Amplifier Frequency Response Interview Questions and Answers:
1. What is meant by frequency response of an amplifier?
Ans. The frequency response is the graph of voltage gain versus input frequency.
2. What is midband range?
Ans. The midband range is the region where coupling and bypass capacitors act as short circuits, and stray and transistor capacitances act as open circuits. In this region, the voltage gain is almost a constant.
3. Define half-power frequency.
Ans. The frequency at which the power is reduced to one-half of the maximum amplitude, is known as half-power frequency.
4. Define bandwidth and gain of an amplifier.
Ans. The frequency response of an amplifier signifies different range of frequencies. The low frequency and high frequency at which power is reduced to one-half of the maximum amplitude are defined as cutoff frequencies or -3 dB frequencies. The difference of the half-power points or -3 dB frequencies is known as bandwidth of the amplifier.
An amplifier amplifies small signal into large signal at the output. The change in amplitude may be in voltage, current or power. The ratio of amplitudes of output and input signals is termed as the gain of the amplifier.
5. What do you mean by gain-bandwidth product?
Ans. For any amplifier, the product of bandwidth and gain at mid-frequencies is known as gain-bandwidth product. For any amplifier, it is constant and is equal to fT.
6. Why sometimes, in frequency response plot, it becomes necessary to plot frequency on logarithmic scale?
Ans. The frequency plot on logarithmic scale, in case of frequency response plot, becomes necessary so as to accommodate large frequency ranges. On a linear graph it would be impossible to plot any large range of frequencies (for example 1 Hz to 1 MHz) on a single graph. So the horizontal axis on frequency response plots is normally scaled logarithmically.
7. Define the unit decibel for expressing (i) voltage (ii) current and (iii) power.
Ans. Decibel voltage gain is defined as 20 times the common logarithm of the voltage gain i.e.,
Av(dB) = 20 log10 Av.