AdvancedA-002-009-005
A frequency multiplier circuit must be operated in:
C
Answer
Circuit design and power supplies
Type
A
class A
B
class AB
C
class C
D
class B
Answer Notes
A frequency multiplier relies on the generation of harmonics to function. Class C amplifiers are highly non-linear, conducting for less than 180 degrees of the input signal cycle. This severe clipping creates a heavily distorted output waveform that is extremely rich in harmonics.
Once these harmonics are generated by the Class C amplifier, a resonant output circuit can be tuned to select the desired harmonic (such as the second or third multiple of the fundamental frequency), effectively multiplying the frequency.
Classes A, AB, and B are designed to be much more linear to preserve signal fidelity and minimize harmonic distortion. Because they suppress the very harmonics a multiplier needs, they are unsuitable for this application.
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In a frequency multiplier circuit, the input signal is coupled to the base of a transistor through a capacitor. A radio frequency choke is connected between the base of the transistor and ground. The capacitor is:
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In a frequency multiplier circuit, an inductance (L1) and a variable capacitor (C2) are connected in series between VCC+ and ground. The collector of a transistor is connected to a tap on L1. The purpose of the variable capacitor is to: