PCB Design advice

Hi,
I am doing a VoIP device using PIC so it will have digital part as well as analogue part (preamp, power amplifier etc).
Besides having lots of grounding between the analog section and digital section, is there any other thing i need to put more attention on..?

I am just worried of the trace being to thin until it limits the audio signal, and also worried of noise in relation to the analog section.

For most part of the PCB board, the trace would be 1mm. Of course the trace for the supply will be more thicker..

In the circuit, there are 2 section where the analog section meets digital section which is the PIC's ADC and PIC's PWM (use as DAC). I am especially worried about these part. Is trace of 1mm enough for the audio signal to flow succesfully? Do I need thicker trace for the analog section..?

One of my friends did am amplifier circuit and because his trace is too thin, the amplifier doesn't actually produce any sound.. Besides, its also my first time doing analog related circuit.

How about the effect of noise..? How to overcome..?

So, yeah.. please do advice..
Thanks..

hi,
Look at this pdf, it has all the info.

A trace of 0.1mm is sufficient for audio signals.

Chances are your friend had a trace so thin it actually had a break in it.

1mm is more than enough - I tend to use 0.25-0.5mm traces for most things that don't carry too much current.

MrNobody said:

How about the effect of noise..? How to overcome..?

Click to expand...

I think the solution to the noise/interference problem is a combination of good track layout and using a ground plane around them to shield them.

That pdf document that eric found is excellent, there do not appear to be many good tutorials like that on the web - at least I have not seen any others yet.

By the way, does anyone know if pcb manufacturers usually charge any extra for cutting shaped pcbs - eg. rounded corners etc?

Thanks alot..
Learn alot of new things..

However, i need some clarification about one statement which is inside the tutorial.

One major example is with mixed digital and analog circuits. Digital and analog just do not mix, and will need to be
physically and electrically separated.

Click to expand...

What does that statement mean..? Does it mean that I need to have seperate board and seperate power (two 9V battery)? 1 board for digital and one board for analog..? How about connection between the analog circuit to the ADC pin of microcontroller and the connection of PWM pin of microcontroller to another analog circuit..? How do I connect them..?

Please advice.. Thanks..

picasm said:

By the way, does anyone know if pcb manufacturers usually charge any extra for cutting shaped pcbs - eg. rounded corners etc?

Click to expand...

The only extra charge is normally the size of a rectangular board. If you have a round board of 5inch diameter you'll be charged a square of 5X5inch.

Boncuk

MrNobody said:

Does it mean that I need to have seperate board and seperate power (two 9V battery)? 1 board for digital and one board for analog..?

Click to expand...

I think it means you should keep the digital and analogue components and their pcb tracks separated from each other on the pcb as much as possible.
Also, you could use separate voltage regulators for each section.

There is a compromise depending on how significant noise interference is in your design. For example, the on-board sound card in my pc motherboard picks up some digital noise, but for most people it is acceptable.

It is possible to have separate digital and analogue ground and supply connection options for some PIC chips with adc inputs such as the 20 pin version of the PIC18f1320, but usually the standard version works ok and they do have the option of using thier built-in voltage reference for better accuracy rather than relying on the 5V supply.


Thanks very much to Boncuk for your advice on pcb shape costs - I will round the corners on my next pcb design.

Thanks alot..

Hi, I am now doing the PCB design..
Regarding the design, the first option I have is doing everything (both Analog circuit and Digital circuit) on one board, which will need a bigger package to contain the board. The second option is to do it in 2 boards (Digital circuit in one board and Analog circuit in another board) and stack the Digital board on top of the analog board (with some gap between the 2 boards). I prefer the second option because it will require a smaller packaging..
Lets say i choose the stacking option, will the analog board at the bottom affect the Digital board at the top or vice versa..? Each board will have its own 5V voltage regulator and its own Ground. Both board will share the same 9V supply tho..

Please advice..
Thanks..

Stacking is fine. I would recommend using double-layer boards for both boards, and making the bottom layer on both boards a ground plane. That should fix any noise problem you might have. Make sure not to have any "ground loops" (that means connect the grounds of the two boards only at a single point).

Thanks..
I'm only using single sided for now as i've completed the designing of layout.. I'll use double sided for next one..
Yeah, I only have one common GND point for both of the board which is for the 9V supply.
Anyway, just out of interest, what is the effect of ground loops..?