Hi this is my first post here.
I have a question to which I have not found a conclusive answer from searching across the internet.
When making a PCB for a circuit that uses a standard MCU like a PIC16F84 or an AVR (AtMega family) running up to a maximum of 20Mhz. What are the best practises for PCB layout of the crystal.
I have seen it said by some that there should not be a ground trace under the crystal while others say there should be. I have done several single sided boards without any problems and I am designing my first double sided board using an AtMega AVR, using a through hole crystal.
I aim to connect the oscillator caps (22pf) directly to the AVR ground pin/decoupling cap. And then connect this ground pin to the overall ground pour. This keeps the oscillator ground, isolated from the overall ground.
Should I:
1. Leave empty space on both the top and bottom layer under the crystal?
2. Leave empty space on top layer under crytal and space on bottom layer as well, but extend the capacitor ground as a guard ring track around the crystal?
3. Do a ground pour on the bottom layer under the crystal and leave space on top layer under crystal?
Should I leave emptyspace on on both layers under the crystal or should I leave a ground pour under the crystal only on the on the bottom layer, ie only but leave a gap under the crystal on the top layer. Or
I am wanting the best possible layout, its not critical, but I would like to have a robust design because. Instead of reinventing the wheel perhaps people who have found the best results could share some advice. Thanks
I have a question to which I have not found a conclusive answer from searching across the internet.
When making a PCB for a circuit that uses a standard MCU like a PIC16F84 or an AVR (AtMega family) running up to a maximum of 20Mhz. What are the best practises for PCB layout of the crystal.
I have seen it said by some that there should not be a ground trace under the crystal while others say there should be. I have done several single sided boards without any problems and I am designing my first double sided board using an AtMega AVR, using a through hole crystal.
I aim to connect the oscillator caps (22pf) directly to the AVR ground pin/decoupling cap. And then connect this ground pin to the overall ground pour. This keeps the oscillator ground, isolated from the overall ground.
Should I:
1. Leave empty space on both the top and bottom layer under the crystal?
2. Leave empty space on top layer under crytal and space on bottom layer as well, but extend the capacitor ground as a guard ring track around the crystal?
3. Do a ground pour on the bottom layer under the crystal and leave space on top layer under crystal?
Should I leave emptyspace on on both layers under the crystal or should I leave a ground pour under the crystal only on the on the bottom layer, ie only but leave a gap under the crystal on the top layer. Or
I am wanting the best possible layout, its not critical, but I would like to have a robust design because. Instead of reinventing the wheel perhaps people who have found the best results could share some advice. Thanks