Amplifier and Oscillator Circuits Flashcards
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Read the first 7 Amplifier and Oscillator Circuits flashcards as text
In a Colpitts oscillator, the frequency-determining tank circuit consists of:
Answer: Two capacitors and one inductor
The Colpitts oscillator uses a capacitive voltage divider formed by two capacitors and a single inductor as its tank circuit.
What distinguishes a Hartley oscillator from a Colpitts oscillator?
Answer: A Hartley oscillator uses a tapped inductor in its tank circuit
The Hartley oscillator uses a tapped (center-tapped) coil as its inductive element, while the Colpitts uses two capacitors as its voltage divider.
Why are crystal-controlled oscillators preferred in commercial radio transmitters?
Answer: They provide superior frequency stability compared to LC oscillators
Crystal oscillators exploit the piezoelectric properties of quartz to achieve very high frequency stability compared to LC circuits.
The Barkhausen criterion states that for sustained oscillation, the total loop gain must be:
Answer: Equal to unity with a total phase shift of 0° or 360°
For sustained oscillation, the amplifier gain must exactly compensate for feedback network losses, and the total phase shift around the loop must be 0° or a multiple of 360°.
Which oscillator circuit is commonly used with a quartz crystal because it requires only one active device and connects the crystal directly in the feedback path?
Answer: Pierce oscillator
The Pierce oscillator connects the crystal directly in the feedback path between drain and gate with minimal external components, making it very practical for crystal-controlled designs.
In a three-section RC phase-shift oscillator, what is the total phase shift contributed by the RC ladder network?
Answer: 180°
Each RC section provides 60° of phase shift; three sections together provide 180°, and the amplifier's inversion provides the remaining 180° for the required 360° total.
A Clapp oscillator improves on the Colpitts design primarily by:
Answer: Adding a series capacitor with the inductor to reduce the effect of transistor capacitance variations
The Clapp oscillator adds a small series capacitor to the inductor in the tank circuit, isolating the oscillation frequency from transistor parasitic capacitance changes.