Analogue computing circuit for quarz oscillator - noise problems associated with small amplitude input by using comparator controlled stage

摘要

An analogue control circuit for the determination of the characteristic of a quartz oscillator performs either multiplication or division of two A.C. signals followed by multiplication or division by a constant. The solution provides a greater dynamic operational range, high computing speed and accuracy particularly in the situation where one input is of a very much smaller amplitude than the other. The larger amplitude input (A) is amplified (1) and the R.M.S. value generated by a rectifier (2) before the logarithmic function is generated (3). Signal (B) is transmitted through a similar arrangement except the rectifier (6) and a second amplifier are controlled by a comparator stage (8). The comparator ensures a constant gain factor through the second stage amplifier and rectifier and avoids any problem due to noise. The logarithmic output (9) is compared with Log A (10) to generate the required outputs (A/B.V, A.B.V.).