Based EMI Digital Oscilloscope pretest

- Aug 02, 2016-

With the development of modern electronic technology, the integration of a variety of electronic devices is increasing. The introduction of a large number of high-speed bus and RF functions, so that the device itself generates more electromagnetic radiation. At the same time, since the user of the electromagnetic compatibility of products have become increasingly demanding procurement, product design, product design engineers must strive to reduce electromagnetic interference (EMI). Various manufacturers have invested a lot of products for EMC compliance testing and certification.

For a typical EMC design and certification process it can generally be divided into three stages, namely, product design, pre-tested (Pre-test), product pre-certification (Pre-compliance) and product certification (compliance test) phase. Product certification involves rigorous standards and test equipment and site requirements, many companies at this stage is done by specialized laboratories of third parties, within the company only pre-tested and pre-certification. The traditional design process after the completion of product design, product testing department to pre-certification. If problems are detected, return the product design department will make appropriate corrective. But because this corrective often need to adjust the design of the circuit, even involving PCB adjustments generally process is complex, time lengthy and costly. Designers hope early in the circuit design will be able to identify problems and timely correction, in order to avoid a large number of rectification work in the future. But a problem we have to face is that EMC equipment is generally expensive, with professional EMC test equipment investment is high for each design department. In addition there is another emerging issue, along with a burst of high-speed bus communications and applications, some of EMI issues are no longer continue to produce the phenomenon, it usually produces a burst communication interval and rate. The limited capacity of traditional EMI receivers capture these issues. More importantly, instantly we discovered the existence of such intermittent at a certain frequency EMI problems can not provide sufficient information for the designers to diagnose the causes.


When faced with these problems, engineers will think of the most common debugging tool - the oscilloscope, if the oscilloscope can provide EMI test capabilities, will greatly reduce overall design costs. If you can provide some diagnostic information generated EMI reason, engineers design and rectification process will be significantly accelerated.


Regrettably, however, the current market, the vast majority of this work can not be qualified oscilloscope. Although almost all of the oscilloscope have FFT spectrum analysis function, but this function is often poor accuracy, update rate is low, can not be set flexibly, can not reach the pre-EMI testing requirements.


Insufficient oscilloscope FFT function has the following main reasons: First, the lack of dynamic range. Oscilloscope A / D is generally eight, but the number of bits (ENOB) can actually be used effectively often inadequate 6, in this case can not accurately measure the tiny radio frequency signal. Plus a lot of noise analog front end, making the oscilloscope's dynamic range is only about 40 ~ 60dB. Rohde & Schwarz (R & S) has the full bandwidth of the oscilloscope RTO> 7bit the ENOB, RF instrumentation with analog front-end level, the noise only 100uv less. This ensures that the RTO oscilloscope can provide more than similar products of 15 ~ 20dB dynamic range.


Secondly, the algorithms and functions implementation issues. No ordinary oscilloscope and spectrum analyzer similar to the down-conversion circuit, and can not set the center frequency analysis range, RBW there is no way to adjust, we can see the spectrum is basically illustrative. If you increase the involvement sample point FFT computation, will greatly reduce the frequency spectrum update speed. R & S RTO oscilloscope FFT function is implemented in hardware. Via a dedicated digital down converter, users can set the center frequency the same as any other spectrum analyzer, the scope of analysis and RBW. Implemented by hardware FFT operation fast and accurate, regardless of other functions and settings, even open a variety of measurement analysis functions, spectrum update rate remained unchanged. Migrating from real-time spectrum analyzer over multiple overlapping FFT algorithm, it can be observed similar devices will not see the side information, greatly reducing the leakage waveform. Another important feature of the RTO oscilloscope spectrum analysis is to analyze the speed and timeliness. Fast spectrum update ensures that the EMI problem of incidental capture and display. Any electromagnetic radiation circuit occurs will not escape RTO oscilloscope FFT function. With the unique frequency mask triggering and MSO function, the user can set a trigger condition EMI, that is, within a certain period or frequency, as long as there EMI signal, the oscilloscope can trigger and capture. In this case not only see the EMI signal itself, with the time-domain signal circuit is connected to the other analog and digital channels, we can analyze what is the cause of the occurrence of the EMI incident. Such as high-speed USB data transfer interface, wake-up work status 2.4GHz RF module.


EMI receiver and complete similar work is the use of an oscilloscope is an important object of the EMI pre-tested. RTO oscilloscope can provide similar test and EMI receiver interface. By MASK test function, we can set a standard template comply with EN whether the observation of the entire system state to meet EMI emission standards. As reference standard for information technology equipment EN55015Q EU tested products from 9kHz ~ 30MHz electromagnetic radiation testing.


Observation is a necessary tool EMI EMI probe and preamplifier. R & S company has a full field magnetic field probe, user-friendly for detecting chip, EMI problems circuits and interfaces. External pre-amplifier bandwidth of up to 3GHz, helping users to capture tiny EMI signals.


The oscilloscope is an electronics engineer most commonly used tools, if they do EMI pre-test work, the oscilloscope must meet high dynamic range, low stray, high waveform capture rate and high-speed FFT computing power requirements. By using the template function test, engineers can also verify the relevant standards and sporadic EMI diagnosis. R & S's RTO oscilloscope set the company many years of RF experience communications and digital design in a particular experience EMC testing using a dedicated ASIC circuit, with strong EMI testing and diagnostic capabilities, it is a powerful tool for electronic engineers.


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