DAC3282 datasheet(33/53 Pages) TI

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0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

-160

-140

-120

-100

-80

-60

-40

-20

f/fin

0.36 0.37 0.38 0.39 0.4 0.41 0.42 0.43 0.44 0.45 0.46

-0.5

-0.4

-0.3

-0.2

-0.1

0.1

f/fin

0.02 0.04 0.06 0.08 0.1

0.12 0.14 0.16 0.18 0.2

-0.5

-0.4

-0.3

-0.2

-0.1

0.1

0.2

0.3

0.4

0.5

FIR4

Sin(x)/x

Corrected

OUT DAC

0.05 0.1 0.15 0.2 0.25

0.3 0.35

0.4 0.45 0.5

-4

-3

-2

-1

FIR4

Corrected

Sin(x)/x

OUT DAC

DAC3282

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SLAS646A – DECEMBER 2009 – REVISED FEBRUARY 2010

The zero-IF sinc filter has a gain > 1 at all frequencies. Therefore, the input data must be reduced from full scale

to prevent saturation in the filter. The amount of back-off required depends on the signal frequency, and is set

such that at the signal frequencies the combination of the input signal and filter response is less than 1 (0 dB).

For example, if the signal input to FIR4 is at 0.1 × fDAC, the response of FIR4 is 0.1 dB, and the signal must be

backed off from full scale by 0.1 dB to avoid saturation.

The filter taps for all digital filters are listed in Table 5.

Note that the loss of signal amplitude may result in lower SNR due to decrease in signal amplitude.

Figure 37. Magnitude Spectrum for FIR0

Figure 38. FIR0 Transition Band

Figure 39. Magnitude Spectrum for Zero-IF Sinc

Figure 40. Correction Range of Zero-IF Sinc

Correction Filter up to 0.5 × fDAC

Correction Filter 0 to 0.2 × fDAC

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