Oscillator

Piersce Crystal Oscillator

• Thw colpitt's oscillator can be modified by by using the crystal to behave as an inductor. The circuit is called Pierce Crystal Oscillator.
• The crystal behaves as an inductor for a frequency slightly higher than the series resonance frequency Fs
• The two capacitors C1,C2 required in the tank circuit along with a crystal as an inductor are used, as htey are used in Colpitt's oscillator.
• As only inductor gets replaced by the crystal, which behaves as an inductor, the basic working principle of pierce crystal oscillator is same as that of colpitt's oscillator

The practical transistoriced pierce crystal oscillator


• The resistances R1,R2,Re provide d.c bias while the capacitor Ce is emitter bypass capacitor. RFC (Radio Frequency Choke) provides isolation between a.c and d.c operation. Cc1 and Cc2 are the coupling capacitor.
• The resulting circuit frequency is the set by the deries resonant frequency of the crystal.
• Change in the supply voltage, temparature, transistor parameters have no effect on the circuit operating conditions and hence good frequecy stability is obtained.