit the available bandwidth for a given application and dramatically reduce noise by adjusting the DSP (Digital Signal Processing) bandwidth in the vertical menu.

2. What does maximum storage capacity mean? The current standard does not use the maximum storage capacity, but which applications will be used?

The maximum storage capacity determines the recording time of the oscilloscope. A storage capacity of 250M points and a sampling rate of 100 GS/s (= 10 ps/point) will result in a maximum recording time of 2.5 ms. This time can only be increased by reducing the sampling rate. An oscilloscope that uses DSP frequency response correction technology is not allowed to do so, so the measurement signal may be misunderstood. In our instrument, the DSP can be activated to reduce the sampling rate to the Nyquist frequency (sampling rate > 2 times the input bandwidth); the DSP can also be turned off, and any sampling rate can be selected to significantly increase the recording time.

For jitter measurements, the recording time determines the lower limit of the jitter frequency that is correctly measured. At 50 GS/s and 250 MB, the jitter frequency drops by approximately 600 Hz. For most standards and applications, 30 MB of storage capacity is usually sufficient.

3. What can the ENOB value tell the measurement engineer?

The ENOB value (effective bit) indicates the discretization order of the analog-to-digital conversion of the measured signal. This indicator provides a simple reference for the user to evaluate the oscilloscope's ADC accuracy. The ENOB value includes not only the ADC error, but also the noise, sampling error, jitter, and other sources of error of the input amplifier. The ENOB value is also related to the measured signal frequency and generally decreases as the signal frequency increases, but the full value (8 bits) of the ADC cannot be reached even when the frequency of the signal to be tested is very low.

4. What are the important hardware triggering functions provided by Tektronix measuring instruments?

Our oscilloscopes feature multiple hardware triggering circuits that provide complex time and voltage related triggering in addition to typical edge triggering. Pinpoint triggers can implement up to 1400 trigger combinations, including edge trigger, glitch trigger, width trigger, trip time trigger, timeout trigger, pattern trigger, status trigger, setup time/hold time trigger, window trigger, pattern trigger, status Trigger, timer trigger, event trigger, serial word trigger (64 bit), etc.

For data signals with different encodings, Tektronix also offers dedicated triggering features such as AMI, HDB3, BnZS, CMI, MLT3, I2C, SPI and NRZ. An exception is the 8b/10b dedicated hardware trigger up to 6.25 GBit/s, which allows users to trigger 8b/10b characters, strings, exceptions and coding errors in real time.

5. What are the important software triggering functions provided by the measuring instrument?

We refer to the software triggering function as "search and markup." It is very important for the user to understand that all software triggers are search events in the record memory and cannot be used instead of hardware triggers, because large record gaps will occur, so events will be missed.

On the other hand, multiple events can be marked in memory and listed in a table. Search and tag settings can also be copied into hardware triggers, so these events can be triggered in real time. Our equipment can also use the hardware used as a gating function, increasing the analytical capabilities of the oscilloscope. For example, this can apply a read-write data suite to a found DDR memory signal, display a signal in an eye diagram, or perform a jitter analysis.

6. What is the future direction of the oscilloscope? Please briefly introduce the prospects of oscilloscope development.

The momentum of oscilloscopes to higher bandwidth continues, especially in high-speed communications, broadband RF and other design and production projects increasingly require high-bandwidth, high-precision oscilloscopes. For example, the 100G Ethernet workaround, which uses complex modulation techniques (DP-QPSK), requires four analog inputs and a bandwidth of more than 20 GHz for analysis. In view of these applications, Tektronix recently launched a 33GHz high-precision oscilloscope, followed by a detailed blog post, so stay tuned!

In addition to the internal technology of the instrument, the development and enhancement of the probe also plays a very important role. If you can't tap the signal and point to the device, the oscilloscope with the highest bandwidth is not very useful. Tektronix' full range of probe tips, whether for high bandwidth or for special applications such as current measurement, helps to demonstrate our technical features. In view of this, in many cases, probes make measurements a reality, and probes should be considered a very important part of the entire measurement instrument solution.

Many oscilloscope applications also require dedicated application software to make it easier for users to analyze and evaluate measurement data in an automated manner. Tektronix sees growing demand in this area, especially mid-range products, which can provide performance measurements economically. Tektronix is ​​continuing to develop key applications such as automatic power measurement software, jitter and low- and medium-speed serial bus decoding. Tektronix' new Windows 7 platform-based DPO/MSO5000 series is a good example of how we offer solutions that our customers demand at a price that customers can afford.