| 摘要 |
Apparatus for producing a signal, comprising a capacitor; a first current source for one of charging and discharging the capacitor over a first time period; a second current source for one of discharging and charging the capacitor over a first portion of a second time period; a detector for detecting when the voltage across the capacitor is substantially a first voltage and controlling the second current source for a second portion of the second time period to substantially maintain the voltage across the capacitor; and an apparatus output for indicating when the voltage across the capacitor is one of above and below the first voltage.
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