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Using DFT to analyze a time-interleaving track and hold circuit

YutaoLiu over 5 years ago

Hi,

I am evaluating the frequency response and linearity of a time-interleaving track and hold circuit.

The input signal frequency can be up to 28GHz, and the sampling frequency (Fs) is 7GHz.

In my test bench, I set the sample number (Ns) as 64, and the input frequency is set with the formula Fin = (Ni/Ns)xFs, while Ni is prime number, the strobe period is set as "1/8/Fs". In the DFT setting, the starting point is set as "50/Fs", and the end point is 50/7G+Ns/Fs. In this way, the sampling frequency in DFT is the same as that in real circuit.

My question is:

1. For the input signal, whose frequency is higher than Fs/2, its fundamental tone would be folded back to 0~Fs/2 due to aliasing. Can I still use DFT to capture the fundamental tone and its harmonics magnitude correctly? Is it possible that the harmonics overlap with each other? If so, how should I set the input frequency to avoid this problem?

2. Can "Spectrum Measurement Tool" in ADE can capture the correct fundamental tone while signal frequency is higher than sampling frequency?

Thanks and regards,

Yuto

Andrew Beckett over 5 years ago

This sounds more like a fundamental need for understanding sampling in general. It's nothing to do with ADE per se. Perhaps you need to understand abouthttps://en.wikipedia.org/wiki/Coherent_sampling? Even then, you cannot distinguish between the multiple frequencies that alias to the same frequency below the Nyquist frequency.
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