| 摘要 |
<p>A microprocessor or other digital logic circuit recurrently tests the logical switching state of an input port. Based upon the outcome of such testing, the logical switching state at an output port is switched to the state opposite that of the input port. The recurrent testing develops at the output port a rectangular wave voltage that switches between upper and lower voltage levels. A filter coupled between the two ports develops at the input port a voltage representative of the average value of the output port voltage. The recurrent testing of the logical switching state of the input port produces a negative feedback of the output port voltage to the input pork. The negative feedback develops a pulse-width modulated voltage at the output port that has an average value that is a multiple of the logic threshold voltage level of the digital logic circuit. To enable the digital logic circuit to perform a comparison of an analog voltage with a DC reference voltage, a second, comparison input port is coupled to the output port and is biased by the output port voltage at the logic threshold voltage level. The analog voltage and the DC reference voltage are then applied to the comparison input port. When the analog voltage exceeds the reference voltage, the voltage at the comparison port exceeds the logic threshold voltage level, resulting in the port being in a first logical switching state, and when the analog voltage is below the reference voltage, the voltage at the comparison port is below the logic threshold voltage level resulting in the input port being in the other logical switching state.</p> |
