An improved circuit arrangement for detecting cross-over by an alternating voltage of a fixed reference voltage level

摘要

A circuit arrangement for detecting the crossings by an applied alternating voltage of two separate threshold levels respectiveiy above and below a fixed reference voltage level comprises: the series combination of two resistances(1 and 2) in an electrical path between the applied alternating voltage and the dc reference voltage which includes voltage comparators (VC1 and VC2) having two possible logic output states to compare the voltage at the junction (P) of the two resistances with the reference voltage (5) so that the logic output state of the comparators at any instant is determined by the voltage at the junction relative to the reference voltage, and logic means (G1) in which the logic output state of the comparators is combined so that a pulse spanning each instant of cross-over by the applied alternating voltage of the reference voltage is produced thereby having a leading edge and a trailing edge which respectively correspond with the instants of crossing by the applied alternating voltage of the two separate threshold levels. One threshold level is determined by the magnitude of the reference voltage (5) and the other threshold level is determined by the ratio of the resistance values of the two resistances (1 and 2) and the dc supply voltage. A circuit in which a resistor is replaced non-linear network is also described. This circuit is particularly fit for application in an integrated circuit.