Acqiris SA230E, Руководство пользователя

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FAQ
Acqiris SA230E User's Manual 91
Chapter 9
FAQ
9.1 Q. What is coherent sampling? 91
9.2 Q. How to manage the internal temperature? 91
9.3 Q. What happens if the host processor goes in hibernation mode? 92
9.1 Q. What is coherent sampling?
A. Coherent Sampling refers to the relationship between the input frequency F
in
, sampling frequency
F
s
, number of cycles in the sampled set and the number of samples. With coherent sampling one is
assured that the signal power in an FFT is contained within one FFT bin (assuming a single input tone).
The condition for coherent sampling is given by:
F
in
/F
s
=N
cycles
/N
samples
For example if we have N
samples
= 2
11
, and F
s
= 100e6, and we expect and input frequency close to
F
s
/2, let's say F
in
= 44 MHz, then N
cycles
= 901.12 which is close to an integer. We could therefore
round down to N
cycles
= 901 and we would get F
in
= 43.994140625 MHz, which is an input frequency
that satisfies coherent sampling.
The integer number should be chosen carefully. We have three possible types of integers, even, odd,
and prime. Even is not a good idea since we would hit the same code every
M
samples
, where M can be
much less than N . Odd is a better idea since it takes longer to hit the same code. According to some
sources a prime number of cycles is the best (with the exception of the prime 2) because it takes a
long time before the same code repeats.
——————————————————————
9.2 Q. How to manage the internal temperature?
A. The operating temperature of the SA230E as specified in the SA230E datasheet, is the workstation
internal ambient temperature at intake of the ADC module.
The effective temperature limit is fixed by the maximum internal DPU temperature which should stay
below 100°C to guarantee FPGA proper operating.