New parallel-path biquad active-RC oscillators with enhanced frequency stability

Examination of several single- and multi-op amp active-RC oscillator designs has revealed that the open loop transfer function is either a second-order bandpass or biquadratic function. In all cases encountered, the frequency selectivity of the oscillator open loop transfer function was low, leading to poor frequency stability. However, it has been found possible, using a parallel-path technique, to realise an active-RC network having a biquadratic transfer function with a degree of frequency selectivity. It is therefore possible to design active-RC oscillators with considerably enhanced frequency stability when compared with traditional designs. This presentation will deal with the techniques employed in the design of such oscillators