Recently, as embedded systems have rapidly advanced in performance, miniaturization, and modularization, high-speed digital signal and power systems are operating more closely within a single board.

In this process, issues of signal integrity (SI), power integrity (PI), and electromagnetic interference (EMI) have become areas that are no longer easy to handle as separate items.

In actual debugging situations, there are quite a few cases where the cause cannot be identified even after checking the waveform with an oscilloscope, or where it is not clearly distinguished whether the current phenomenon is an SI problem or a PI problem.

It is a situation where the waveform is abnormal but the cause is not visible, and while there are measurement results, the criteria for judgment are wavering.

For this reason, in recent hardware design and verification, it is becoming increasingly important to move away from interpreting problems solely through time-domain waveforms and instead adopt an approach that seeks to re-read phenomena in the frequency domain.

This is because even phenomena that appear to be the same, such as ringing or noise, can be interpreted differently depending on which frequency band the energy is concentrated in.

Rather than simply looking at the result that the waveform is distorted, a more accurate analysis of the cause is possible by examining the reflection, resonance, and power network response characteristics that generated the waveform together.

Especially in high-speed digital environments, using only waveforms There are many cases that are difficult to judge.

Typically, via stubs or residual stubs in connectors can cause reflection and resonance, distorting the signal.

As Return Loss increases, signal energy is not fully transmitted and returns, degrading the eye diagram and reducing the timing margin.

On the other hand, this phenomenon may appear in the time domain merely as the "waveform being messy."

In this case, frequency domain analysis becomes a tool that more clearly reveals in which bands specific discontinuous structures cause problems.

The situation is similar in terms of power integrity.

Recent devices require higher current at lower voltages, and because of this, the response characteristics of the PDN directly affect system operation.

The instantaneous voltage drop that occurs during load changes, known as Dynamic Voltage Drop, may appear to be a simple voltage fluctuation, but the actual cause may lie in PDN resonance or decoupling design imbalance.

In particular, in environments where multiple signals switch simultaneously, problems that appear to be SI are often actually caused by PI issues.

Conversely, there are cases where discontinuities in the signal path worsen switching current characteristics and manifest as PI problems. Ultimately, the two are not separate items but interconnected issues that influence each other.

EMI is also a prime example of an area where it is difficult to find a solution by looking only inside the PCB.

As systems become smaller and wireless modules are integrated at high densities, internal interference and external radiation issues become more complex.

It is easy to miss the cause if you do not approach it from the perspective of the whole system, including cables, housing, grounding structure, and surrounding module placement.

Even if it appears fine at the board level, radiation characteristics may differ in the actual product state, and internal interference can lead to performance degradation or malfunction.

Therefore, recent EMI response is expanding beyond simple specification compliance to system-level analysis that includes structures.

Ultimately, the important thing is not to first determine whether it is SI or PI.

The more important questions are closer to “through which energy pathway did this phenomenon manifest,” “in which frequency band is the problem prominent,” and “whether changing the signal, power supply, or structure results in the greatest improvement.”

What is required of a hardware engineer is not merely a sense of interpreting waveforms themselves, but an integrated perspective that reads signal paths, power networks, and system structures together based on measurement theory.

If you look at the waveform with an oscilloscope but still can't find the answer, it is time to suspect the frequency components and resonance structure hidden behind the waveform first, rather than the shape of the waveform.

As the boundaries between high-speed digital design, power design, and EMC compliance become increasingly blurred, frequency domain-based debugging is approaching a necessity rather than an option.

Meanwhile, a webinar will be organized to examine the challenges of such hardware debugging in a more structural way.

This webinar Wave Incense CTO Kim Gwi-soo will present on the topic of ' Debugging SI/PI/EMI in the Frequency Domain: Integrated Analysis Strategies for Hardware Engineers ,' covering a practical approach to diagnosing complex hardware problems through frequency domain analysis based on measurement theory.

The key is not merely to interpret time-domain waveforms, but to identify the more fundamental cause of the problem by examining frequency characteristics, resonance, reflection, and power network response characteristics together.

To participate in the webinar, click the webinar guide banner on the right.