Processor interface for electromechanical telephone exchange - contains matching circuits for analogue signals with comparators driving tri-state logic output stages

摘要

A number of interface circuits receive analogue inputs from various points in a telephone exchange. The interfaces convert and process the signals into digital signals for a processor. Each interface contains matching circuits for a number of parallel inputs. The input signal levels are converted to lower levels defined by voltage limit values. Multiplexers select the signals for threshold comparators controlled from a threshold level selector to provide calibration of the signal levels. The comparator outputs are applied to tristate logic circuits controlled from control circuits for input to the processor. A peak voltage selector comprising a multiplexer circuit enables the voltage limit values to be selected for the various matching circuits. Operational amplifiers reduce the effects of stray capacitances and reduce the settling time for the voltage values.