Posted on Jun 4, 2012 11366
Cascading two identical integrators will thus result in an overall phase shift of 180Â° and an amplification of unity (p
rovided that the frequency is 1/2kRiCi): an ideal basis for an oscillator. The two integrators are connected in the feedback circuit of an amplifier whose gain is determined by the amplitude of the output signal. Consequently, the generator has reasonably stable output voltage (at a level of about 4.5 Vpp). The frequency of the generator is determined by integrators IC1B and IC1C. An integrator has two properties that are used in this design. Firstly, a phase shift of 90Â° is between the input and output (ignoring, for the moment, the nonideal behavior of the op amp), and secondly, its amplification is -1. With the values of CI (CI") and RI (RI"), as shown in the diagram, the output has a frequency of about 300 Hz. The frequency can be varied by replacing RI and RI" with a stereo potentiometer. To keep the frequency setting within bounds, the overall range of this potentiometer should not exceed a decade. The maximum attainable frequency is about 5 kHz. Distortion is not greater than 0.1%. The current drawn by the generator is only a few milliamperes. Finally, the LM348 is a quadruple 741; it is thus possible to construct the generator from four 741s.