About PCB layout
In the design of PCB layout, it must "(1) to prevent the reduction of negative resistance", "(2) to prevent EMI problems."
Oscillation circuit pattern length
The oscillator circuit signal pattern length should be as short as possible to minimize stray capacitance / inductance. Jack should not be used in an oscillation circuit, otherwise it will cause a lot of EMI.
Influence around the oscillator circuit pattern
A ground signal path or not in the middle layer of a multilayer circuit board, and thus overlaps with the oscillation circuit, as a result, stray capacitance between the ground and the oscillator circuit will increase.
Stray capacitance increases may result in insufficient oscillation margin, resulting in oscillation stops. Signal path close to C-MOS inverter input waveform due to amplification noise generated EMI.
Electrically shielded by the ground pattern
If you schedule a grounded electrical shielding region, to be placed in the back of the oscillator circuit board. The ground pattern placed in the middle layer, the oscillation margin will appear above. Around the oscillation circuit ground pattern should be close to the oscillation circuit, to prevent a large stray capacitance.