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By MUHAMMAD TAHER ABUELMA'ATTI and NOURIA ABDULLAH HUMOOD Connecting opamps for unity gain increases oscillator frequency by minimizing gainbandwidth product restrictions. In 1985, Senani* proposed a new sinusoidal oscillator based on unitygain opamp configurations. Compared with oscillators using opamps as finite or infinitegain voltagecontrolled voltage sources, this new approach produces circuits that work at much higher frequencies. Consider the five configurations of Fig. 1. Assuming ideal unitygain amplifiers, routine analysis yields the characteristic equations of the circuits which are, respectively, By performing all possible permutations of these five configurations, two oscillator circuits result from each configuration, Fig. 2. Oscillation conditions and frequency equations for each circuit are summarized in Table 1. Sensitivity is calculated using. where ω0 is the oscillationfrequency parameter and y is the element of variation. From Table 2 it is clear that the ten oscillators have low sensitivity characteristics. Results are presented for only four of the oscillator circuits, Figs 36. but all ten designs have been built and tested using 741 opamps. Good quality oscillations have been successfully produced and sustained at up to approximately 295kHz. Each of the ten new activeRC oscillators shown uses two opamps connected for unity gain, three capacitors and three resistors. Connecting the opamps for unity gain minimizes the effects of gainbandwidth product, so higher oscillation frequencies are easily obtained. All ten circuits have low sensitivity characteristics.  Muhammad Abuelma'atti and Nouria Humood are with the Department of Electrical Engineering and Computer Science at the University of Bahrain. Senani. R.. New RC active oscillator configuration employing unitygain amplifiers. Electronics Letters. Vol. 21. pp. 889891. 
Fig. 4. Oscillation frequency versus capacitance C3 for the circuit of Fig. 2(e). Resistor R1=1/G1=1.8kohm, R4= 1/G4= 900 ohm, R6=1/ GE = 200 ohm, C2 = 100pF and C5= 5nF. Fig. 5. Varying C4 in Fig. 2(g) gives this frequency curve for R1 =1/G1166 ohm. R2= 1/G2 = 200 ohm, R6= 1/G6= 112k ohm, C3= 10nF and C5= 1nF. Fig. 6. With the circuit of Fig. 2(i), varying C4 results in this frequency curve. Resistor R1=1/G1=289 ohm. R31/G3= 300 ohm, R6=1/ G6 17.7kohm, and C2= C5=1nF. ========== (adapted from: Wireless World , Oct. 1987)

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