Page 248 - Op Amps Design, Applications, and Troubleshooting
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230    ACTIVE FILTERS


               analytical method assumes that the filter was designed according to standard prac-
               tices. The checks below will provide you with a reasonable degree of assurance that
               the filter design is compatible with the analytical procedure to be described:

                  1. Is K 3 approximately twice the size of RI?
                  2. Are Q and C 2 equal in value?
                  3. Is RI at least 10 times the size of R 2?


               If the answer is yes to all of these questions (which is the typical case), then the filter
               can be analyzed as described below. We will compute the following characteristics:

                  1. Resonant frequency
                  2. Q
                  3. Bandwidth
                  4. Voltage gain

               Filter Q. The Q of the filter shown in Figure 5.12 can be computed with the fol-
               lowing equation:








               Substituting values gives us







               Since the Q is less than 10, we will classify this circuit as a wide-band filter.

               Resonant Frequency. The resonant frequency of the filter shown in Figure
               5.12 can be computed with the following equation:








               where C is the value of either Q or C 2. Calculations for the present circuit are






               It is this frequency that should receive the most amplification (or least attenuation)
               from the filter circuit.
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