ELEX Oscillators

• It is a circuit that produces a periodic waveform on its output with only dc supply voltage as an input. Oscillator
• Oscillator has small power level.
• The phase shift around the feedback loop must be effectively 0 degree or 360 degrees
• The voltage gain around the closed loop gain feedback loop must equal to 1
• It is the frequency determining network. Beta
• To start the oscillation, the loop gain must be less than 1
• To sustain the oscillation, the loop gain must be equal to 1
• Loop gain < 1 Damping
• Loop gain greater than 1 Clipping
• Loop gain equals to 1 Steady oscillation
• It refers to the ability of the oscillator to maintain a constant amplitude in the output waveform. Amplitude stability
• It refers to the ability of the oscillator to maintain its operating frequency. Frequency stability
• No load = infinite ohms
• Full load = 0 ohm
• Components of Oscillator. Amplifier, tank circuit, regenerative feedback
• It boosts the lost or attenuated signal. Amplifier
• A parallel RC circuit that is capable of producing AC signals. Tank circuit
• It provides a path from output to input. Regenerative feedback
• The output of a tank circuit is Sine wave
• It is a device that produces a sine wave output signal. Sinusoidal oscillators
• The output of a sinusoidal oscillator should be constant in amplitude and frequency.
• Types of sinusoidal oscillators. RC oscillator, LC oscillator, Crystal-controlled oscillator
• It relies on a resistor and capacitor to determine the frequency of oscillation. RC oscillator
• Types of RC oscillator. Wien bridge oscillator, Phase shift oscillator, Twin-T oscillator
• It uses an op-amp and RC bridge circuit. Wien bridge oscillator
• For oscillation to take place in Wien bridge oscillator, R4/R3 > 2
• A Wien bridge circuit is a lead-lag circuit
• It follows the basic development of a feedback circuit. LC oscillator
• The three RC circuits in the feedback loop can provide a maximum phase shift approaching 90 degrees.
• Oscillation occurs at the frequency where the total phase shift through the RC circuits is 180 degrees. (Out of phase)
• The feedback circuit attenuation for phase shift oscillator is 1/29
• To ensure proper oscillation for phase shift oscillator, A>29
• The combined parallel filters in Twin-T oscillator produces a bandstop or notch.
• The gain in Twin-T oscillator is greater than or equal to 100.
• It uses inductance and capacitance to generate sinusoidal waves. LC oscillators
• LC feedback elements are normally used in oscillator that require higher frequency in oscillation which is greater than 1MHz
• Types of LC oscillator: Armstrong, Colpitts, Hartley, Clapped
• It is used to produce a sine wave output of constant amplitude and fairly constant frequency within the RF range. Armstrong oscillator
• It uses an LC circuit to establish the frequency of oscillation. Armstrong oscillator
• Armstrong oscillator uses Class C amplifier with self-bias.