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Signal Connection to External Devices
DS1104 Hardware Installation and Configuration March 2004
153
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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 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:
■ Definition of SNR on page 154
■ Measuring Noise on page 155
■ “Noise Reduction Techniques in Electronic Systems” by Henry W.
Ott, John Wiley & Sons, Inc.
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