Printed Circuitboard (PCB) layout tips?

[Paul Victorey]

OK, I'm having some custom PCBs manufactured, so I was looking for any general layout tips. This would be for a combination of analog & digital circuitry, so I know that I should have an analog and a digital ground, which only connect at one point. I also know that I should never have ground loops, but rather use a "star" or "bus" topology for the ground traces.

This doesn't have any tricky constraints, so I don't need the very application-specific design tweaks like some applications, but I'm looking for tips on how to make a good PCB, in general.

If you need to know a little about the application, it's a control system:

The basic analog circuitry consists of a variable-resistance sensor in a wheatstone bridge, connected to an op amp (which is set up as a somewhat modified differential amplifier), and passed through a low-pass RC filter, into an ADC; I also know that the capacitor of the LP-filter should be very close to the input of the ADC, to reduce noise on the ADC input.

The ADC output goes to a microcontroller which has been programmed and tested; the digital circuit basically periodically polls the ADC for the current sensor reading and makes the appropriate decisions.

So, what are the pitfalls, the tricks of the trade, etc. for laying out a PCB? Now that everything is final and working, it seems the next step for the prototype.

I'd suppose the single common point of the analog and digital grounds should be where the power supply connector ground is attached to the PCB.