Abstract
Two topologies of operational transresistance (OTRA) based third order quadrature oscillators (QO) are proposed in this paper. The proposed oscillators are designed using a combination of lossy and lossless integrators. The proposed topologies can be made fully integrated by implementing the resistors using matched transistors operating in linear region, which also facilitates electronic tuning of oscillation frequency. The nonideality analysis of the circuit is also given and for high frequency applications self-compensation can be used. Workability of the proposed QOs is verified through PSPICE simulations using 0.5 μm AGILENT CMOS process parameters. The total harmonic distortion (THD) for both the QO designs is found to be less than 1%.
Highlights
Quadrature oscillators (QO) produce outputs having a phase difference of 90∘
Both the QO topologies are designed for an frequency of oscillation (FO) of 159 KHz and the simulated value was observed to be 161 KHz for Circuits I and II, respectively
The simulated transient output and corresponding frequency spectrum for Circuit I are shown in Figures 8 and 9, respectively, and those for Circuit II are depicted in Figures 10 and 11
Summary
Quadrature oscillators (QO) produce outputs having a phase difference of 90∘. The phase-locked sine-cosine relationship of QO has useful applications in the field of telecommunications where the modulation scheme utilizes both inphase and quadrature components, such as single-sideband generators and quadrature mixers [1]. The QOs are used extensively in the field of instrumentation and power electronics [2] For these applications low value of total harmonic distortion (THD) is an essential requirement as higher harmonics have detrimental effects on electrical equipment. A careful observation suggests that the reported QO designs are based on forming closed loop using (i) two lossy and one lossless integrators [3,4,5], (ii) one lossy and two lossless integrators [8], (iii) a second order low pass filter followed by an integrator [1, 6, 7, 10,11,12,13,14,15,16], and (iv) three low pass filters and gained feedback around the loop [9]. The proposed structures can be made fully integrated by implementing the resistors using matched transistors operating in linear region and can be tuned electronically
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