
Tricks of the trade 307
the input of the second opamp in a h'\gh-Q
second-order vV-path filter section (see Figure
7.18). Figure 11.25a shows a circuit which provides
a ground referenced capacitance of -C, where C is
the value of the capacitor providing feedback
around the opamp. It is stable when connected in
parallel with a (positive) capacitance of value
greater than C. Figure 11.25b shows a centre
grounded negative capacitor. The slightly more
complex circuit of Figure 11.25c can provide a
floating (not ground referenced) negative capaci-
tance. The principle of operation of the circuits of
Figure 11.25 is not too difficult to grasp, an