6.1 Describe the term stabilization with reference to amplifiers - NSC Electrical Technology Electronics - Question 6 - 2024 - Paper 1

One disadvantage of class AB push-pull amplifiers is that they tend to produce cross-over distortion when switching between the two transistors.

To determine the quiescent collector current (Ic), we can use the formula:
I_C = eta imes I_B
Assuming a beta (β) value of 200, the quiescent collector current would be:
$I_C = 200 imes 20 imes 10^{-6} = 4 ext{ mA}$.

The quiescent voltage (Vce) across the transistor can typically be determined from the DC load line. Given standard configurations, the voltage is often found to be around 10V depending on load conditions and supply voltage.

Two undesirable effects of incorrect biasing include:

1. Distortion of the output signal due to improper operation in the active region.
2. Potential damage to the transistor from thermal runaway, leading to failure.

One disadvantage of the RC-coupled amplifier is that it is unsuitable for low-frequency applications due to its frequency response characteristics.

When the temperature of a transistor exceeds its normal operating point, increased leakage current may flow, potentially leading to thermal runaway and destruction of the transistor.

The RC-coupled amplifier blocks DC signals while allowing AC signals to pass. It exhibits a frequency response that diminishes effectively at lower frequencies, thus functioning as a low-frequency filter.

A disadvantage of the amplifier is that it often requires a larger and more expensive transformer, impacting the overall cost and spatial efficiency of the design.

The impedance matching transformer maximizes power transfer by ensuring that the output impedance of the amplifier matches the load impedance (e.g., a speaker), enhancing performance.

Two functions of capacitor C1 include:

1. Allowing AC signals to pass through while blocking DC signals.
2. Providing coupling between stages of amplification, maintaining signal integrity.

The output waveform is inverted because the transistor is configured in common-emitter mode, where the phase of the output is opposite to that of the input, and it is amplified due to the gain characteristics of the transistor.

One advantage of the push-pull amplifier is its efficiency, as it can produce a larger output signal compared to a Class A amplifier while minimizing distortion.

Cross-over distortion can be minimized by biasing both transistors slightly into conduction, ensuring that neither transistor is completely off during the transition, which helps in maintaining linearity.

During the negative half cycle, one transistor (Q2) conducts while the other (Q1) turns off, allowing the load to be driven by the active transistor, providing a discharge path and maintaining the output waveform.

The frequency response curve is derived from a radio-frequency amplifier circuit, which typically exhibits a particular gain characteristic across a range of frequencies.

Bandwidth refers to the range of frequencies over which the amplifier operates effectively. The frequency response curve illustrates how gain decreases beyond the designated lower ($f_1$) and upper ($f_2$) frequency limits, creating a filter effect.

Resonant frequency can be modified by changing the values of the inductor or capacitor in the tank circuit; altering either component's value effectively shifts the resonant frequency.

One application of the Colpitts oscillator is in radio transmitters and receivers for generating stable oscillatory signals.

The tank circuit serves to determine the frequency of oscillations within the oscillator circuit, acting as a resonant circuit.

The oscillating frequency ($f_0$) can be calculated using the formula:
f_0 = rac{1}{2 ext{π} ext{√(LC)}}
Substituting the given values: f_0 = rac{1}{2 ext{π} ext{√(200 imes 10^{-3} imes 150 imes 10^{-6})}} \\ = 29.06 ext{ Hz}.

The feedback used in this configuration is positive feedback, which reinforces the initial input signal.

Each RC combination produces a phase shift of 60°, contributing to the overall phase shift needed for the oscillation to occur.

The frequency of oscillation ($f_0$) can be calculated using:
f_0 = rac{1}{2 ext{π}R ext{C}}
where R = R1 + R2 + R3 and C = C1 + C2 + C3: f_0 = rac{1}{2 ext{π}(3 imes 10^4)(3 imes 10^{-9})} \\ = 20.54 ext{ Hz}.

Attenuation is a reduction in signal strength. It occurs when the output voltage becomes smaller than the input voltage, often due to losses in the circuit components.