Study of practical problems in two-loop CCTA based biquad: Finite attenuations in stop bands

Quite neglected and underlying problem of modern active functional blocks is presented and demonstrated in this contribution on a current-mode active filter. The discussed problem is an undesirable transfer in stop band of multifunctional frequency filters. It is caused by several occasions related to small-signal parameters of active elements (impedance levels) in the circuit. In some cases it leads to parasitic feedback and undesirable transfers in circuit. Problems are discussed on example with KHN-type filter where quite novel active element known as Current Conveyor Transconductance Amplifier (CCTA) is used.