Page 339 - Analog and Digital Filter Design
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336 Analog and Digital Filter Design
Integrated Circuit Filter UAF42
The Texas Instruments (Burr-Brown) UAF42 can be used to produce a low-
pass, highpass, bandpass, or bandstop active filter. All-pole frequency responses,
such as Bessel, Butterworth, and Chebyshev, as well as those responses with
a zero in the stopband, are possible, such as Inverse Chebyshev and Cauer
(Elliptic).
The UAF42 has a single second-order section comprising three op-amps and an
auxiliary op-amp. The auxiliary op-amp is useful for producing bandstop filters
or filter responses with a zero in the stopband, such as an Inverse Chebyshev
type. Each op-amp has a gain-bandwidth product of 4MHz and a slew rate of
lOVIps, which gives a useful range of passband operating frequencies of up to
100 kHz. The internal circuit schematic is given in Figure 14.1.
Figure 14.1
Circuit of UAF42
The UAF42 includes 50 kC2 resistors and 1 nF capacitors, but external resistors
are required to complete the design. However, because the UAF42 only contains
one second-order section, access to both ends of the internal resistors and capa-
citors is possible in this IC. This allows external components to be connected in
