Patent ID: 6989692
Filing Date: 2006-01-24
Classification: H03K

Abstract:
1. A voltage sensor circuit comprising: a source-input node having a source-input voltage that is varied by a voltage source, the voltage sensor circuit sensing the source-input voltage of the source-input node; a stable node having a stable voltage that is relatively insensitive to changes in a supply voltage; a first current source, responsive to the source-input voltage, for generating a first current from the stable node that varies with variations in the source-input voltage; a first resistor, coupled to the first current source and receiving the first current, for generating a compare-input voltage on a compare-input node in response to the first current, the compare-input voltage varying with variations in the first current; a second current source for generating a second current that is insensitive to variations in the source-input voltage; a second resistor, coupled to the second current source and receiving the second current, for generating a reference voltage on a reference node in response to the second current; and a comparator coupled to the compare-input node and the reference node, for comparing the compare-input voltage to the reference voltage and generating an output voltage at an output node that indicates when the compare-input voltage is above the reference voltage; wherein the first current source is a substrate-sensing transistor having a substrate node driven by the source-input voltage and a gate driven by a constant bias voltage, the substrate-sensing transistor conducting the first current between the stable node and the compare-input node, wherein the first current through the substrate-sensing transistor varies with variations in voltage.