Patent ID: 6940318
Filing Date: 2005-09-06
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 first current source, responsive to the source-input voltage, for generating a first current 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, the reference voltage varying with variations in the second current; a stable node, coupled to the first current source and coupled to the second current source, the stable node having a stable voltage that is relatively insensitive to changes in a supply voltage; 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 comprises: a first mirror transistor having a channel that conducts the first current between the stable node and the compare-input node in response to a first gate node; a first setting transistor, with a gate connected to the first gate node, having a channel that conducts a first setting current between the stable node and the first gate node; a first sensing transistor having a channel that conducts a portion of the first setting current from the first gate node, the first sensing transistor having a gate connected to the source-input voltage; wherein the second current source comprises: a second mirror transistor having a channel that conducts the second current between the stable node and the reference node in response to a second gate node; a second setting transistor, with a gate connected to the second gate node, having a channel that conducts a second setting current between the stable node and the second gate node; and a second sensing transistor having a channel that conducts a portion of the second setting current from the second gate node, the second sensing transistor having a gate connected to a fixed voltage.