rope weaving, webbing furniture, polyester and olefin material make the rope are look natural and more comfortable when you touch on the sofa. rope weaving furniture, webbing furniture Golden Eagle Outdoor Furniture Co., LTD. , https://www.geoutdoor.com
This article explores the long-standing challenge of power supply noise measurement, drawing on extensive practical experience, supported by real-world test cases, and complemented with simulation analysis. When analyzing power supply noise, the traditional method involves using an oscilloscope to observe the waveform and measure its amplitude in the time domain, which helps identify the source of the noise. However, as digital devices operate at lower voltages and higher currents, power supply design has become increasingly complex, necessitating more advanced testing techniques.
To address this, the paper presents a case study where frequency domain analysis is used to investigate power supply noise. When the time-domain waveform is difficult to interpret, Fast Fourier Transform (FFT) is applied to convert the signal into the frequency domain for detailed analysis. This dual approach—examining both time and frequency domains—can significantly speed up the debugging process.
During board-level debugging, it was discovered that the power supply noise reached 80 mV, exceeding the device’s specifications. To ensure stable operation, this noise needed to be reduced. Before proceeding with fault-finding, the principles of power supply noise rejection were reviewed. Different components suppress noise across various frequency bands, including the voltage regulator module (VRM), decoupling capacitors, PCB power-ground planes, chip packages, and the integrated circuit itself.
The VRM typically operates in the DC to low-frequency range (around 100 kHz), while decoupling capacitors cover mid-range frequencies (tens of kHz to hundreds of MHz). Due to parasitic inductance, high-frequency decoupling becomes challenging. PCB power-ground planes act as large capacitors, and chip packages handle high-frequency noise. High-end devices often include on-chip decoupling capacitors, reducing the need for external ones.
In one instance, adding decoupling capacitors only slightly reduced the ripple, indicating the noise might be outside the effective range of those capacitors or that the VRM loop characteristics were affected. To resolve this, the oscilloscope’s frequency domain analysis was employed. Using FFT, the spectral characteristics of the power supply noise were examined, revealing that the main energy was concentrated around 11.3 kHz, suggesting impedance issues in the power distribution network at that frequency.
Further investigation revealed that the VRM's phase margin was below the required 45 degrees, and the crossover frequency was too low, leading to poor noise suppression. By optimizing the VRM loop, the phase margin was increased to 50 degrees, and the crossover frequency was raised to approximately 46 kHz. After optimization, the ripple was reduced to 33 mV, meeting the device requirements.
This example highlights how the oscilloscope’s FFT function can quickly identify and resolve power supply issues. Combining frequency domain analysis with long memory depth allows for efficient examination of low-frequency, long-period signals, making it an invaluable tool in digital circuit debugging.