Practical Electronics/Generators/Oscillators

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An oscillator is a circuit which generates a repetitive electric signal of given waveform (for example a sinewave).

Electronic Oscillation[edit]

Electronic Oscillator is an electronics circuit that generates oscillation when circuit is in resonance a natural process when all the frequency components cancel out . Commonly found in LC and RC Phase Shift

In electronics, oscillation occurs when the following conditions are met

  • Output voltage is equal to input voltage and inverted
  • The Phase Angle difference between input and output voltage must be 180

Passive Oscillation[edit]

With Series LC or Parallel LC . At Resonance, the frequency dependent components will cancel out ie impedance of inductor will cancel impedance of capacitor Z_L + Z_C = 0

Z_L = Z_C
\omega L = \frac{1}{\omega C}

Solving for ω

\omega = \sqrt{\frac{1}{LC}}

Since ω = 2πf therefore

f = 1/2π \sqrt{\frac{1}{LC}}

This frequency is called Resonance Frequency and usually denoted as fo

At Resonance Frequency

V_L = Z_C or V_L - Z_C = 0 or V_C = - Z_L

The voltage of the series LC keeps oscillating between inductor's voltage and capacitor's voltage between phase angle 0 - 180

In LC circuit, oscillation occurs at the resonance frequency
f = 1/2π \sqrt{\frac{1}{LC}}

Active Oscillation[edit]

Fixed Frequency Oscialltor[edit]

For active cicuit, to meet the requirement for oscillation require

An Inverter that has output voltage equals to input voltage and inverted . So any Transistor or Op Amp Amplifier can be configured to act as an Inverter
A Feedback circuit between input and output that provides 180 degree difference in phase angle . This can be achieved through Resonant Tuned LC circuit or three stage of RC Phase Shift with each stage has a phase shift of 60

For Resonant Tuned LC circuit, the oscialltion frequency is equal to the resonant frequency

fo = 1/2π \sqrt{\frac{1}{LC}}

When choosing the value of  \sqrt{\frac{1}{LC}} in power of 10 so that  \sqrt{\frac{1}{LC}} is equivalent to 10-½n then the oscillating frequency can be calculated by

fo = 0.3 x 10-½n

For RC Phase Shift

Tanθ = 1/2π f \frac{1}{RC}
Tan 60 = Sin 60 / Cos 60 = \frac{\frac{\sqrt{3}}{2}} {\frac{1}{2}} = \sqrt{3}

Therefore the frequency change through phase change is

f = 1/2π \sqrt{3} \frac{1}{RC}

When choosing the value of \frac{1}{CR} in power of 10 so that \frac{1}{CR} is equivalent to 10-n then the oscillating frequency can be calculated by

fo = 0.33 x 10-n

Variable Frequency Oscialltor[edit]

Variable Frequency Oscialltor can be achieved through inverter with feedback circuit of

  • 2 series inductors L1 + L2 in parallel to one capacitor C
fo = 1/2π \sqrt{\frac{1}{(L_1 + L_2)C}}
  • 2 series capacitors C1 + C2 in parallel to one inductor L
fo = 1/2π \sqrt{\frac{1}{(C_1 + C_2)L}}
  • 2 series capacitors C1 + C2 in parallel to a tuned LC

Electro-Mechanical Oscillation[edit]

Crystal Oscillator[edit]

A crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency.

fo = n fc