Here are the answers for the June 2017 StudentZone Quiz
Q: Which Noise is generated in a Resistor?
A: White Noise
Thermal noise in an ideal resistor is approximately white noise. The power spectral density is nearly constant throughout the frequency spectrum.
Q: What is the rms noise generated by a 10kΩ resistor at room temp (20°C) over an equivalent noise bandwidth of 20 kHz.
Solution:
Keep in mind this model
with V(rms)=sqrt(4*KB*T*R*B)
B= Bandwidth (F2-F1) [Hz]
R= Resistor [Ohm]
T= Temperature [Kelvin]
KB= Boltzmann Constant
Vrms=1.79uVrms
Q: Having a 24Bit Audio ADC with an Input span of 2.5V – how many flickering Bits we would get with this Vnoise from above?
Calculation:
For the calculation we need Vp-p.
I convert the 1.79uVrms into 11.87uVp-p by multiplying by ~ 6.6
(A factor of 6 is sometimes used here instead of 6.6, but ADI has standardized on 6.6)
1 LSB for a 24bit ADC and 2.5V Fullscale equals to 0.149uV.
So there are 11.87uV/0.149uV = 80 -> this means 80LSBs flickering which is around 6.2 bits being not stable.
Remark:
There is the argument that since the noise is Gaussian, there is a probability that more bits will occasionally flicker.
(but you can’t really see that effect with the eye)
