5.1 Define the following terms with reference to amplifiers: 5.1.1 Feedback 5.1.2 Distortion 5.2 Refer to FIGURE 5.2 below and answer the questions that follow - NSC Electrical Technology Electronics - Question 5 - 2020 - Paper 1

Distortion refers to any alteration of the original signal as it passes through the amplifier. This unwanted change often occurs when the amplifier operates outside its linear range, leading to a change in amplitude or waveform shape.

The amplifier in FIGURE 5.2 is identified as a Common Emitter Amplifier.

In Class A amplification, the emitter-base junction is forward biased to the cut-off region and above the saturation region. This ensures that the transistor operates in the active region throughout the entire signal cycle, allowing for high fidelity amplification.

To find the voltage drop across R_C, we can use the formula:

$V_{RC} = V_{CC} - V_{CE}$

Substituting the values:

$V_{RC} = 9 V - 2.38 V = 6.62 V$

The voltage gain (A_V) in decibels can be calculated using:

A_V = 20 imes ext{log}_{10}rac{V_{out}}{V_{in}}

Given that V_{out} = 2.38 V and V_{in} = 2 mV:

A_V = 20 imes ext{log}_{10}rac{2.38}{0.002} = 61.51 dB

An increase in V_{IN} will lead to a rise in V_{BE}, causing the transistor to conduct more current. This reduces the resistance of the transistor and shifts the Q point higher, ultimately leading to a decrease in V_{CE} as the output voltage approaches saturation.

The oscillator in FIGURE 5.6 is identified as a Colpitts oscillator.

Oscillation is achieved when the tank circuit charges and discharges, allowing the output to produce a sine wave. The transistors switch states due to the feedback from the tank circuit, driving oscillations.

Feedback is obtained through the collector terminal of the transistor, which is connected to the resonating circuit. This feedback is 180 degrees out of phase with the input signal, ensuring consistent oscillation.

Inductor L_3 acts as a RF choke that prevents AC resonant signals from affecting the DC supply. It ensures that the oscillation frequency remains stable and prevents signal degradation.

FETs minimize loading effects compared to BJTs, allowing for a higher input impedance in oscillator circuits. This helps maintain signal integrity and prevents distortion.

1. Both produce a pure sinusoidal output waveform.
2. Both utilize a transistor for amplification and positive feedback to sustain oscillations.