1.11 DIGITAL FILTER

D2

D1

Filter

0

0

No Filter

0

1

Level 1

1

0

Level 1

1

1

Level 2

In order to suppress erroneous remote temperature readings

due to noise, the LM99 incorporates a user-configured digital

filter. The filter is accessed in the FILTER and ALERT CON-

FIGURE REGISTER at BFh. The filter can be set according

to the table shown.

Level 2 sets maximum filtering.

Figure 8 depict the filter output to in response to a step input

and an impulse input. Figure 9 depicts the digital filter in use

in a Pentium 4 processor system. Note that the two curves,

with filter and without, have been purposely offset so that

both responses can be clearly seen. Inserting the filter does

not induce an offset as shown.

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a) Step Response

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b) Impulse Response

FIGURE 8. Filter Output Response to a Step Input

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FIGURE 9. Digital Filter Response in a Pentium 4 processor System. The filter on and off curves were purposely

offset to better show noise performance.

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