Abstract
A linear voltage controlled quadrature oscillator implemented from a first-order electronically tunable all-pass filter (ETAF) is presented. The active element is commercially available current feedback amplifier (AD844) in conjunction with the relatively new Multiplication Mode Current Conveyor (MMCC) device. Electronic tunability is obtained by the control node voltage (V) of the MMCC. Effects of the device nonidealities, namely, the parasitic capacitors and the roll-off poles of the port-transfer ratios of the device, are shown to be negligible, even though the usable high-frequency ranges are constrained by these imperfections. Subsequently the filter is looped with an electronically tunable integrator (ETI) to implement the quadrature oscillator (QO). Experimental responses on the voltage tunable phase of the filter and the linear-tuning law of the quadrature oscillator up to 9.9 MHz at low THD are verified by simulation and hardware tests.
Highlights
Realization of first-order all-pass filters had been reported earlier using various types of active building blocks (ABBs), namely, VOA [1], Current Conveyor and its variants [2,3,4,5], DDA [6], DDCC [7], DVCC [8, 9], VDIBA [10], and OTA, with differential amplifier [11] as listed in Table 1; some of these building blocks are implemented with a basic device (OTA, CC, or DVCC) combined with some signal differential unit
Recent literature suggests that electronic function circuits fabricated by commercially available IC modules are capable of providing desired results [12,13,14,15,16]
We present here an electronically tunable all-pass filter (ETAF) using the composite CFA-Multiplication Mode Current Conveyor (MMCC) block
Summary
Realization of first-order all-pass filters had been reported earlier using various types of active building blocks (ABBs), namely, VOA [1], Current Conveyor and its variants [2,3,4,5], DDA [6], DDCC [7], DVCC [8, 9], VDIBA [10], and OTA, with differential amplifier [11] as listed in Table 1; some of these building blocks are implemented with a basic device (OTA, CC, or DVCC) combined with some signal (current or voltage) differential unit. Recent literature suggests that electronic function circuits fabricated by commercially available IC modules are capable of providing desired results [12,13,14,15,16]. Some recent composite blocks yield quite useful results on signal processing applications wherein two types of basic commercially available chips are conjoined (e.g., DDCC, DVCC, and VDIBA). It has been suggested that composite blocks may provide better results in comparison to the constituent elements [17] For such ABBs requiring more than one commercially available IC, it is still economical and more convenient compared to chip fabrication [12, 16, 17]. Experimental results on ETAF and quadrature oscillator responses are verified by PSPICE simulation and hardware test
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