6.1 State TWO categories of amplifiers - NSC Electrical Technology Electronics - Question 6 - 2022 - Paper 1

The maximum voltage across the collector terminal can be determined from the characteristic curve in FIGURE 6.2, which shows that the maximum collector voltage is 20 V.

Using the formula: $I_C = \frac{V_{CE}}{R_C}$ Substituting the maximum collector voltage (20 V) into the equation, we have: $I_C = \frac{20}{\text{R}_C}$ Assuming a resistance value of 3.33kΩ, we find: $I_C = \frac{20}{3.33 \times 10^3} = 6 mA$

The load line can be drawn by intersecting the maximum collector current with the maximum voltage, indicating the operational point where the amplifier functions optimally.

The Q-point (quiescent point) should be marked at the intersection of the load line with the characteristic curves where the amplifier stabilizes.

As the bias point in Class A operation is typically set at the middle of the load line, the collector current can be determined as approximately 3 mA.

Rs and Rb function as voltage dividers that set the base bias voltage for transistor Q1, ensuring it operates in the active region.

The coupling capacitors are selected to be large to allow a wide frequency response and to block DC voltage while allowing AC signals to pass between stages of amplification.

Re is used to provide stability to the transistor biasing by negating variations in collector current, thus stabilizing the operating point.

RC coupling enables each amplifier stage to maintain its own DC operating point independently while allowing AC signals to pass through without interference from neighboring stages.

An application of the transformer-coupled amplifier is in audio amplification systems, where impedance matching is necessary.

1. Transformer normalization allows for better impedance matching.
2. It prevents DC feedback between stages, enhancing stability.

1. AC motor
2. Relay.

Ce is used to shunt the AC signal to ground, thereby preventing any high-frequency signals from affecting the amplifier's operation.

The radio-frequency amplifier selects and amplifies radio signals while providing necessary gain and ensuring minimal distortion.

Variable pre-set capacitors allow for tuning of the amplifier's frequency response to match the desired operational frequency.

When switch S is moved to position 2, the capacitor C will discharge, creating damped oscillations that decay over time.

The voltage waveform will initially spike and then decay exponentially, resembling a damped oscillation.

The frequency can be increased by decreasing the values of the inductor L or the capacitor C in the tank circuit.

The Hartley oscillator is commonly used in radio frequency applications to generate stable sine wave signals.

C1 and C2 serve to couple signals between the oscillator circuit and the tank circuit as well as block DC voltage.

The state of oscillation is maintained through positive feedback from the collector of the transistor back to the tank circuit.

Transistor Q1 serves to provide a 180-degree phase shift necessary for oscillation in the circuit.

Frequency can be adjusted by changing the capacitance values of the components C1, C2, or other capacitors in the circuit.

Transistor amplifiers typically use negative feedback to stabilize gain, while oscillator circuits use positive feedback to sustain oscillations.

LC oscillators generate high-frequency signals, while RC oscillators are used to generate lower frequency signals due to their reliance on capacitive reactance.