[Test Case Sharing] SpectrumView cross-domain analysis accelerates EMI diagnosis

background

In analog integrated circuits such as power management chips and isolation chips, various current and voltage changes (i.e., dv/dt nodes and high dI/dt loops) will continue to occur between many circuit components (such as transformers, power tubes, etc.) and on wires, and affected by high-frequency parasitic parameters, these components will continuously generate various electromagnetic waves through electromagnetic induction effects, which are conducted through power lines or radiated externally by antenna effects, affecting normal circuit functions, resulting in equipment performance degradation, communication interruption or failure, and even causing serious interference to the normal operation of other sensitive electronic equipment around, and even causing accidents in serious cases. Analog IC devices such as power management chips are very susceptible to EMI (electromagnetic interference) due to their high sensitivity, system integration, and wiring layout design.

Faster switching speeds and steeper rising edges exacerbate EMI issues.

Testing requirements

Based on safety considerations, industries such as automobiles and medical electronics have strict requirements for electromagnetic interference. Compliance with electromagnetic compatibility (EMC) standards is a very important task for all manufacturers, which is closely related to product development costs and time to market. Taking the new energy vehicle industry as an example, with the introduction of new semiconductor technologies such as silicon carbide, the power is higher than ever before, and there are more high-frequency switching devices. The EMC performance requirements of the components supplied by various suppliers by the OEMs are becoming more and more stringent. In order to ultimately ensure the electromagnetic compatibility of electric vehicles and make the radiated emissions of the whole vehicle meet the standard requirements, the international standard CISPR 25 and the Chinese standard GB/T 18655-2018 stipulate the limit requirements and measurement methods for the conducted emissions of high and low voltage components of electric vehicles in the frequency band of 150kHz to 108MHz and the radiated emissions in the frequency band of 150kHz to 2.5GHz.

However, the cost of EMC certification testing is high and the testing process is cumbersome, often requiring designers to conduct multiple designs, rectifications and tests, resulting in product launch delays. Therefore, it is very necessary for engineers to conduct pre-consistency testing during the design phase to improve product design and ensure that the subsequent products pass the EMC certification.

Test Method

Standard SpectrumView function

The SpectrumView that comes standard with the Tektronix 4/5/6 Series MSO Oscilloscope provides both a decimation filter for the time domain and a digital downconverter for the frequency domain behind each FlexChannel. As shown in the signal acquisition and processing architecture, after the analog signal is converted to a digital signal by the ADC, the time domain and frequency domain are processed in parallel, so that the time domain and frequency domain capture time can be set independently. Therefore, two different acquisition paths can simultaneously observe the time domain view and frequency domain view of the input signal, and provide independent acquisition settings for each domain, just like a spectrum analyzer to discover steady-state and transient RF activities.

Noise spectrum

Unlike spectrum analyzers, the spectrum view of 4/5/6 series MSO oscilloscopes can use any type of probe, measure very low frequency signals, and support multi-channel measurements. The figure above shows the noise spectrum, which supports setting the horizontal axis to logarithmic coordinates. The figure below shows the time domain and frequency domain for simultaneous observation of conducted and radiated noise.

Advanced trigger types

Tektronix 4/5/6 series MSO mixed signal oscilloscopes have the RFVT (RF and time correlation) hardware trigger option. As shown in the figure, the frequency hopping signal is observed after turning on the RF amplitude and time waveform view. It can be intuitively seen that the signal jumps once every 5 milliseconds, skipping three frequencies. The RFVT option supports hardware triggering on the edge, pulse width and timeout events of the waveform to capture anomalies faster. In addition, there are RF frequency, RF phase and time correlation trigger functions.

Interference source location

Using a 4/5/6 series MSO mixed signal oscilloscope with a magnetic field probe or electric field probe, you can locate the noise source and analyze the type of interference source. The spectrum view also supports peak marking, maximum/minimum value hold, and averaging functions, making it easy to conduct comparative tests.

The following figure shows the measurement of the MOSFET turn-on moment using a high-voltage differential probe, a current probe, and a near-field probe. The spectrum changes at the turn-on moment can be observed synchronously in the spectrum view.