TABLE OF CONTENTS Besides sensitivity, other means by which we can reduce the cost of the circuit is to reduce its size or the area on the chip (real estate) and simplify the fabrication process. By eliminating the capacitors, at least two for each second-order section, we have the potential for doing both. These capacitors, because of their high values (typically C ? 100 pF), are the most impractical values to fabricate in monolithic IC form and consume a substantial portion of the filter's chip area or real estate. Among the various methods that have been proposed for the implementation of monolithic filters, active- R filters [P22-P24, P26] received early attention because they employ no capacitors other than the small capacitors used to internally compensate the op amps [see Eqs. (2-26)-(2-28)]. In addition, they are more suitable for operation at higher frequencies ( f 0 > 20 kHz) than are comparable active- RC filters. This may be their prime function as seen later in the section. In active- R circuits, the amplifiers are used as integrators and filter parameters, such as pole frequency ? 0, pole quality factor Q, and flat gain, are established by the GBs of the amplifiers and ratios of resistors. Since resistor ratios can be maintained to high precision with hybrid or monolithic technology, one is left with the task of finding a means to stabilize the amplifier GBs, both in manufacture...
