CFOA-based single resistance controlled quadrature oscillator

Identification of a class of two CFOA-based sinusoidal RC oscillators

“…Over the years, a number of schemes have been developed for realizing sinusoidal oscillators using various active elements; for example the operational amplifier (OA), the operational transconductance amplifier (OTA) and the current-feedback operational-amplifier (CFOA). Of particular interest here are the two-CFOA-based sinusoidal oscillators [1][2][3][4][5][6][7][8][9][10][11]. This is attributed to the following attractive features of the CFOA: high slew rate, flexible gain-bandwidth product; thus a constant bandwidth can be achieved over a wide range of closed loop gain and high operational frequency range.…”

“…This is attributed to the following attractive features of the CFOA: high slew rate, flexible gain-bandwidth product; thus a constant bandwidth can be achieved over a wide range of closed loop gain and high operational frequency range. However, many of the papers available on this subject, with few exceptions, are either concerned with one new circuit in each paper [1,3,5,8,9] or presenting a number of circuits without showing how these circuits were obtained [10]. This is because these circuits were discovered either by accident or with the help of intuition and various hit-and-miss techniques.…”

“…In the circuits reported in [1,3] a floating capacitor and a floating resistor are used. While the floating resistor is connected to terminal x of the CFOA, and therefore can absorb the parasitic resistance, r x , at this terminal, the capacitor is not grounded and cannot absorb the parasitic capacitances at the z terminal of the CFOA.…”

“…Apart from the obvious advantage of unifying the analysis of this class of oscillators, this treatment leads to the systematic discovery of numerous new two-CFOA-based oscillators; some of them have interesting new features. On the other hand, the condition of startup and the frequency of oscillation of the circuits proposed in [1][2][3][4][5][6][7][8][9][10][11] are obtained by applying the Barkhausen criterion. Recently the use of this criterion for determination of the startup condition of oscillation has been challenged [13][14][15][16][17] and its failure has been reported.…”

Condition of phase angle for a new VDGA-based multiphase variable phase shift oscillator from 0^o to 90^o

“…Multiphase sinusoidal oscillators find applications in signal processing, instrumentation, measurement, communication and control systems [1][2][3][4][5][6][7]. Depending on the phase shift between the phases, the multiphase oscillator circuits are available in different angles [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. All these generators are specified with fixed phase shift angles like the phase shifter.…”