International Scholarly Research Notices

Volume 2015, Article ID 690923, 7 pages

http://dx.doi.org/10.1155/2015/690923

## Electronically Tunable Differential Integrator: Linear Voltage Controlled Quadrature Oscillator

^{1}Department of Electronics & Telecommunication Engineering, Jadavpur University, Kolkata 700032, India^{2}Department of Electronics & Communication Engineering, Narula Institute of Technology, Kolkata 700109, India^{3}Department of Electronics Engineering, B. P. P. Institute of Technology, Kolkata 700052, India

Received 15 December 2014; Revised 22 March 2015; Accepted 26 March 2015

Academic Editor: Stephan Gift

Copyright © 2015 Rabindranath Nandi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

A new electronically tunable differential integrator (ETDI) and its extension to voltage controlled quadrature oscillator (VCQO) design with linear tuning law are proposed; the active building block is a composite current feedback amplifier with recent multiplication mode current conveyor (MMCC) element. Recently utilization of two different kinds of active devices to form a composite building block is being considered since it yields a superior functional element suitable for improved quality circuit design. The integrator time constant and the oscillation frequency are tunable by the control voltage of the MMCC block. Analysis indicates negligible phase error for the integrator and low active -sensitivity relative to the device parasitic capacitances. Satisfactory experimental verifications on electronic tunability of some wave shaping applications by the integrator and a double-integrator feedback loop (DIFL) based sinusoid oscillator with linear variation range of 60 KHz~1.8 MHz at low THD of 2.1% are verified by both simulation and hardware tests.

#### 1. Introduction

Dual-input integrators with electronic tunability are useful functional components for numerous analog signal processing and waveforming applications [1]. A number of single and dual-input passive tuned integrators using various active building blocks are available [2, 3].

However, integrators with electronically adjustable time constant find some exclusive applications [4–6], for example, in electronically tunable biquadratic phase selective filter design [7], as electronic reset controller and phase compensator [8] for process control loops.

Quadrature sinusoid oscillators are widely used in orthogonal signal mixers, in PLLs and SSB modulators; some such oscillators based on various active devices, for example, voltage operational amplifier-VOA [9], CFOA [10, 11], CDBA [12, 13], CDTA [14], DDCC [15], CCCCTA [16], OTA [17], and DVCCTA [18, 19], are reported.

Here we present a simple electronically tunable dual-input integrator (ETDI) topology based on a composite current feedback amplifier- (CFA-) multiplication mode current conveyor (MMCC) building block. It has been pointed out in the recent literature [20, 21] that utilization of two different kinds of active elements to form a composite building block yields superior functional result in analog signal processing applications.

Hence the topic of quadrature sinusoidal oscillator design and implementation with better quality is receiving considerable research interest at present. A number of such oscillators using various active building blocks [9–17] are now available. Here, we present a new simple ETDI topology, based on a composite CFA-MMCC building block with grounded capacitor; subsequently, a double-integrator feedback loop (DIFL), with one inverting and the other noninverting, is utilized to design a linear VCQO wherein a pair of grounded -section selects the appropriate signal generation band and the control voltage of the MMCC tunes oscillation frequency linearly; no component matching constraint is involved here. This current conveyor element is quite an elegant building block with a dedicated control voltage terminal; hence the MMCC is a versatile active component suitable for electronically tunable function circuit design.

It is seen in recent literature that such linear VCQO is a useful functional block which finds wide range of applications in emerging fields; namely, in certain telemetry-related areas it could convert a transducer voltage to a proportional frequency which is then modulated for subsequent processing [22], as quantizer for frequency-to-digital or time-to-digital conversion [23] and also as the spectrum monitor receiver [24] in cognitive radio communication studies.

Here, we present the design and realization of a new linear VCQO using the composite type active device; analysis shows that device imperfections, namely, port tracking errors and parasitic capacitors at current source nodes, yield negligible effects on the nominal design, whereby the active-sensitivity figures are extremely low. Experimental measurements by simulation and hardware tests on the proposed design indicate satisfactory results with -tunability in the range 60 KHz–1.8 MHz following the variation of a suitable control voltage wherein a desired band-spread may be selected by appropriate choice of the grounded components [25], without any component matching constraint, even with nonideal devices.

#### 2. Analysis

The ETDI topology is shown in Figure 1(a); the nodal relations of the active blocks are , , , and for the CFA and , , , and for the MMCC where is multiplication constant [12] and is control voltage. The port transfer ratios (, , and ) are unity for ideal elements; the imperfections may be postulated in terms of some small error coefficients as , , and . Also, shunt- parasitic components appear [26–28] at the -node of the blocks having typical values in the range of and ; since resistance values used in the design are in KΩ ranges, their ratios to are extremely small and hence effects of are negligible in the design. It may also be mentioned that a low-value internal parasitic resistance appears in series with the current path at -node of the devices; its effect can be minimized by absorbing -value in the load resistors at these nodes. Routine analysis assuming yields the open-loop transfer in Figure 1(a) aswhere