Class 4 (4th Engineer) MET 📅 Oct 2022

Exam Question

(a) Explain the term bandwidth and describe the relationship between gain and badwidth (6)

(b) An amplifier has an open-circuit voltage gain of 1000, and input resistance of 2000Ω and and an output resistance of 1.0Ω. Determine the input signal voltage required to produce an output signal current of 0.5A in a 4.0Ω resistor connected across the output terminals. If the amplifier is then used with negative series voltage feedback so that one tenth of the output signal is fed back to the input, determine the input signal voltage to supply the same output signal current.

Reference Answer

### Part (a): Bandwidth and Gain-Bandwidth Relationship
#### Bandwidth
Bandwidth (BW) is a fundamental characteristic of an amplifier or any signal-processing system. It is defined as the range of frequencies over which the system's performance, specifically its gain, is within an acceptable range of its maximum value.
- **Definition**: The bandwidth is the difference between the upper and lower frequencies at which the amplifier's voltage gain drops to $$1/\sqrt{2}$$ (or approximately 70.7%) of its maximum, mid-band gain. These frequencies are known as the **half-power points** or **-3 dB points**.

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