dSPACE DS1103, Руководство по установке и настройке оборудования

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ADC Performance of dSPACE Boards
We are frequently contacted because of the “poor” performance of
the A/D sections of our boards. This is usually derived from looking at
the noisy signal traced in ControlDesk 3.x or ControlDesk
Next Generation when sampling an unconnected A/D input or an A/D
input shorted to ground. However, this has nothing to do with the
definition of the SNR (signal
‑
to
‑
noise
‑
ratio) we publish in the data
sheets of our boards.
A common misunderstanding is that theoretical maximum values of
ideal ADCs are expected from real
‑
world components in real
‑
world
board designs, even inside PC environments. This is impossible. A
16
‑
bit ADC, for example, never has an effective number of bits equal
to 16.
The A/D section of every dSPACE board is FFT (Fast Fourier Transform)
tested during production so that we can guarantee the published
data sheet values for every board. For 16
‑
bit ADCs we typically
achieve an SNR of 78 … 82 dB depending on the board type. This
corresponds to an effective number of bits of about 12.5 … 13. This
is the best that can be achieved in typical PC environments.
For background information, refer to:
n
The following chapters
n
“Noise Reduction Techniques in Electronic Systems” by Henry W.
Ott, John Wiley & Sons, Inc.
Objective
Information in this section
Definition of SNR 202
Notes on Measuring Noise 203
Definition of SNR
SNR (signal
‑
to
‑
noise
‑
ratio) is defined as a true rms (root mean square)
ratio between the input signal and the noise. SNR is usually expressed
in dB.
Objective
Where to go from here
s
General Notes and Tips on Signal Conditioning
t
202
s
DS1103 Hardware Installation and Configuration November 2014