Page 149 - The Master Handbook Of Acoustics

124 CHAPTER SIX

resistors on a semiconductor wafer and interconnecting the compo-
nents by an evaporated metal pattern. Great circuit complexity can
be compressed into unbelievably small space in this way.
A low-pass filter assembled from inductors and capacitors in the
old-fashioned way is shown in Fig. 6-6A. Another low-pass filter
based in an integrated circuit is shown in Fig. 6-6B. The four small
resistors and two small capacitors plus the integrated circuit illustrate
the space-saving advantage of the active filter.
It is interesting that the feedback capacitor C 1 in Fig. 6-6B has the
electrical effect of an inductance.

Analog vs. Digital Filters
Filters can be constructed in analog or digital form. All the filters dis-
cussed to this point have been of the analog type and applied widely in
equalizers. By adjusting the values of the resistors, inductors, and capac-
itors any type of analog filter can be constructed to achieve almost any
frequency and impedance matching characteristic desired.

A

C 1

B
FIGURE 6-6
Two low-pass filters, (A) traditional analog type, (B) an active filter utilizing an inte-
grated circuit.