Amplifier Frequency Response and Bandwidth Quiz Quiz

Evaluate your understanding of amplifier frequency response and bandwidth with this five-question quiz, covering key concepts such as gain, cutoff frequencies, and circuit behaviors. Perfect for learners and professionals seeking to reinforce their knowledge of audio electronics and signal processing.

1. Cutoff Frequency Identification

   In a typical voltage amplifier, what is the lower cutoff frequency, often labeled fL, in the context of frequency response?

   1. The frequency where power output becomes zero
   2. The frequency where amplifier gain falls to 70.7% of the midband value
   3. The frequency at which output voltage reaches its maximum
   4. The frequency where the input resistance doubles

   Explanation: The lower cutoff frequency (fL) is defined as the frequency at which the amplifier's gain drops to 70.7% (or -3 dB) of its midband or maximum value. This point marks the lower limit of effective amplification within the bandwidth. The gain does not necessarily correspond with changes in resistance (option B), nor is it marked by maximum output voltage (option C), or zero power output (option D), as these do not directly define cutoff frequency.

2. Effect of Coupling Capacitor

   If the value of a coupling capacitor in an amplifier circuit is decreased, what is the likely effect on the amplifier's low-frequency response?

   1. The bandwidth remains unchanged
   2. All frequencies are amplified equally
   3. The higher cutoff frequency decreases
   4. The lower cutoff frequency increases

   Explanation: Decreasing the coupling capacitor reduces its ability to pass low-frequency signals, resulting in a higher lower cutoff frequency and reduced low-frequency gain. This does not affect the upper cutoff frequency (option B), nor does it mean all frequencies are equally amplified (option C). The bandwidth changes because one end has shifted (option D), so it does not remain unchanged.

3. Bandwidth Definition

   Which of the following best describes the bandwidth of an amplifier when given a frequency response curve?

   1. The difference between the upper and lower -3 dB cutoff frequencies
   2. The sum of all frequencies that the amplifier can process
   3. The peak output voltage frequency
   4. The mean value of all frequency gains

   Explanation: Bandwidth is defined as the range of frequencies between the lower and upper -3 dB (cutoff) points where gain drops to 70.7% of its maximum. The mean gain (option B) does not define bandwidth, nor does simply summing frequencies (option C). The peak output voltage (option D) usually occurs within the passband but does not describe bandwidth.

4. Miller Effect and High-Frequency Response

   How does the Miller effect influence the high-frequency response of a common-emitter amplifier with significant interelectrode capacitance?

   1. It has no impact on frequency response
   2. It decreases the upper cutoff frequency, narrowing bandwidth
   3. It improves low-frequency amplification
   4. It makes input impedance infinite

   Explanation: The Miller effect increases the effective input capacitance due to feedback, which lowers the upper cutoff frequency and thus narrows bandwidth. It does not improve low-frequency amplification (option B), nor is its effect insignificant (option C). The input impedance does not become infinite as in option D; in fact, the input impedance may decrease with higher capacitance.

5. Gain Behavior Outside Bandwidth

   What typically happens to an amplifier’s voltage gain at frequencies much higher than its upper cutoff frequency?

   1. The gain stays constant at its midband value
   2. The gain increases due to inductive coupling
   3. The gain drops rapidly due to capacitive effects
   4. The gain oscillates unpredictably

   Explanation: At frequencies above the upper cutoff, the amplifier's voltage gain decreases sharply because parasitic capacitances dominate, impeding signal transfer. The gain does not remain constant as in option B, nor does it typically increase due to inductive effects (option C). Oscillations (option D) can occur in some unstable circuits, but the standard response is a rapid falloff due to capacitance.