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ferrit beads, inductors in analog board for noise reduction

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Newbie level 6
Dec 28, 2005
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I have desinged an ultrasonic system. However the singal is very noise. Then I added a couple of ferrite beads on power suppy to the board, It seems work much better. But I wonder if there is any rule on using them. Can I just use ferrit beads as much as possible? I was using inductor with two capacitors (one big, one small) in my power leads to the analog board, but the inductor seems not working at all until I replaced the inductor with the ferrite beads.

I am going to redo my pcb and add ferrit beads, but I would like to get some advice before I make another pcb.

Thank you very much for your advice.

Re: ferrit beads, inductors in analog board for noise reduc

There are some general rules to improve the interference

1.) ic decoupling should connect to ic ' gnd ' pin through shortest path.

2.) Use both big and small cap. e.g 100nF and 10nF

Basically, you can add ferrite beads to any point that helps to improve the circuit performance. However, I personally believe this is not necessary. You only need to find out which part of the circuit has most significant effect.


Can you attached your circuit or block diagram?

Ferrite beads suppress high frequency noise in electronic circuits. They provide attenuation of selected frequency bands.
Their main purpose is to reduce EMI (electromagnetic interference) and RFI (radio-frequency interference)

Re: ferrit beads, inductors in analog board for noise reduc

ferrite bids is suitable for current noise and capacitors is very good for voltage noise. u should see what kind of noise is there in your circuit. if u have 2 circuit with 2 different voltage and want to connect them to each other ferrite bids is suitable but if u have only one capacitors is good.

Re: ferrit beads, inductors in analog board for noise reduc

attached file is the schematic. I am using DXP 2004, which is protel. I have three power coming into the board, +12, +5, -5. HCF4067 is an analog switch for multiplexing. IRF830 is used for generating negative spike. AD604 is used for amplifing the signal. The signal is then sent to a digital board for digitizing.

Re: ferrit beads, inductors in analog board for noise reduc

Read this.


Use quality high frequency bypass caps preferably SMT ceramic (X7R) and Tantulm. If you must use through holes keep lead lengths short and small spacing. You might want to read up on selecting bypass caps too. Improper bypassing can create problems rather then prevent them. Use quality aluminums with smallest lead spacing for low freq bypass . I've had impressive results with "Polymer Aluminum caps" unfourtanetly they only go to 16V. Also any traces that carry high di/dt keep as thick and short as possible,this was the cause of a recent noise problem I had.

Also be sure you are measuring correctly using the ground clip provided with your probe is convenient but it creates a ground loop and adds inductance.Try using the small wire provided with your probe attached directly to your probe tip. Check for ground contamination (bounce) .

For posting a schematic just take a screen capture and upload it to a free image host. I don't have Protel.

Good luck

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