Noise Analysis and Distortion in Analog Circuits Quiz Quiz

Evaluate your understanding of noise analysis and distortion effects in analog circuits with this focused quiz. Explore key concepts such as noise types, measurement techniques, and distortion mechanisms relevant to effective analog circuit design and troubleshooting.

1. Sources of Noise in Resistors

   When analyzing the noise in a resistor within an analog amplifier, which type of noise is primarily considered over typical operating frequencies?

   1. Flicker noise
   2. Phase noise
   3. Thermal noise
   4. Burst noise

   Explanation: Thermal noise, also called Johnson noise, is the dominant noise source in resistors over most frequencies encountered in analog circuits. Flicker noise typically dominates at very low frequencies, but becomes negligible in mid to high frequency ranges. Burst noise occurs sporadically and is less relevant in continuous analysis. Phase noise is associated with oscillators and not passive resistors.

2. Definition of Total Harmonic Distortion

   In analog signal processing, what does the Total Harmonic Distortion (THD) metric quantify when measuring a circuit’s output?

   1. The difference between input and output voltage levels
   2. The bandwidth of the analog circuit
   3. The ratio of the sum of harmonic powers to the power of the fundamental frequency
   4. The root mean square of all noise sources

   Explanation: THD is defined as the ratio of the combined power of the harmonic frequencies to that of the fundamental frequency at the output, providing a measure of signal distortion. The difference between input and output voltage levels refers to gain or attenuation, not distortion. Bandwidth concerns frequency response. Noise sources are summed for noise analysis but are unrelated to THD.

3. Flicker Noise Characteristics

   Which statement best describes flicker noise, often observed in MOSFETs and BJTs at low frequencies?

   1. It is caused by temperature fluctuations alone
   2. It is only present when the device is powered off
   3. It persists uniformly across all frequencies
   4. It increases as frequency decreases and dominates at very low frequencies

   Explanation: Flicker noise, also known as 1/f noise, typically becomes stronger as the frequency decreases and is especially significant at low frequencies in transistors. It does not remain constant across all frequencies and is not solely caused by temperature effects. It is present when the device is active, not powered off.

4. Intermodulation Distortion Example

   If an analog circuit receives two tones at 2 kHz and 3 kHz and produces signals at 1 kHz and 5 kHz at its output, which type of distortion is being observed?

   1. Quantization noise
   2. Aliasing distortion
   3. Crossover distortion
   4. Intermodulation distortion

   Explanation: Intermodulation distortion occurs when multiple input signals mix, creating new frequencies that are sums and differences of the originals, such as 3 kHz minus 2 kHz (1 kHz) and 2 kHz plus 3 kHz (5 kHz). Aliasing is related to sampling and digital systems, not continuous analog mixing. Crossover distortion occurs in output stages of amplifiers. Quantization noise is a digital effect, not analog.

5. Effect of Bandwidth on Noise Power

   How does increasing the bandwidth of an analog amplifier affect the total output noise power, assuming all other parameters remain constant?

   1. It decreases the noise power
   2. It increases the noise power
   3. It eliminates all noise sources
   4. It has no effect on noise power

   Explanation: Wider bandwidth allows more noise frequencies to pass through, thereby increasing total output noise power. Reducing bandwidth would lower the total noise captured. Noise sources cannot be entirely eliminated by adjusting bandwidth alone. Saying it has no effect ignores the fundamental relationship between bandwidth and integrated noise.