| 摘要 |
A method and a circuit for producing a fail-safe output signal in case of an open circuit condition of an input pad of a digital circuit unit, comprising a first inverter stage ( 10, 18 ) providing a constant switch level; a second inverter stage ( 32, 44 ) providing a variable switch level that depends of the signal level of the input pad ( 28 ) and comparing the constant switch level of the first inverter stage ( 10, 18 ) with the variable switch level of the second stage ( 32, 44 ) and providing an output signal at an output terminal ( 42 ) thereof if the variable switch level of the second stage ( 32, 44 ) is greater than the constant switch level; and an additional circuit element ( 52 ) connected in series with the second inverter ( 32, 44 ) for decreasing the switch level of the second inverter stage ( 32, 44 ).
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