Comment On 'low Input Impedance Trans-impedance Type Multifunction Filterusing Only Active Elements'

摘要

This comment relates to a recently published article, which presents a low input impedance trans-impedance type multifunction filter using only active elements. The proposed circuit uses two operational amplifiers (OAs) and four single-output operational transeonduc-tance amplifiers (OTAs). It is shown here that one of the OTAs is redundant and the lowpass, highpass and bandpass trans-impedance type realisations can be achieved using only three OTAs rather than four. The proposed circuit of Minaei, Topcti and Cicekoglu (2005), is shown in Figure l(a), for convenience. As mentioned by Minaei et al. (2005) OTA4 provides a zero input impedance if it is assumed ideal, as its inverting input voltage will be forced to be zero since its output current is forced to be zero.