Signal to noise ratio for thermal and shot noise

AI Thread Summary
The discussion focuses on calculating the signal-to-noise ratio (SNR) for a sensor output connected to an RC circuit at 300K. The voltage across the capacitor is calculated as 624.15V, and the power of the signal is determined to be 7791.2 J. Participants emphasize the need to calculate the power of noise, considering both thermal noise and shot noise, but express confusion regarding the bandwidth and the interpretation of the 10,000 electrons. Clarifications are provided about the correct voltage formula for a capacitor and the relationship between the RC filter and noise bandwidth. The conversation highlights the importance of accurately determining both thermal and shot noise contributions to achieve a comprehensive SNR calculation.
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Homework Statement


The output of a sensor which produces 10000 electrons is connected to parallel RC circuit with Resistance= 50 ohm, and the capacitance=10pF.
Calculate the signal to noise ratio at temperature 300K.


Homework Equations


SNR= 10 log (power of signal/ power of noise)
Or SNR = 20log ( voltage signal / voltage noise)



The Attempt at a Solution


Voltage=C/Q=624.15V
Power of signal= voltage square / resistance= 7791.2 J
But how to calculate power of noise? The thermal noise = 4kTf, where k is boltzman constant, f is frequency bandwidth. Yet not given , but I can only think of these formula for thermal noise and 10000 electron need to include shot noise?

Please help
 
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Check your equation for the voltage on a capacitor--it's not quite right. Then use this hint: the noise bandwidth is determined by the RC filter.
 
Is that 10,000 electrons or 10,000 electrons per second?
 
marcusl said:
Check your equation for the voltage on a capacitor--it's not quite right. Then use this hint: the noise bandwidth is determined by the RC filter.

Yup, V =Q/C , and f=1/(2∏RC)
But why is this the Bandwidth? The impedance of capacitor is same as resistance so we get maximum power for?
And 10000 electrons need to consider shot noise? If I consider, so I just add thermal noise voltage and shot noise together to get the total voltage noise?
 
rude man said:
Is that 10,000 electrons or 10,000 electrons per second?
10000 electrons without telling time, but even telling time, I still can calculate the thermal and shot noise.
 
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