Power-on detect by measuring thermal voltage
AssigneeNational Semiconductor Corporation
InventorPerry Scott Lorenz
Life of this patent
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Abstract
A power-on detection circuit is arranged to cooperate with a thermal-voltage generator to determine when predictable circuit operation is achieved. The power-on detection circuit includes a comparator circuit and an inverter circuit. A power-on reset (POR) signal is generated by the inverter circuit, which evaluate an output of the comparator circuit. The comparator circuit includes a differential pair arrangement that is imbalanced with a resistor. The differential pair in the comparator circuit is arranged to determine when the thermal voltage has reached a desired target level by evaluating two points within the thermal-voltage generator circuit. The comparator circuit can have a target level that is below 100% of full operation to improve reliability.
Claims20
An apparatus that is arranged to cooperate with a thermal-voltage generator circuit to assert a power-on reset (POR) signal during a start-up transient condition, wherein the thermal-voltage generator circuit includes a first bipolar junction device, a second bipolar junction device, and a resistor, the apparatus comprising:
- an imbalanced comparator circuit comprising a first MOS transistor, a second MOS transistor and a current source are arranged to cooperatively operate as a differential pair with an intentional input referred offset, wherein a gate of the first MOS transistor is coupled to a first internal point of the thermal-voltage generator circuit, a gate of the second MOS transistor is coupled to a second internal point of the thermal-voltage generator circuit, and a drain of the second MOS transistor is arranged as an output of the imbalanced comparator circuit;
- and
- an inverter circuit that is arranged to generate the POR signal responsive to the output of the imbalanced comparator circuit, wherein the cooperative operation of the imbalanced comparator circuit and the inverter circuit are arranged to evaluate the start-up transient condition such that the POR signal is asserted during the start-up transient condition until the thermal-voltage generator circuit is detected as reaching a target operating condition for stable operation.
An apparatus that is arranged to cooperate with a thermal-voltage generator circuit to assert a power-on reset (POR) signal during a start-up transient condition, the apparatus comprising:
- a thermal-voltage generator circuit comprising:
- an error amplifier that includes a first input coupled to a sixth node, a second input coupled to a fifth node, and an output coupled to a twelfth node;
- a first current source that is coupled to the sixth node, wherein the first current source is biased by the output of the error amplifier at the twelfth node;
- a second current source that is coupled to the fifth node, wherein the second current source is biased by the output of the error amplifier at the twelfth node;
- a resistor that is coupled between the fifth node and an eleventh node;
- a first bipolar junction device that is coupled to the sixth node;
- a second bipolar junction device that is coupled to the eleventh node;
- an imbalanced comparator circuit arranged in cooperation with the thermal-voltage generator circuit, the imbalanced comparator circuit comprising:
- a first MOS transistor that includes a drain coupled to a third node, a gate coupled to the fifth node, and a source coupled to a seventh node;
- a second MOS transistor that includes a drain coupled to a fourth node, a gate coupled to the sixth node, and a source coupled to the seventh node;
- a third MOS transistor that includes a drain and a gate coupled to the third node, and a source coupled to a first node;
- a fourth MOS transistor that includes a drain coupled to the fourth node, a gate coupled to the third node, and a source coupled to the first node;
- and
- a fifth MOS transistor that includes a drain coupled to the seventh node, a gate coupled to a tenth node, and a source coupled to a second node, wherein the imbalanced comparator circuit is arranged with an internal imbalance between the first MOS transistor and the second MOS transistor resulting in an input referred offset;
- and
- an inverter circuit that includes an input coupled to the fourth node, wherein the inverter circuit is arranged to cooperate with the imbalanced comparator circuit and such that the POR signal is asserted during the start-up transient condition until the thermal-voltage generator circuit is detected as reaching a target operating condition for stable operation.
An apparatus that is arranged to cooperate with a thermal-voltage generator circuit to assert a power-on reset (POR) signal during a start-up transient condition, the apparatus comprising:
- a thermal-voltage generator circuit comprising:
- an error amplifier that includes a first input coupled to a sixth node, a second input coupled to a fifth node, and an output coupled to a twelfth node;
- a first current source that is coupled to the sixth node, wherein the first current source is biased by the output of the error amplifier at the twelfth node;
- a second current source that is coupled to the fifth node, wherein the second current source is biased by the output of the error amplifier at the twelfth node;
- a resistor that is coupled between the fifth node and an eleventh node;
- a first bipolar junction device that is coupled to the sixth node;
- a second bipolar junction device that is coupled to the eleventh node;
- an imbalanced comparator circuit arranged in cooperation with the thermal-voltage generator circuit, the imbalanced comparator circuit comprising:
- a first MOS transistor that includes a drain coupled to a third node, a gate coupled to the fifth node, and a source coupled to a seventh node;
- a second MOS transistor that includes a drain coupled to a fourth node, a gate coupled to the eleventh node, and a source coupled to the seventh node;
- a third MOS transistor that includes a drain and a gate coupled to the third node, and a source coupled to a first node;
- a fourth MOS transistor that includes a drain coupled to the fourth node, a gate coupled to the third node, and a source coupled to the first node;
- and
- a fifth MOS transistor that includes a drain coupled to the seventh node, a gate coupled to a tenth node, and a source coupled to a second node, wherein the imbalanced comparator circuit is arranged with an internal imbalance between the first MOS transistor and the second MOS transistor resulting in an input referred offset;
- and
- an inverter circuit that includes an input coupled to the fourth node, wherein the inverter circuit is arranged to cooperate with the imbalanced comparator circuit and such that the POR signal is asserted during the start-up transient condition until the thermal-voltage generator circuit is detected as reaching a target operating condition for stable operation.
Dependencies are inferred from the claim text.