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
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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