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first pcb steps - sallen key filter

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denver56

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Hi people ! This is my first job in PCB design. WHat you thing about this schematic / board ? The circuits rapresent a sallen key filter.
Thank you allView attachment try.zip
 

Re: first pcb stebs - sallen key filter

Can you pass a jpeg file of this design? I am not able to open your files.
 
Re: first pcb stebs - sallen key filter

here you are =)

 

Re: first pcb stebs - sallen key filter

If this board is 2 layers only then you should place a GND polygon in this way that it should be around signals or use one layer as a GND only and put all signals on the second one. Making GND polygon will give you less noise and less signal reflections because the line impedance will be more constant. Additional plus for the polygon is less EMC noise emitted by the device. You should calculate the PCB track impedance to match it to source impedance. "Saturn PCB" is good and free software for this kind of calculations. Try not us as less vias as possible on signal lines. If this will be very high frequency signals then don't place track in 90 degrees angle. 45 degrees or round are better. The same rule should be for via bottom and top tracks. Hi frequency for analogue signals is larger than 100MHz.
 
Re: first pcb stebs - sallen key filter

The PCB layout is terrible. You should place components so as to minimise track lengths. It has been autorouted which I wouldn't recommend if you have not yet learnt how to do manual routing. I wouldn't autoroute analogue circuitry anyway.

Keith
 
Re: first pcb stebs - sallen key filter

ok I am routing by myself considering only one layer. But for example, how can link C7 avoiding the cross between the link (look at the picture)
Thank you all !!!!!
 

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Re: first pcb stebs - sallen key filter

In this case you must to place pads and later solder a wire for connecting those lines. If it will be short then you can use bottom layer but you should leave the GND polygon as full as possible.

The track between IC1 and C7 has 305 degrees!
 
Re: first pcb stebs - sallen key filter

thank you! could you tell me the specific name of a pad so can i look for it in the EAGLE library ? Thank you !
 

Re: first pcb stebs - sallen key filter

I am familiar only with altium desginer. I am sorry but this time somebody else maybe will help you.
 

Re: first pcb stebs - sallen key filter

ok but what is exactly the role of a pad ? It transport "magically" a wire from a location to another (utilizing the second layer, I guess) , right ?
 

Re: first pcb stebs - sallen key filter

Pad is a PCB element similar to via. Generally on your PCB capacitors' footprints are made from two trough hole pads and a drawing on screen printing layer. This through hole pad allows you to put a wire inside it and solder so this wire will be connected to your track with given signal and you can solder other side of the wire to different pad. This will create a connection between two places on your PCB by the wire.
 

Re: first pcb stebs - sallen key filter

so adding pad in this way is ok ?

 

Re: first pcb stebs - sallen key filter

It's not clear if the available PCB technology allows for dual layer and if through-plated vias are available at all.

I agree with most comments about the present layout except what's said about impedance matching an signal reflections. These things are meaningless for a circuit with 5.5 MHz OPs. Although you didn't mention filter frequencies, it's pretty clear that it's no high speed circuit.

Circuit ground should be designed at least as a meshed net, power supply bypass capacitors near the OPs should be provided as well.

It's reasonable to place the filter components grouped according to the signal flow.

As you are using conventional capacitors and resistors, there's a fair chance to route the circuit as single sided PCB. It would be easier to use DIL OP packages.

P.S.: Seeing your latest post, did you actually decide about SMD versus conventional parts?
 

Re: first pcb stebs - sallen key filter

I MUST use smd component. Are not these smd ?? They told me ,in an another forum, that R-EU_R0805 (the ones that I am using) are smd... Can you tell me the name of a SMD resistor / capacitor component to look for in the eagle library ? Thank you !
 

Re: first pcb stebs - sallen key filter

I would like to clarify about impedance matching and signal reflections. I mean that this applies to the frequency above 100MHz. I apologize for the inaccuracy.

0805 is SMD. As well 0603 etc.
 

Re: first pcb stebs - sallen key filter

so the ones that I am actually using are smd... why did you say that "As you are using conventional capacitors and resistors" ?
 

Re: first pcb stebs - sallen key filter

denver56 said:
so the ones that I am actually using are smd... why did you say that "As you are using conventional capacitors and resistors" ?
Click to expand...

Because your earlier posts show through hole passives!

Keith.
 

Re: first pcb stebs - sallen key filter

Prof. told me to use capacitor sms 0405 but I can't find them in Eagle. Did you have any ide where to find them ? Thx
 

Re: first pcb stebs - sallen key filter

Sounds like a mistake. Common sizes are 1206, 0805, 0603, 0402. There is an 0405 but it is very uncommon. **broken link removed**

Keith.
 

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