Noise Analysis
Johnson (thermal), shot, and 1/f noise, signal-to-noise ratio
Parameters
1. What distinguishes Johnson (thermal) noise from shot noise?
A. Thermal noise arises from random thermal motion of electrons in any resistance, even without current; shot noise requires discrete charges crossing a potential barrier
B. They are identical, just with different names
C. Thermal noise only occurs in diodes
D. Shot noise depends only on temperature
2. Why is 1/f noise particularly problematic for low-frequency measurements?
A. Its power spectral density increases as frequency decreases ($\propto1/f$), so at low frequencies it can substantially exceed the white noise floor
B. It only exists at high frequencies
C. It is independent of current
D. It only depends on temperature
3. Why does a MOSFET typically have a higher 1/f noise corner frequency than a bipolar transistor?
A. MOSFET current flows near the surface, close to trap states at the gate oxide interface, increasing 1/f noise; BJT current flows through the bulk, far from interfaces
B. MOSFETs are always hotter
C. MOSFETs have no thermal noise at all
D. This is purely a manufacturing defect with no physical basis
4. If you double the measurement bandwidth (with the same white noise density), what happens to the total noise power?
A. It doubles (power is linearly proportional to bandwidth)
B. It stays the same
C. It quadruples
D. It halves