Erasto M. (Erasto Muganyizi) Kashoro
Published: 1982
Total Pages: 0
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A sinusoidal RC-oscillator built around a current-controlled current amplifier is presented. Three main problems associated with RC-oscillators, namely poor frequency performance, amplitude drift and a large temperature coefficient of frequency, are addressed, and ways of solving these problems are discussed. The large temperature sensitivities typical of active RC networks were reduced by eliminating the active portion of the drift. This was accomplished through the use of thermally balanced amplifiers whose operation is independent of transistor parameters. It is shown that the frequency performance of a typical Wien-oscillator is significantly improved when fast current amplifiers are used to replace commercial voltage operational amplifiers. The generation of a sinusoidal signal directly from the oscillator gave a lower total harmonic distortion (THD) than in the more popular approaches using multivibrators and shaping networks. A new method for stabilizing the amplitude of oscillation has been developed. It employs a high frequency rectifier and a comparator in a feedback loop which is connected to the RC network of the oscillator through an active current divider. The feedback loop regulates the current in the RC network and thereby stabilizes the amplitude. A linear automatic gain control (AGC) model was developed and the stability requirements for the amplitude control loop were studied. Frequency stabilization for oscillators is a very difficult task. Most communication systems requiring tight frequency stability incorporate frequency synthesizers which have a large IC count and are expensive.