Quartz crystal oscillators, one of the finest and cheapest ways to keep track of time in a stable manner without a network connection. The typical circuit connects a crystal and two capacitors to an integrated circuit. As explained in a previous blog article, inside the integrated circuit is a “clock generator” circuit which is basically an inverting amplifier connected to the two pins of the crystal oscillator circuit.
But, how do you determine the capacitor values that you need to use for your crystal oscillator? Here’s how. Look for the “load capacitance” specification in your crystal’s datasheet. You must pick two capacitor values that satisfy the following formula:
C_L = load capacitance of crystal
C_p = parasitic capacitance
C_1 = first capacitor
C_2 = second capacitor
C_L = 1/(1/C_1 + 1/C_2) + C_p
But, what is the parasitic capacitance? It is the capacitance caused due to fat traces, long traces, pins, leads, etc. Generally, using a value around 3-5 pF works well, obviously if you have less ideal wire connections, you should use correspondingly larger values.