Telephone multifrequency switching signals detection - uses analysis circuits with filter outputs counted during enabling period

摘要

Multifrequency signals employed in telephonic telecommunications switching are detected using two analysis circuits for all the components of a multifrequency code of the 2 from n type. This method overcomes difficulties experienced with tuned filters in parallel. Two analysis circuits are connected in parallel to a telephonic line (L). One circuit contains a high pass filter (PH) while the other contains a low pass filter (PB) both comprising operational amplifier circuits with RC networks. The filter outputs are amplified (A1, A2) to obtain square waves for application to counters (CR1, CR2) which count during a time period determined from an enabling input (K). The counter outputs (S1, S2) therefore depend on the frequency inputs.