Question 3-20C2

Parasitic oscillations are unwanted, self-sustaining oscillations in an amplifier, often at frequencies much higher than the intended operating frequency. They arise from stray capacitances and inductances within the circuit forming unintended resonant feedback loops. Installing a small variable capacitor in a strategic location, such as indicated by a dashed line in an RF amplifier circuit, allows for the introduction of controlled feedback. This capacitor can be precisely adjusted to provide negative feedback at the specific frequency of the parasitic oscillation. This negative feedback effectively cancels out the unwanted positive feedback that causes the oscillation, a technique known as neutralization. By damping or eliminating these unwanted resonant modes, the capacitor decreases parasitic oscillations, leading to a more stable and efficient amplifier. Options A and B are incorrect because increasing gain or increasing parasitic oscillations are not the primary, desired outcomes when using a capacitor in this manner to address oscillations. Crosstalk (D) refers to unwanted signal coupling between different signal paths, which is a separate issue from internal amplifier instability.