Method and apparatus for producing a trigger signal

摘要

An apparatus is provided for producing a trigger signal in accordance with the occurrence of an event, for example the end of the last pulse of a train of pulses, which occurs in an almost periodic manner within periodically consecutive time intervals and having a specific distinguishing feature relative to the remainder of the events occurring within each of said time intervals. The apparatus comprises a signal examination and time measurement circuit (3) which receives a signal on a rail (2) which represents the events and which determines the occurrence time of the event having the distinguishing feature. The output of the circuit (3) is provided to a holding circuit (6) which is controlled by a clock signal and which has its output connected to a signal modification circuit (8) which modifies the output signal of the circuit (6) so that it represents a slightly earlier time. The output of the circuit (8) is connected to the input of an enabling signal generator (9) which is responsive to an output signal of the circuit (3) and which produces an enabling signal on a rail (11) shortly before the event having the specific distinguishing feature occurs. The enabling signal is provided to one input of a signal combining circuit (12), the other input of which receives the signals provided on the rail (2) and at the output of which there is provided the trigger signal.