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Power Supply Noise reduction techniques Basics and Types

This article covers Power Supply Noise reduction techniques basics and mentions types of Power Supply Noise reduction techniques.

Power Supply Noise Sources

Following are the common power supply noise sources in the PCB circuit.
•Location, width and length of power supply traces and ground traces on the board.
•Multi-stage EMI filters are not used for AC and DC supply portions on the board.
•Bypassing and decoupling capacitors are not used at appropriate places on the PCB circuit which is interfaced with the power supply lines.
•Use of improper earth coupling and grounding techniques on the board.

Power Supply Noise Reduction Techniques

Power Supply Noise Reduction bypassing, decoupling

Following are the most common power supply noise reduction techniques.
➨Use of bypass capacitor to reduce noise current on the power supply lines. Bypass high derivative sinks and sources with appropriate capacitors as per desired frequencies. Avoid formed lead capacitors. Ceramic capacitors are good for high frequencies.
➨Use of decoupling to isolate two circuits on common line. It is used to prevent transmission of noise from one circuit to the other circuit. The common decoupling network is low pass filter. Choose low value and low-Q series inductor in the filter.
➨Increase the mutual coupling between the paths. This is achieved by increasing the width and decreasing the distance between them. Place forward path and return path as close as possible.
➨In two layer boards, use power grid with ground plane. This reduces self inductance. This is applied to digital board design. In analog board, appropriate Cdec tree structure is used to minimize length and inductance.
➨Identify high derivative current sources and sinks and their return paths. All these need to be bypassed. For the total board, 10 mA/µS is ideal limit for max. di/dt.
➨During PCB layout design, place forward path as close to the return path as possible. Maximize trace width to minimize inductance. Avoid long supply traces and layout supply busses in grid or plane.
➨Bypass capacitors are used at appropriate places in feed forward amplifier circuit. Op-Amps are quite sensitive to noise on power supply. Hence op-amp circuit should be appropriately designed to reduce the effect of noise.
➨Use multistage EMI filters to reduce power supply noise to the PCB circuit design. Also refer Noise reduction techniques in device and board design>>.



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