%0 Journal Article
%T Synthesis of New Single CFOA-Based VCOs Incorporating the Voltage Summing Property of Analog Multipliers
%A S. S. Gupta
%A D. R. Bhaskar
%A R. Senani
%J ISRN Electronics
%D 2012
%R 10.5402/2012/463680
%X Recently, current feedback operational amplifier (CFOA) and analog multiplier-(AM-) based-voltage controlled oscillators (VCOs) have been published in the literature which require 2ˋCFOAs and 2ˋAMs for linear tuning law between control voltage and frequency of oscillation. In this paper, a family of eight new voltage-controlled oscillators (VCOs), with linear tuning laws, employing only a single CFOA in conjunction with two analog multipliers (AMs), has been derived through a systematic state-variable methodology. This has been made possible by exploiting the voltage summing property of the multiplier chosen which has never been done in the literature earlier. The workability of the presented VCOs has been verified by experimental results based on AD844 type CFOAs and AD534 type AMs, and the advantages of new circuits over the previously known CFOA-AM-based VCOs have been highlighted. 1. Introduction Although a number of new building blocks and concepts related to current-mode circuits have been investigated in the literature [1每3], the use of current feedback operational amplifiers (CFOAs) as an alternative to the traditional voltage-mode op-amps (VOAs) has attracted considerable attention (see [4每7] and the references cited therein) in various instrumentation, signal processing, and signal generation applications due to their commercial availability as off-the-shelf ICs as well as due to the well-known advantages offered by CFOAs over the VOAs [4每6]. Because of these reasons, the use of CFOAs has been extensively investigated in realizing oscillators, for instance, see [6, 8每11] and the references cited therein. Although a variety of CFOAs are available from various manufacturers, AD844 (from Analog Devices), which contains a CCII+ followed by a voltage buffer is particularly flexible and popular due to the availability of -terminal of the CCII+ therein as an externally accessible lead which permits AD844 to be used as a CCII+ (one AD844) or as CCII-(realizable with two AD844s) or as a general 4-terminal building block [6]. This paper is concerned with the use of CFOAs in the realization of voltage-controlled oscillators (VCOs) which are required in several instrumentation, electronic, and communication systems, such as in function generators, in production of electronic music to generate variable tones, in phase locked loops, and in frequency synthesizers [12每17]. Although, recently, the use of CFOAs in the realization of linear VCOs has been reported in [7, 11], in this paper, the voltage summing property of the commercially available analog
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