Hey guys,
I am wondering what is the proper way of isolating ICs, Sensors, and Modules from interfering with one another on the same PCB? Power interference that is.
For example, I have a circuit board with a microcontroller, an RF module, and some sensors onboard. The RF works great with the sensors removed from the board... but as soon as the sensors are soldered in the RF barely works. The RF is very sensitive to noise on the power rail. The sensors must be introducing noise into the power some how. Up until now, I have only just used decoupling capacitors on everything, but this doesn't seem to cut it?

I'm wondering if there is a good practice to follow for this stuff in general? I have read up on how you can use a ferrite bead/inductor and some capacitors between parts, but I am looking for a bit more information on this. How do you decide on a decent inductor/ferrite bead for this? Do you put this filter inbetween every single sensor/module on the board and the power interference should be minimal?

Here is an image I came across:

Is there a good general ferrite/inductor and capacitors that I could start off with? I don't know where to start as far as values go.

Thanks and any help is greatly appreciated!

 

I just realized... I'm wondering if I should of put this in the Analog & Mixed Signal category.

 

Figured I would check back in on this? Does anyone have any insight on this subject?

 

Figured I would check back in on this? Does anyone have any insight on this subject?

Usually the modules have some suggestions for filtering. do you have a spec sheet you could post?
Anything I would suggest would only be a swag.

 

Usually the modules have some suggestions for filtering. do you have a spec sheet you could post?
Anything I would suggest would only be a swag.

This is the sensor that I am using. No information on a power filter:
http://eng.gassensor.ru/data/files/carbon_dioxide/mh-z14.pdf

 

This is the sensor that I am using. No information on a power filter:
http://eng.gassensor.ru/data/files/carbon_dioxide/mh-z14.pdf

I was thinking about the RF module. But the one you posted might help. Try a 100Uh choke for the inductor.

 

I was thinking about the RF module. But the one you posted might help. Try a 100Uh choke for the inductor.

Are there some typical capacitor values I would use along with the 100uH inductor? The average current says 85mA, and I believe peak current is 200mA. So I would want an inductor rated for say 400mA?

 

Are there some typical capacitor values I would use along with the 100uH inductor? The average current says 85mA, and I believe peak current is 200mA. So I would want an inductor rated for say 400mA?

The 10uF can just be elecrolytic. The .1 should be ceramic.
3 or 400 ma should be good for the inductor.

 

Hey guys,
I am wondering what is the proper way of isolating ICs, Sensors, and Modules from interfering with one another on the same PCB? Power interference that is.
For example, I have a circuit board with a microcontroller, an RF module, and some sensors onboard. The RF works great with the sensors removed from the board... but as soon as the sensors are soldered in the RF barely works. The RF is very sensitive to noise on the power rail. The sensors must be introducing noise into the power some how. Up until now, I have only just used decoupling capacitors on everything, but this doesn't seem to cut it?

I'm wondering if there is a good practice to follow for this stuff in general? I have read up on how you can use a ferrite bead/inductor and some capacitors between parts, but I am looking for a bit more information on this. How do you decide on a decent inductor/ferrite bead for this? Do you put this filter inbetween every single sensor/module on the board and the power interference should be minimal?

Here is an image I came across:

Is there a good general ferrite/inductor and capacitors that I could start off with? I don't know where to start as far as values go.

Thanks and any help is greatly appreciated!

Most of the attention should go to the print layout. coil (uH depending on freq spectrum) and cap's and their grounding points are also important
a: no other currents in the analog layers then the ones you need there.
b: no long tracks or windings/ loop in the tracks
c: central power and gnd connection point between ana and digital.
d: no overlapping planes hence pcb act as a capacitor ( between the layers)
when a mixed chip is used ( like mcp 355x series) care should be taken at the central GND point hence its used by dig and analog.
eq at a 22bit adc you talk about nano volts per bit at a track resistance of 1mOhm and a current of 100uA could produce problems.
Without all information provided is a simple answer not possible.
Picbuster

 

Don't overlook point c. above, it is the best advice here.

Do not think of ground or busses as zero resistance wires. Think of them as resistors and series inductors. When you connect them together you want to make that connection at the cleanest points possible.

That is the output of the power supply itself. The worst offenders are typically the noisy digital things interacting with the analog things. Let the grounds connect at one point as close to the power supply as possible, so noise goes back to the supply and not thru other wires.

I had a PCB no larger than a postage stamp, micro computer one side and high gain op amp the other. It required a respin to move one ground trace from the micro directly to the filter cap where it met the trace to the analog side. Then all was well with a 3MHz 60 dB amp not getting interfearance from the micro clocking at 4 MHz.