Oscillators – Page 3
Crystal Oscillator & Advanced Oscillators
Crystal oscillators are used when very high frequency stability is required.
1. Crystal Oscillator
A crystal oscillator uses the piezoelectric effect of quartz crystal.
When voltage is applied:
- Crystal vibrates mechanically
- Mechanical vibration generates electrical signal
Thus the crystal acts like a very high Q resonant circuit.
Equivalent Circuit of Crystal
A quartz crystal is electrically equivalent to:
- Series inductance (L)
- Series capacitance (C)
- Series resistance (R)
- Parallel capacitance Cp
Thus the equivalent circuit contains both series resonance and parallel resonance.
Series Resonant Frequency
At series resonance:
XL = XC
Thus
ωL = 1 / (ωC)
Therefore
fₛ = 1 / (2π √LC)
Parallel Resonant Frequency
Due to parallel capacitance Cp:
fₚ ≈ fₛ √(1 + C/Cp)
Parallel resonance frequency is slightly higher than series frequency.
2. Clapp Oscillator
Clapp oscillator is a modified version of the Colpitts oscillator.
An additional capacitor is added in series with the inductor.
Advantages:
- Better frequency stability
- Reduced transistor parameter effects
Frequency of oscillation:
f = 1 / (2π √(L Ceq))
Where
1/Ceq = 1/C1 + 1/C2 + 1/C3
3. Oscillator Applications
- Radio transmitters
- Signal generators
- Clock circuits in digital systems
- Microprocessor timing circuits
- Communication systems
4. Quick Oscillator Formula Revision
| Oscillator | Frequency |
|---|---|
| RC Phase Shift | f = 1 / (2πRC√6) |
| Wien Bridge | f = 1 / (2πRC) |
| Hartley | f = 1 / (2π√LC) |
| Colpitts | f = 1 / (2π√LC) |
| Crystal | f = 1 / (2π√LC) |
.png)
No comments:
Post a Comment