Not Recommended for New Designs

LMF100

SNOSBG9B – JULY 1999 – REVISED JUNE 2015

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9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

The LMF100 is a general purpose dual second-order state variable filter whose center frequency is proportional

summarized in Table 2.

Table 2. Clocking Options

POWER SUPPLY

CLOCK LEVELS

LSh

+

−5 V and +5 V

TTL (0 V to 5 V)

0 V

+5 V

−5 V and +5 V

CMOS (

−5 V to +5 V)

0 V

+5 V

0 V and 10 V

TTL (0 V to 5 V)

0 V

+10 V

0 V and 10 V

CMOS (0 V to 10 V)

+5 V

+10 V

−2.5 V and +2.5 V

CMOS

0 V

+2.5 V

0 V and 5 V

(

−2.5 V to +2.5 V) TTL (0 V to 5 V)

0 V

0 V

0 V and 5 V

CMOS (0 V to 5 V)

+2.5 V

+5 V

altered by external resistors as in Figure 43 through Figure 49. This is useful when high-order filters (greater than

two) are to be realized by cascading the second-order sections. This allows each stage to be stagger tuned while

using only one clock. The filter Q and gain are set by external resistor ratios.

All of the five second-order filter types can be built using either section of the LMF100. These are illustrated in

Figure 25 through Figure 33 along with their transfer functions and some related equations. Figure 35 shows the

effect of Q on the shapes of these curves.

9.2 Typical Application

When designing a LP filter that has similar pass band characteristic as a Butterworth topology but requiring a

much steeper roll off then a fourth-order Chebyshev topology can implement the need with one LMF100.

Figure 53. Implement a Fourth-Order Chebyshev LP Filter Having a 1-kHz Cutoff Frequency and 1-dB PB

Ripple With an LMF100

24

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