Question:

oscillator - Why use capacitors with crystals?
• Whenever I come across crystals used in any of MCU or Processor, whether it be 32.768 kHz responsible for Real Time Clock or 25 MHz crystal required for clocking different interfaces connected with the MCU or processor. There are always two capacitors connected with the Quartz Crystal as shown in the fig.

I have few questions here:

1. What will happen if don't connect capacitors with the crystal?
2. How is the value of these capacitors decided?
3. While checking crystals datasheetI will come across a specification like stability +/-5ppm or +/-10ppm. what is the significance of this term?
4. And what are 2nd overtone and 3 overtone crystals?
Essentially, the load capacitance of the crystal, \$C_L\$, is set equal to the combination of the capacitors you're adding and the shunt capacitance of the crystal, so
$$C_L = \frac{C^2}{2C} + C_{shunt}$$