Detector of fast variation in the supply of integrated circuits
First Claim
1. An integrated circuit having a supply voltage terminal for a supply voltage Vcc, a ground terminal, and a detector of fast variations in said supply voltage Vcc at said supply voltage terminal, said detector comprising:
- a capacitor having first and second terminals, with said first terminal of said capacitor being connected to said ground terminal;
a first detection transistor having a gate, a source and a drain;
said source of said first detection transistor being connected to said supply voltage terminal, said drain of said first detection transistor being connected to an output terminal, and said gate of said first detection transistor being connected to said second terminal of said capacitor; and
a current limiting transistor having its gate connected to its drain, said current limiting transistor having a threshold voltage that is lower, in terms of absolute value, than the threshold voltage of said first detection transistor, said current limiting transistor being connected between said second terminal of said capacitor and said supply voltage terminal such that upon becoming conductive said current limiting transistor provides charging current to said capacitor to charge said capacitor to a voltage which is substantially Vcco-Vtn, where Vcco is a stable value of the supply voltage Vcc and Vtn is the threshold voltage of the current limiting transistor, thereby maintaining in a stable voltage supply mode a voltage drop between said supply voltage terminal and the gate of said first detection transistor which is the difference between the supply voltage and the voltage at the second terminal of said capacitor;
whereby, when the supply voltage Vcc varies swiftly from the stable voltage supply mode as compared with the charging time of said capacitor, the voltage drop between said supply voltage terminal and the gate of said first detection transistor increases and the conduction state of said first detection transistor changes when the thus increased voltage drop exceeds the threshold voltage of said first detection transistor;
whereby said detector can detect a fast variation in said supply voltage Vcc when the speed of the fast variation is faster than the charging rate of said capacitor.
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Accused Products
Abstract
Some integrated circuits need to be protected against malfunctioning due to the variations in the supply voltage Vcc. A detector of fast variations of the supply voltage is placed in the integrated circuit to interrupt or modify all or a part of the working of the general integrated circuit in the event of the occurrence of fast variation in Vcc. The detector includes a capacitor, a current limiter, a charging circuit, and a detection transistor. The current limiter is a transistor mounted as a diode. The charging circuit uses the supply voltage to charge the capacitor through the current limiter. The relatively stable voltage of the capacitor is applied to the gate of the detection transistor, which has a threshold voltage Vtp. The source of the detection transistor is connected to the voltage supply Vcc. If Vcc varies suddenly, the detector is made conductive. The assembly uses the difference between the threshold voltage Vtn of the current limiter and the threshold voltage Vtp of the detection transistor.
25 Citations
24 Claims
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1. An integrated circuit having a supply voltage terminal for a supply voltage Vcc, a ground terminal, and a detector of fast variations in said supply voltage Vcc at said supply voltage terminal, said detector comprising:
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a capacitor having first and second terminals, with said first terminal of said capacitor being connected to said ground terminal; a first detection transistor having a gate, a source and a drain;
said source of said first detection transistor being connected to said supply voltage terminal, said drain of said first detection transistor being connected to an output terminal, and said gate of said first detection transistor being connected to said second terminal of said capacitor; anda current limiting transistor having its gate connected to its drain, said current limiting transistor having a threshold voltage that is lower, in terms of absolute value, than the threshold voltage of said first detection transistor, said current limiting transistor being connected between said second terminal of said capacitor and said supply voltage terminal such that upon becoming conductive said current limiting transistor provides charging current to said capacitor to charge said capacitor to a voltage which is substantially Vcco-Vtn, where Vcco is a stable value of the supply voltage Vcc and Vtn is the threshold voltage of the current limiting transistor, thereby maintaining in a stable voltage supply mode a voltage drop between said supply voltage terminal and the gate of said first detection transistor which is the difference between the supply voltage and the voltage at the second terminal of said capacitor; whereby, when the supply voltage Vcc varies swiftly from the stable voltage supply mode as compared with the charging time of said capacitor, the voltage drop between said supply voltage terminal and the gate of said first detection transistor increases and the conduction state of said first detection transistor changes when the thus increased voltage drop exceeds the threshold voltage of said first detection transistor; whereby said detector can detect a fast variation in said supply voltage Vcc when the speed of the fast variation is faster than the charging rate of said capacitor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A process for detecting fast variations in the supply voltage at a supply voltage terminal of an integrated circuit even when the thus varied supply voltage does not exceed the range of nominal values of said supply voltage, said process comprising:
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applying said supply voltage to a current limiting transistor and a first detection transistor, wherein said current limiting transistor has a threshold voltage that is lower, in terms of absolute value, than the threshold voltage of said first detection transistor; providing a current flow through said current limiting transistor to a first terminal of a capacitor upon said supply voltage exceeding the threshold voltage of aid current limiting transistor to charge said capacitor to a voltage which is substantially Vcco-Vtn, where Vcco is the stable value of the supply voltage and Vtn is the threshold voltage of the current limiting transistor; applying the voltage at said first terminal of said capacitor to the gate of said first detection transistor; maintaining, in a stable voltage supply mode, the capacitor charged with a voltage at said first terminal of said capacitor which is substantially Vcco-Vtn, where Vcco is the stable value of the supply voltage and Vtn is the threshold voltage of the current limiting transistor, thereby maintaining at the gate of said first detection transistor a voltage which is the difference between the supply voltage and the voltage at the first terminal of said capacitor; whereby, when the supply voltage varies swiftly from the stable voltage supply mode as compared with the charging time of said capacitor, the voltage drop between said supply voltage terminal and the gate of said first detection transistor increases and the conduction state of said first detection transistor changes when the thus increased voltage drop exceeds the threshold voltage of said first detection transistor; and modifying the operation of a portion of the integrated circuit when said first detection transistor changes state after a stable voltage supply mode has been achieved. - View Dependent Claims (23, 24)
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Specification