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
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