Calculating the size of a capacitor in a sample and hold circuit

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SUMMARY

The discussion focuses on calculating the size of a capacitor in a sample and hold circuit, specifically addressing the relationship between signal-to-noise ratio (SNR), jitter power, and thermal noise power. The SNR is given as 60dB, which translates to a power ratio of 1000. The participant initially encounters a negative thermal noise power value, which is identified as a simple mathematical error. The correct approach involves using the equation SNR = Psignal/(Pjitter + PthermalNoise) to derive the capacitor size from the thermal noise power, equated to kT/C.

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  • Understanding of signal-to-noise ratio (SNR) calculations
  • Familiarity with thermal noise equations, specifically kT/C
  • Basic knowledge of jitter power in electronic circuits
  • Proficiency in mathematical operations and error checking
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  • Research the derivation of thermal noise power in electronic circuits
  • Learn about the implications of SNR in analog signal processing
  • Study the effects of jitter on signal integrity in sample and hold circuits
  • Explore capacitor sizing techniques based on noise analysis
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Electrical engineers, circuit designers, and students studying analog electronics who are involved in designing sample and hold circuits and optimizing performance through noise analysis.

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Homework Statement
In sampling system the sample rate is 500 Ms/s with an input signal of range of 1 V
peak−peak and a clock jitter of 1 ps rms . A performance of 60 dB is required for all
signals the Nyquist baseband. Calculate its size of the capacitor.
Relevant Equations
Analog-to-Digital Conversion by Marcel Pelgrom Book
First, I calculate the jitter power with an equation given in the book
1582481543814.png


Next, I calculate the signal power
1582481656848.png


Now, I know that SNR = Psignal/(Pjitter + PthermalNoise),
1582481688065.png


However, I seem to be getting a negative value for the thermal noise power?? My plan was to use this thermal noise power and equate it to kT/C to get my capacitor size. But the thermal power is negative??
What am I doing wrong?
 

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the thermal power is negative?? What do you calculate for the SNR?
 
sprog said:
the thermal power is negative?? What do you calculate for the SNR?

your SNR is stated as 60dB, so the factor 10^(60/20) yields 1000 fold power ratio, so your scaled Pjitter is around 0.0003

0.125 - 0.0003 is positive not negative simple math mistake?
 

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