CS5101A View Datasheet(PDF) - Cirrus Logic

Part Name

Description

Manufacturer

CS5101A

16-bit, 100 kSps / 20 kSps A/D Converters

Cirrus Logic 

CS5101A CS5102A

Figure 19. CS5101A FFT (SSC Mode, 1-Channel)

Figure 20. CS5101A FFT (SSC Mode, 1-Channel)

Figure 21. CS5102A FFT (SSC Mode, 1-Channel)

Figure 22. CS5102A FFT (SSC Mode, 1-Channel)

If sampling is not synchronized to the input sine

wave, it is highly unlikely that the time record will

contain an integer number of periods of the input

signal. However, the FFT assumes that the signal

is periodic, and will calculate the spectrum of a sig-

nal that appears to have large discontinuities,

thereby yielding a severely distorted spectrum. To

avoid this problem, the time record is multiplied by

a window function prior to performing the FFT. The

window function smoothly forces the endpoints of

the time record to zero, thereby removing the dis-

continuities.

The effect of the window in the frequency-domain

is to convolute the spectrum of the window with

that of the actual input.

The quality of the window used for harmonic anal-

ysis is typically judged by its highest side-lobe lev-

el. A five term window is used in FFT testing of the

CS5101A and CS5102A. This windowing algo-

rithm attenuates the side-lobes to below the noise

floor. Artifacts of windowing are discarded from the

signal-to-noise calculation using the assumption

that quantization noise is white. Averaging the FFT

results from ten time records filters the spectral

variability that can arise from capturing finite time

records without disturbing the total energy outside

the fundamental. All harmonics are visible in the

plots.

As illustrated in Figure 19, the CS5101A typically

provides about 92 dB S/(N+D) and 0.001% THD at

25 °C. Figure 20 illustrates only minor degradation

in performance when the ambient temperature is

raised to 138 °C. Figures 21 and 22 illustrate that

the CS5102A typically yields 92 dB S/(N+D) and

0.001% THD even with a large change in ambient

temperature. Unlike conventional successive-ap-

proximation ADC's, the signal-to-noise and dy-

namic range of the CS5101A and CS5102A are

DS45F6

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