Crystal oscillator

Thread Starter

cesare.magno

Joined May 19, 2021
18
Hello everybody. I want to create a oscillate colpitts with crystal. When I go to read the quartz datasheet, I don't know what shunt capacitance and load capacitance are. Can someone help me?
 

Delta Prime

Joined Nov 15, 2019
1,014
Hello there, welcome to AAC!
:) Most crystal oscillator circuits take on the name of their inventors: Butler, Clapp, Colpitts, Hartley, Meacham, Miller, Seiler, and Pierce, many of these circuits are derivatives of one another.
The Colpitts oscillator uses a parallel resonant tuned circuit. The amplifier is an emitter-follower.
Feedback is provided via a tapped capacitor voltage divider.
Shunt capacitance C0 is
typically listed as a maximum value, not an absolute value.
Shunt capacitance can be measured with a capacitance meter at a frequency much less than the fundamental frequency.
Parallel resonance means that a small capacitance, called load capacitance (CL) should be placed across the crystal terminals to obtain the desired operating frequency. If you have a circuit schematic that would be wonderful! Because obviously knowing the frequency would be of great assistance and then we could tie in the necessary equations for proper oscillation.
 
Last edited:

Ian0

Joined Aug 7, 2020
2,220
Pierce is a good circuit to use for a crystal oscillator (it's the one you find built into microcontrollers).
Place twice the recommended load capacitance from either side of the crystal to ground. (So you have two capacitors in series across the crystal)
 
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