| 摘要 |
<p>A noise masking circuit for eliminating evidence of noise present in an incoming alternating electrical control signal, such as a shaft encoder or tachometer signal in a servo control circuit, is disclosed. A timer is started in response to a negative-going excursion in the incoming alternating electrical control signal. A first logic state output (low state) is produced by the timer in response to the negative-going excursion during a preselected period of time irrespective of the appearance of positive-going excursions which appear in the control signal. The timer is stopped after the preselected time period following the appearance of the negative-going excursion. Subsequently, that is, after the lapse the preselected time period following the initial appearance of the negative-going excursion, a second logic state output (high state) is produced by the timer in response to a positive-going excursion. Preferably, the timing means is restarted in response to the positive-going excursion. A second logic state output (high state) is produced by the timer in response to the positive-going excursion during a second preselected period of time irrespective of the appearance of negative-going excursions which appear in the control signal during the second preselected time period. The timer is stopped after the second preselected time period following the appearance of the positive-going excursion. Subsequently, that is, after the second preselected time period, a first logic state output (low state) is produced by the timer in response to a negative-going excursion. Other features are also disclosed.</p> |
