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Cascaded_IC_low_pass_filters

2017-02-18 20:07  
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Cascaded_IC_low_pass_filters
Figure 7-15A shows two LTC1062 filters where the second input is taken directly from the dc-accurate output of the first filter. The recommended ratio of R'/R is about 117/1, 1/(6.28RC) should equal fc/1.57, and 1/(6.28R'C') should equal fc/1.6 when the filters are cascaded (Fig. 7-15A). For example, for an fc of 4.16 kHz, the clock should be 416 kHz, and R=909 Ω, R'=107 kΩ, C=0.066 pF, and C'=574 pF. Figure 7-15B shows cascaded filters where the second input is taken from the buffered output of the first filter. The recommended values for R and C are determined by: 1/(6.28RC) =fc/1.59 and 1/(6.28R'C')=fc/1.64 when the filters are cascaded as shown in Fig. 7-15B. For example, for an fc of 4kHz, the values should be: R=97.6 kΩ, C=616 pF, R'=124 kΩ, and C'=508 pF. Linear Technology Corporation, Linear Applications Handbook, 1990, p. AN20-7.