LM90

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SNIS126A – MAY 2004 – REVISED MARCH 2013

DIGITAL FILTER

In order to suppress erroneous remote temperature readings due to noise, the LM90 incorporates a user-

configured digital filter. The filter is accessed in the FILTER and ALERT CONFIGURE REGISTER at BFh. The

filter can be set according to the following table.

D2

D1

Filter

0

0

No Filter

0

1

Level 1

1

0

Level 1

1

1

Level 2

Level 2 sets maximum filtering.

Figure 12 depict the filter output to in response to a step input and an impulse input. Figure 13 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.

Filter Output Response to a Step Input

Figure 11. a) Step Response

Figure 12. b) Impulse Response

The filter on and off curves were purposely offset to better show noise performance.

Figure 13. Digital Filter Response in a Pentium 4 processor System

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