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Link between sampling and accuracy

yefj

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Hello, i have a track and hold circuit.My clock goes from 0-1V,C=15pf Vth=0.2V k=250[uA/V^2] (no body effect),as shown bellow.
What is the maximal clock frequency i can use to have 0.125*LSB accuracy at 14bit resolution?
Thanks.


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sutapanaki

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With this circuit you can't achieve 15 bit accuracy (or 0.125LSB at 14 bit level). There are way too many non-idealities.
 
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KlausST

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Hi,

first of all it depends on the voltage value of one LSB.
And this depends on the decoding range of your ADC. We don´t know this.
For sure there is also a dependency on the ratio, if you are looking for tau.

If you look only for the count of tau, then:
max allowed error = 0.125/(2^14)
1 tau gives an error of about 0.3768 = (1 / euler)

n = log(0.125/(2^14)) / log(0.3768)
(n is the count of tau you need, where tau = R x C)

*****

And it depends on the sampling time. We don´t know this. There is no need for 50% duty cycle.
We additionally don´t know how much conversion time (hold time) your ADC needs.

Klaus
 
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