I'm a software engineering student and an electronics hobbyist, and I am currently designing a circuit using a 80Mhz pic32. I wondering if the noise filtering that I have is acceptable and if it could be improved.
The data sheet says that you can optionally have an inductor(ferrite bead?) between the Vdd and AVdd, would this be a good idea? I will be using the adc for measuring temperatures.
"optionally have an inductor . . or ferrite bead" Sounds like the voice of experience in their recommendation.
Make sure you add bypass capacitors on the Analog side of the ferite bead, or the bead won't help. The ferrite bead acts as a high frequency resistor. The higher the frequency the higher the resistance. But doesn't interfere with your supplying the DC required for the Analog supply.
EDIT : I just noticed your 10K resistor from Digital supply to Analog Supply. Using a resistor there is not a good idea, unless you have some reason for the resistor. A resistor will drop voltage at DC (supply to your Analog). A ferrite bead won't cause voltage drop at DC (which is good).
I doubt an inductor or ferrite will be worth it in your situation. I use the pic32 a bit, have never needed to use one. For a 12 bit device, it could be necessary, but for a 10 bit adc, its not going to make much difference. It is quite important to properly bypass the avdd with a 0.1uf, and use a proper pcb grounding scheme.
You haven't said what type of temperature sensor you are using. You can do the math yourself, but the 1.7uf + 10K low pass filter could be simplified to a single cap and resistor. Since the recommended source impedance to the adc is around 1k, it would be better to use a 1k and 0.1uf to 1uf, although the cap relaxes this requirement to a certain degree depending on your sampling rate.
The 0.1 to 1 uf guideline isn't set in stone, its what I tend to do in my projects, and if you use a standard size footprint, you can experiment with different values for best results.
