| 摘要 |
1,226,410. Threshold switching circuits. TELEFONAKTIEBOLAGET L. M. ERICSSON. 17 June, 1968 [15 June, 1967], No. 28833/68. Heading H3T. Hysteresis in a threshold switch is avoided by periodically resetting the switch to one of its states by chopping the input signal so that the switch is again set only if the signal still exceeds its threshold, the chopping being effected via a timing circuit from the output and being unaffected in duration by the amplitude of the signal. Fig. 6 shows a Schmitt trigger ST1 which switches over if the signal applies to the first base exceeds the set threshold level. Such switching operates a monostable multivibrator MV1 the output of which is differentiated so that the trailing edge renders a chopper transistor 51 conducting and so resets the Schmitt trigger. The output from the Schmitt trigger and from the monostable multivibrator therefore consists of pulses which are repeated until the signal drops below the set threshold level of the trigger. The output from the monostable multivibrator is fed to a circuit MV3 which switches its state in response to the first pulse and remains there so long as the pulses continue so that an output is available from 70 so long as the signal is above the threshold. A second similar circuit ST2, MV2, MV4, 80 operates if the signal goes below a second threshold, the trigger circuit in this case being reset to its other threshold by a transistor such as 51 connected between the base and the collector supply. In Fig. 4 (not shown) it is suggested that the circuit corresponding to MV3 could be a monostable multivibrator which remains in its unstable state so long as triggering continues and that a similar multivibrator could be connected to the output of MV1, the output of the circuit being taken from either side of the output multivibrators depending on the sense of the signal required. |
