Elsewhere in this collection of small circuits, a 1-dB version of a third-order Chebyshev filter can be found. This 3-dB version is a bit steeper after the corner frequency. The inherent disadvantages are the increased ripple in the pass-band and more ringing in response to a square wave. The indicated frequency is the corner frequency at –3 dB. This time as well, two tables are printed here.
Table 1 shows an implementation with three equal resistors for the filter section and the theoretical values for the capacitors. In the case of a high-pass filter, three equal capacitors can be used. The resulting ‘oddball’ values can be synthesized by combining values from the E96 range. Table 2 indicates more practical values for the filter section, by selecting E12 values for the capacitors and theoretical values for the resistors (which can be built by combining 1% components). It is best to use a very fast opamp so that the transfer function is not unduly influenced, particularly with higher gains or at higher frequencies.