From equation (2), if C1 = C2 and R2 = R3, one can ® nd that the resistive component
spread is low since it is only proportional to Q (Liu 1995b). Moreover, x 0 and Q
can be orthogonally adjustable. Once the JFET transistors are used to replace the
grounded resistors, R1 and R2, an electronically tunable ® lter can be obtained. In
fact, another universal ® lter can be obtained if the types of those two CCIIs in Fig. 1
are exchanged (i.e. CCII1= CCII+ and CCII2= CCII± ).