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Sampling theorem in Digital Storage oscilloscope

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cmos babe

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Sampling theorem

According to the sampling theorem in order to be able to reconstruct a signal from it's samples the sampling frequency should be at least twice the max frequency . But, why do they use 10 times the max frequency in Digital Storage oscilloscopes.

Thanks in advance.
 

Re: Sampling theorem

The theorem of the sampling establishes that the demuestreo frequency must be - to the less twice frequency of the signal original-but this sampling is ideal. The accomplishment of the sampling is with signals delta of Dirac.

The sampling that takes place in the reality is with rectangular pulses reason why the predicted value previously will not be sufficient.

It can that the idea goes that way.
 

    C

    cmos babe

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Re: Sampling theorem

cmos babe,
Digital scopes must provide an image that is easily interpreted by humans. This requires interpolating between samples. While it is true that the original signal can be re-constructed with a sampling frequency of only 2X the input frequency, the reconstruction would require an ideal "brickwall" filter.
Regards,
Kral
 

    C

    cmos babe

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Re: Sampling theorem

XNOX_Rambo said:
Just a correction - the sampling theorem states that the sampling frequency must
be at least twice the signal bandwith. Read more here:
h**p://www.answers.com/topic/nyquist-shannon-sampling-theorem?method=22
Click to expand...
The bandwidth is the frequency of the max frequency component of a signal isn't it?
 

Re: Sampling theorem

The bandwidth is the frequency of the max frequency component of a signal isn't it?
Click to expand...
Only if the lowest frequency component is 0 Hz... :wink:

"...because Nyquist actually said the sampling rate must be at least double the signal’s bandwidth, not the signal’s highest frequency component. For a signal that contains frequencies reaching from DC to 40 MHz, for example, the Nyquist criterion reduces to the common definition, and the sample rate must be at least 80 MS/s. However, for a signal that contains frequencies between 30 MHz and 35 MHz, the required sample rate is only 10 MS/s, double the 5 MHz bandwidth."

The quote comes from here:
https://digital.ni.com/worldwide/bw...AF86256F9E00593AD2?opendocument&node=12601_us
 

    C

    cmos babe

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Re: Sampling theorem

"According to the sampling theorem in order to be able to reconstruct a signal from it's samples, the sampling frequency should be at least twice the max frequency"
This is true only for Low pass signals.So bandwidth n highest frequecy both comeout to be same.
The definition differs for bandpass signals.

One important condition for sampling theorem which everyone neglects is "2fc" condition is valid only if the FT of lowpass signal is not impulse.

In oscilloscope also it need not be 10 times according to me.But I am not sure though.

I hope this helps u.
 

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