2016-E7B: Amplifiers: Class of operation; vacuum tube and solid-state circuits; distortion and intermodulation; spurious and parasitic suppression; microwave amplifiers; switching-type amplifiers
For what portion of a signal cycle does a Class AB amplifier operate?
More than 180 degrees but less than 360 degrees
Exactly 180 degrees
The entire cycle
Less than 180 degrees
What is a Class D amplifier?
A type of amplifier that uses switching technology to achieve high efficiency
A low power amplifier that uses a differential amplifier for improved linearity
An amplifier that uses drift-mode FETs for high efficiency
A frequency doubling amplifier
Which of the following components form the output of a class D amplifier circuit?
A low-pass filter to remove switching signal components
A high-pass filter to compensate for low gain at low frequencies
A matched load resistor to prevent damage by switching transients
A temperature compensating load resistor to improve linearity
Where on the load line of a Class A common emitter amplifier would bias normally be set?
Approximately half-way between saturation and cutoff
Where the load line intersects the voltage axis
At a point where the bias resistor equals the load resistor
At a point where the load line intersects the zero bias current curve
What can be done to prevent unwanted oscillations in an RF power amplifier?
Install parasitic suppressors and/or neutralize the stage
Tune the stage for maximum SWR
Tune both the input and output for maximum power
Use a phase inverter in the output filter
Which of the following amplifier types reduces or eliminates even order harmonics?
Which of the following is a likely result when a Class C amplifier is used to amplify a single-sideband phone signal?
Signal distortion and excessive bandwidth
Reduced intermodulation products
Increased overall intelligibility
How can an RF power amplifier be neutralized?
By feeding a 180-degree out-of-phase portion of the output back to the input
By increasing the driving power
By reducing the driving power
By feeding an in-phase component of the output back to the input
Which of the following describes how the loading and tuning capacitors are to be adjusted when tuning a vacuum tube RF power amplifier that employs a Pi-network output circuit?
The tuning capacitor is adjusted for minimum plate current, and the loading capacitor is adjusted for maximum permissible plate current
The loading capacitor is set to maximum capacitance and the tuning capacitor is adjusted for minimum allowable plate current
The tuning capacitor is set to maximum capacitance and the loading capacitor is adjusted for minimum plate permissible current
The loading capacitor is adjusted to minimum plate current while alternately adjusting the tuning capacitor for maximum allowable plate current
In Figure E7-1, what is the purpose of R1 and R2?
In Figure E7-1, what is the purpose of R3?
Output load resistor
What type of amplifier circuit is shown in Figure E7-1?
In Figure E7-2, what is the purpose of R?
Why are switching amplifiers more efficient than linear amplifiers?
The power transistor is at saturation or cut off most of the time, resulting in low power dissipation
Switching amplifiers operate at higher voltages
Linear amplifiers have high gain resulting in higher harmonic content
Switching amplifiers use push-pull circuits
What is one way to prevent thermal runaway in a bipolar transistor amplifier?
Use a resistor in series with the emitter
Select transistors with high beta
All of these choices are correct
What is the effect of intermodulation products in a linear power amplifier?
Transmission of spurious signals
Creation of parasitic oscillations
All of these choices are correct
Why are odd-order rather than even-order intermodulation distortion products of concern in linear power amplifiers?
Because they are relatively close in frequency to the desired signal
Because they are relatively far in frequency from the desired signal
Because they invert the sidebands causing distortion
Because they maintain the sidebands, thus causing multiple duplicate signals
What is a characteristic of a grounded-grid amplifier?
Low input impedance
High power gain
High filament voltage
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