Explanation of Nyquist sampling frequency

[pjames_e]

in a input frequency of 1Mhz
*nyquist tell that the fmax must be at least x2 the fs

and if i have fs of 1Mhz and must be have a 32 samples that this affect the fmax needed?

 

[echo47]

nyquist freq.

Nyquist says that your sample rate must be greater than two times the signal's bandwidth. In many systems bandwidth equals fmax, but that's not true in some systems, and it can make a big difference.

Please clarify your question about 32 samples. Number of samples is usually not a factor.

 

[gliss]

nyquist freq.

32 probably means 32-bit sample depth?

 

[pjames_e]

Re: nyquist freq.

a DSO with 32 sampling points.... do this affect the fmax

 

[gliss]

nyquist freq.

No, it doesn't.

 

[thusme42]

Re: nyquist freq.

Then what??

 

[pjames_e]

Re: nyquist freq.

you if i have an analog input of 1MHz and is to be sampled 32 times ii don't need a ADC that have a capable of a sampling rate of 32MSPS?

 

[gliss]

nyquist freq.

You'll want a ADC @ 2MHz with a sample depth of 32.

 

[leomecma]

Re: nyquist freq.

only to illuminate there it is the statement, as our friend echo47 had already exposed.

The Nyquist-Shannon sampling theorem is the fundamental theorem in the field of information theory, in particular telecommunications. It is also known as the Whittaker-Nyquist-Kotelnikov-Shannon sampling theorem or just simply the sampling theorem.

The theorem states that:

when sampling a signal (e.g., converting from an analog signal to digital), the sampling frequency must be greater than twice the bandwidth of the input signal in order to be able to reconstruct the original perfectly from the sampled version.
If B is the bandwidth and Fs is the sampling rate, then the theorem can be stated mathematically (called the "sampling condition" from here on)

2B < Fs

IMPORTANT NOTE: This theorem is commonly misstated/misunderstood (or even mistaught). The sampling rate must be greater than twice the signal bandwidth, not the maximum/highest frequency. A signal is a baseband signal if the maximum/highest frequency coincides with the bandwidth, which means the signal contains zero hertz. Not all signals are baseband signals (e.g., FM radio). This principle finds practical application in the "IF-sampling" techniques used in some digital receivers.

 

[checkmate]

Re: nyquist freq.

you if i have an analog input of 1MHz and is to be sampled 32 times ii don't need a ADC that have a capable of a sampling rate of 32MSPS?

I think you may have been a little confused over the nyquist criterion. In simpler words, it states that if you would like to sample an analog signal of one-sided bandwidth of f0, and be able to reproduce the analog signal later (without any loss of information, otherwise known as perfect reconstruction), then the sampling frequency must be at least 2f0.
In other words, for a sinusoidal input, all you have to ensure is that each period is sampled at least twice.
In your case, f0=1MHz. So the minimum sampling rate should be 2Msps. Of course, if you can afford 32Msps, all the better, though it's just overkill.