Filter Design in Thirty Seconds. . . continued

Appendix A ı Standard Resistor and Capacitor Values

E-12 Resistor / Capacitor Values
1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, and 8.2; multiplied by the decade value.

E-24 Resistor / Capacitor Values
1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5,
8.2, and 9.1; multiplied by the decade value.

E-96 Resistor Values
1.00, 1.02, 1.05, 1.07, 1.10, 1.13, 1.15, 1.18, 1.21, 1.24, 1.27, 1.30, 1.33, 1.37, 1.40, 1.43, 1.47,
1.50, 1.54, 1.58, 1.62, 1.65, 1.69, 1.74, 1.78, 1.82, 1.87, 1.91, 1.96, 2.00, 2.05, 2.10, 2.15, 2.21,
2.26, 2.32, 2.37, 2.43, 2.49, 2.55, 2.61, 2.67, 2.74, 2.80, 2.87, 2.94, 3.01, 3.09, 3.16, 3,24, 3.32,
3.40, 3,48, 3.57, 3.65, 3.74, 3.83, 3.92, 4.02, 4.12, 4.22, 4,32, 4.42, 4,53, 4.64, 4.75, 4.87, 4.99,
5.11, 5.23, 5.36, 5.49, 5.62, 5.76, 5.90, 6.04, 6.19, 6.34, 6.49, 6.65, 6.81, 6.98, 7.15, 7.32, 7.50,
7.68, 7.87, 8.06, 8.25, 8.45, 8.66, 8.87, 9.09, 9.31, 9.53, 9.76; multiplied by the decade value.

Appendix B ı Filter Notes (for the More Technically Minded)

Low Pass Filter
The filter selected is a unity gain Sallen Key Filter, with a Butterworth response characteristic. Numerous articles and books have been written describing this topology.

High Pass Filter
The filter selected is a unity gain Sallen Key Filter, with a Butterworth response characteristic. Numerous articles and books have been written describing this topology.

Narrow Band Pass Filter
The filter selected is a modified Deliyannis Filter. The Q is set at 10, which also locks the gain at 10, as the two are related by the expression:

A higher Q was not selected, because the op amp gain bandwidth product can be easily reached, even with a gain of 20 dB. At least 40 dB of headroom should be allowed above the center frequency peak. The op amp slew rate should also be sufficient to allow the waveform at the center frequency to swing to the amplitude required.

Wide Band Pass Filter
This is nothing more than cascaded Sallen Key high pass and low pass filters. The high pass comes first, so energy from it that stretches to infinite frequency will be low passed.

Notch Filter
This is the Fliege Filter topology, set to a Q of 10. The Q can be adjusted independently from the center frequency by changing R1 and R2. Q is related to the center frequency set resistor by the following:

The Fliege Filter topology has a fixed gain of 1.

The only real possibility of a problem is the common mode range of the bottom amplifier in the single supply case.

Band Reject Filter
This is nothing more than summed Sallen Key high pass and low pass filters. They cannot be cascaded, because their responses do not overlap as in the wide band pass filter case.

Author bio:
Bruce Carter is a Senior Applications Engineer at Texas Instruments. He authors books, magazine articles and applications notes, and gives seminars across the country on analog design using high speed op amps. He also assists customers who have difficult application problems. Mr. Carter is a 1978 graduate of Texas Tech University in Engineering Physics, and a 1979 graduate of the University of Texas in Electrical Engineering.

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