Other first-order functions were also realized in that work. High impedance current output meant easy cascading within current-mode system, as was also demonstrated in compact quadrature oscillator applications proposed therein [12].The active element, DVCC, was treated as an analog block selleck chemical (linear) and its applications in digital (nonlinear) were not explored. A very novel work, where DVCC was shown to be not only tunable, but also good for some nonlinear applications [13] was next reported. DVCC’s X-terminal resistance was shown to be electronically tunable through the bias voltage of DVCC, so as to be used for a new voltage-controlled all-pass section. The pole-frequency tuning was demonstrated through the bias voltage.

The circuit [13] used two DVCCs and one grounded capacitor as the only passive component so as to fall in active-C category, with the feature of electronic tuning and low output impedance as well. An interesting and new application in four phase clock generation was also given, where the DVCCs were used as comparators for the first time. The concept was later popularized for complex neural circuits as well. Furthermore the research on tunable DVCC also got an impetus thereafter.Coming back to the active-RC circuits, a new topology was discovered, which produced six all-pass filters besides several other first-order simple analog blocks. Each all-pass circuit employed one DVCC withZ+ stage only and three passive components [14]. The work extended beyond first-order functions to second-order filters and third-order oscillators.

A true voltage mode work on all-pass filters presented one FDCCII and two components-based circuits with high input and low output impedances, and further demonstrated their utility for higher-order filters and oscillators [15]. The most recent update to the technical literature proposes a new active building block named dual-X current conveyor with buffered output and all-pass filters using this active building block. Four new circuits both use two or three passive elements and enjoy high input as well as low output impedance [16]. As compared to [15], the active element is simpler and hence economical. Moreover, high frequency potential of the new circuits makes them superior to other work [1�C15].3. A Novel Solution and ComparisonsThe preceding section presented a detailed look at notable first-order all-pass filters published during the last decade.

Picking the first and the latest reference shows some interesting revelations [1, 16]. The work based on CCII? [1] and the one with buffered output DXCCII Drug_discovery [16] shows a common feature of employing a floating capacitor. For comparison sake, out of the four circuits proposed in [16], the one closest to the first work [1] is chosen; it is Filter-4 of [16].