Oscillator MCQ Quiz With Answers

The decibel is a unit used to measure the relative signal strength. It is commonly used in telecommunications and audio systems to quantify the difference in power between two signals. The decibel scale allows for a logarithmic representation of signal strength, making it easier to compare and analyze different signal levels. Therefore, the correct answer is "relative signal strength."

In an oscillator circuit, the feedback should be just enough to sustain oscillation. This means that the amount of feedback should be carefully controlled so that it provides the necessary energy to maintain oscillation without causing instability or damping. Too much feedback can lead to over-amplification and distortion, while too little feedback can result in insufficient energy to sustain oscillation. Therefore, finding the right balance of feedback is crucial for the proper functioning of an oscillator circuit.

The frequency at which a quartz crystal oscillator produces energy is largely dependent on the physical thickness of the quartz wafer. The thickness of the wafer determines the resonant frequency of the crystal, as it affects the speed at which the crystal vibrates. A thicker wafer will vibrate at a lower frequency, while a thinner wafer will vibrate at a higher frequency. Therefore, the physical thickness of the quartz wafer directly influences the frequency produced by the oscillator.

A class C amplifier is always nonlinear because it operates with less than 50% of the input signal cycle. This means that it does not reproduce the entire input waveform accurately, resulting in distortion. Regardless of any adjustments or modifications, a class C amplifier cannot be made linear.

In a Class B FET amplifier, the drain current flows for exactly 50 percent of the signal cycle. This is because in Class B amplifiers, the FET conducts current only when the input signal exceeds a certain threshold, typically around zero volts. This means that the FET is only active during half of the input signal cycle, resulting in a drain current flow of 50 percent.

An RF choke is a type of inductor that is designed to block high-frequency signals (RF signals) while allowing direct current (dc) to pass through. This is achieved by using a coil of wire to create a magnetic field that opposes the flow of RF signals, effectively blocking them. However, since direct current does not change in frequency, it is not affected by the magnetic field and can pass through the choke. Therefore, an RF choke passes dc but blocks RF signals.

A power gain of 44 dB means that the output power is 25,000 times greater than the input power. This can be calculated by using the formula: Power Gain (in dB) = 10 * log10(Output Power/Input Power). In this case, 44 = 10 * log10(Output Power/Input Power), which can be rearranged to find that the Output Power/Input Power ratio is 25,000:1.

A gain figure of -15 dB indicates a decrease in signal strength. dB is a logarithmic scale, so a negative value means a decrease in magnitude. Therefore, the output signal is weaker than the input signal, making the statement "The input signal is stronger than the output signal" true.

Class B amplification is a technique used to minimize distortion in audio applications. By connecting two identical bipolar transistors or FETs in a push-pull configuration, both transistors are biased exactly at cutoff or pinchoff, ensuring that each transistor operates in its active region for half of the input waveform. This configuration allows for efficient power utilization and eliminates the need for a biasing voltage, resulting in a pure sine wave output with low distortion.

In-phase feedback is not a reason for an oscillator to fail to start. In fact, feedback is necessary for an oscillator to sustain oscillations. It provides the necessary positive feedback to compensate for energy losses and maintain the desired oscillation frequency. Therefore, in-phase feedback is not an exception and cannot be a reason for an oscillator to fail to start.

A graphic equalizer is a device that allows users to adjust the tone of audio signals in an amplifier. It consists of multiple bands, each representing a specific frequency range, which can be individually adjusted to boost or attenuate the corresponding frequencies. This allows users to shape the overall sound by emphasizing or reducing certain frequencies. Therefore, the given answer accurately describes the function of a graphic equalizer as a tone control that can be used in an audio amplifier.

Since the bipolar-transistor PA is 66 percent efficient, it means that 66 percent of the input power is converted into output power. Therefore, to find the dc collector power input, we can divide the output power by the efficiency percentage. In this case, 33 W divided by 0.66 (66 percent as a decimal) equals 50 W. Hence, the correct answer is 50 W.

A frequency synthesizer is a device used to generate precise and stable frequencies. It is important for the synthesizer to maintain stability in order to ensure accuracy and reliability in frequency generation. This stability allows the synthesizer to produce consistent and reliable output frequencies over time, without significant variations or drift. This is crucial in various applications such as telecommunications, radar systems, and scientific research, where precise and stable frequencies are required for proper functioning. Therefore, the exceptional stability of a frequency synthesizer is a desirable characteristic that sets it apart from other devices.

The optimum capacitance values in an amplifier circuit depend on the input signal frequency. This is because different frequencies require different amounts of capacitance to achieve optimal performance. Higher frequencies typically require smaller capacitance values, while lower frequencies require larger capacitance values. By selecting the appropriate capacitance values for the input signal frequency, the amplifier circuit can effectively amplify the desired frequency range and minimize distortion or loss of signal quality.

An RF oscillator usually has most or all of its energy at a single frequency. This means that the oscillator generates a signal that is concentrated at a specific frequency, rather than being spread out across a range of frequencies. This is important in RF (radio frequency) applications, where a specific frequency is desired for communication or transmission purposes. By having most of its energy at a single frequency, the RF oscillator can provide a stable and reliable signal for these applications.

If the impedance of the load connected to the output of an oscillator is extremely high, it is no cause for concern; in fact, it is a good thing. This is because a high load impedance ensures that the oscillator is isolated from the load, preventing any unwanted interactions or disturbances. It allows the oscillator to operate independently and maintain its stability, without being affected by the load. Therefore, a high load impedance is desirable in this scenario.

Class AB2 amplifiers have some distortion in the signal wave because the collector current is present during most, but not all, of the cycle. In Class AB2 amplifiers, the active device conducts for more than half of the input cycle, but less than the full cycle. This results in some distortion in the signal wave. Class AB2 amplifiers are commonly used in audio applications where moderate distortion is acceptable, such as in power amplifiers for music systems.

An oscillator at RF requires the use of a stage with gain because an oscillator is a device that generates a continuous output signal without any input signal. In order to sustain oscillation, the circuit needs to provide positive feedback, which is achieved by having a stage with gain. The gain in the circuit compensates for any losses and ensures that the output signal is continuously amplified and fed back to the input, resulting in the desired oscillation. The other options, such as a common drain or common collector circuit, a tapped coil, or a quartz crystal, are not essential components for generating oscillation in an RF oscillator circuit.

A tuned RF PA must be adjusted for maximum power output because this ensures that the power amplifier is operating at its highest efficiency and delivering the maximum amount of power to the load. By adjusting the PA for maximum power output, the system can achieve optimal performance and transmit signals with the highest possible power level. This is important in applications where high power transmission is required, such as in wireless communication systems or broadcasting.