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

One advantage of class AB push-pull amplifiers is that they reduce cross-over distortion, thereby allowing for more linear amplification and better overall sound quality.

To find the quiescent collector current (Ic) when the base current (Ib) is given as 20 μA, we use the formula: I_C = eta imes I_B Assuming a typical current gain (β) of around 20, the calculation is: $I_C = 20 imes 20 μA = 400 μA$

The quiescent voltage (Vce) can be determined from the load line of the transistor circuit. Given the Vcc of 20V and calculated Ic, we can find Vce at the quiescent point to be approximately 10V.

1. Distortion of the output waveform may occur, leading to reduced sound fidelity.
2. The transistor may be subjected to thermal runaway, which could ultimately damage the component.

One disadvantage of the RC-coupled amplifier is that it is unsuitable for low-frequency amplification, as it tends to block or attenuate lower frequency signals.

When the temperature of a transistor rises beyond its normal operating point, increased leakage current can cause the device to enter thermal runaway, potentially damaging the transistor due to excess power dissipation.

The RC-coupled network allows higher frequency signals to pass while blocking DC (low frequency) signals, effectively functioning as a low-pass filter.

A typical frequency response curve of an RC-coupled amplifier shows a gain plateau at mid frequencies, a roll-off at both high and low frequencies, indicating its bandwidth.

One disadvantage is the poor frequency response at high audio frequencies, where the amplifier may struggle to accurately reproduce sounds.

The impedance matching transformer is crucial because it maximizes power transfer from the amplifier to the speaker by matching their impedance levels.

1. C1 allows AC signals to pass through while blocking DC signals.
2. It helps filter out unwanted noise and fluctuations in the signal.

The output waveform is inverted due to the phase shift introduced by the transistor configuration, and it is amplified due to the gain characteristics of the circuit components.

One advantage of the amplifier in FIGURE 6.6 is that it produces a much larger output signal than a single Class A biased transistor amplifier.

Cross-over distortion can be minimized by biasing the two push-pull transistors into class AB mode, allowing both transistors to conduct slightly during the transition.

During the negative half cycle, the transistor Q2 turns ON while Q1 turns OFF, allowing the current to discharge through Q2 and generating an output pulse.

The frequency response curve is derived from a radio-frequency amplifier circuit.

Bandwidth is the range of frequencies within which the amplifier functions effectively, defined as the difference between the upper and lower cutoff frequencies, f1 and f2.

The resonant frequency can be altered by varying the values of the capacitor or inductor in the tank circuit, which directly influences the oscillation frequency.

One application of the Colpitts oscillator is in receivers for radio and television transmission.

The tank circuit is responsible for determining the frequency of oscillations in the oscillator.

The oscillation frequency (f0) can be calculated using the formula: f_0 = rac{1}{2 ext{π} imes ext{sqrt}(L imes C)} Plugging in values, we have: f_0 = rac{1}{2 ext{π} imes ext{sqrt}(200 imes 10^{-3} imes 150 imes 10^{-6})} = 29.06 ext{ Hz}

The type of feedback used is positive feedback.

Each RC combination produces a phase shift of 60 degrees.

The frequency of oscillation can be calculated using: f_0 = rac{1}{2 ext{π} imes ext{sqrt}(R_1 imes R_2 imes R_3 imes C_1 imes C_2 imes C_3)} Substituting the known values: f_0 = rac{1}{2 ext{π} imes ext{sqrt}(2*10^{4} (10^{-3})^2)} = 20.54 ext{ Hz}

Attenuation refers to the decrease in the output voltage compared to the input voltage. It describes the loss of signal strength as it passes through an amplifier or other circuit elements.