Abstract In a selective calling circuit including a band-pass filter which may be constituted by an active filter, and a power source for energizing the filter, a control signal is generated which has a predetermined duration in accordance with the output of the band-pass filter at a point of time whereat the output of the band-pass filter reaches a predetermined level. In response to the control signal, there is established a state in which the center frequency of the band-pass filter can be changed, and the output of the power source is changed from a first level to a second level for a period of time substantially corresponding to the predetermined duration of the control signal. At the aforementioned first level, the band-pass filter may be energized, while at the second level, it may be deenergized.
A selective calling circuit including band-pass filter means having its center frequency changeable so as to sequentially pass therethrough a plurality of tone signals arriving in succession in accordance with a predetermined code and power source means for energizing said band-pass filter means, the improvement comprising means for generating a control signal having a predetermined duration in accordance with the output of said band-pass filter means at a point of time whereat said output reaches a predetermined level, and means responsive to said control signal to establish a state in which the center frequency of said band-pass filter means can be changed and to change the output of said power source means from a first level whereat said band-pass filter means may be energized to a second level whereat said band-pass filter means may be deenergized, for a period of time substantially corresponding to said predetermined duration of said control signal.
Claim 2
Dependent Claim
151 words
A selective calling circuit including band-pass filter means having its center frequency changeable so as to sequentially pass therethrough a plurality of tone signals arriving in succession in accordance with a predetermined code and power source means for energizing said band-pass filter means, the improvement comprising means for generating a control signal having a predetermined duration in accordance with the output of said band-pass filter means at a point of time whereat said output reaches a predetermined level, and means responsive to said control signal to establish a state in which the center frequency of said band-pass filter means can be changed and to change the output of said power source means from a first level whereat said band-pass filter means may be energized to a second level whereat said band-pass filter means may be deenergized, for a period of time substantially corresponding to said predetermined duration of said control signal.
Claim 3
Dependent Claim
17 words
A selective calling circuit according to claim 1, wherein said band-pass filter means comprises an active filter.