US 5,497,112 A · Power-out reset system

Abstract

A power-out reset circuit includes reference voltage and current generators to generate a reference voltage and a reference current which are essentially independent of temperature variations over a useful temperature range, a delay/disable circuit, over and under voltage detectors and output logic circuitry. This circuit detects when the voltage level of a supply voltage source (+VDD) exceeds preselected limits. The reference voltage, which is related to the silicon band gap voltage, is connected to a first input of a comparator of each of the voltage detectors. The reference current, which is derived from the silicon band gap voltage, is connected to a current source of each of the detectors. Each detector has a hysteresis circuit which changes the point at which the comparator switches in the event that +VDD crosses into or outside of a preselected operating range. The delay/disable circuit ensures that the reference voltage is stable before the voltage detectors are activated, and that the voltage detectors are disabled when the supply voltage source falls below a minimum value which causes the reference voltage to be invalid (i.e., to be outside the preselected operating range. Outputs of the comparators are coupled to the output logic circuitry. The output logic circuitry includes a two input EXCLUSIVE OR logic circuit, a delay circuit, a two input OR logic gate, a transistor, a two input NOR logic gate, and an inverter.

Claims29

Dependent claims

Circuitry for detecting if a voltage level of a voltage source exceeds preselected voltage levels comprising:

reference voltage generator means for generating first and second reference voltages at first and second outputs, respectively, thereof;
delay/disable means, which has an input coupled to the second output of the reference voltage generator means, and which has an output, for generating, after a predetermined delay, a third reference voltage at the output of the delay/disable means, and for generating a disable output signal at the output of the delay/disable means if the voltage level of the voltage source is below a minimum level;
voltage detector means, which has a first input which is coupled to the first output of the reference voltage generator means, which has a second input coupled to the output of the delay/disable means, and which has a third input coupled through a voltage translator network thereof to a voltage source terminal, the voltage source terminal being connectable to the voltage source, for detecting if the voltage level of the voltage source is within the preselected voltage levels and for generating at outputs thereof signals indicative of whether the voltage level of the voltage source is within or outside the preselected voltage levels, and for being disabled if the voltage level of the voltage source is below the minimum level.

Circuitry for detecting if a voltage level of a supply voltage source exceeds preselected voltage levels comprising:

reference voltage generator means for generating first and second reference voltages at first and second outputs, respectively, with the first voltage being characterized by being independent of temperature variations over a useful temperature range;
delay/disable means, which comprises a first current generator coupled to an input thereof, which has an output, and which has the input thereof coupled to the second output of the reference voltage generator means, for generating at the output thereof a third reference voltage;
the second reference voltage being characterized in that with same coupled to the first current generator there results in generation in the first current generator of a current having a level which is essentially independent of temperature variations over a useful temperature range;
voltage detector means, which comprises a second current generator coupled to a first input thereof which is coupled to the output of the delay/disable means, which has a second input thereof coupled to the first output of the reference voltage generator means, and which has a third input coupled through a first voltage translator network thereof to a supply voltage source terminal, the supply voltage source terminal being connectable to the supply voltage source;
the third reference voltage being characterized in that with same coupled to the second current generator there results in generation of a current in the second current generator which is essentially independent of temperature variations over a useful temperature range;
and
the voltage detector means being for detecting if the voltage level of the voltage source is within the preselected voltage levels and for generating at outputs thereof signals indicative of whether the voltage level of the voltage source is within or outside the preselected voltage levels, and for being disabled if the voltage level of the voltage source is below the minimum level.

4 more elements

Circuitry for detecting if a voltage level of a voltage source exceeds preselected voltage levels comprising:

reference voltage generator means for generating first and second reference voltages at first and second outputs, respectively, thereof;
delay/disable means, which has an input coupled to the second output of the reference voltage generator means, and which has an output, for generating, after a predetermined delay, a third reference voltage at the output of the delay/disable means, and for generating a disable output signal at the output of the delay/disable means if the voltage level of the voltage source is below a minimum level;
voltage detector means, which has a first input which is coupled to the first output of the reference voltage generator means, which has a second input coupled to the output of the delay/disable means, and which has a third input coupled through a voltage translator network thereof to a voltage source terminal, the voltage source terminal being connectable to the voltage source, for detecting if the voltage level of the voltage source is within the preselected voltage levels and for generating at an output thereof a signal indicative of whether the voltage level of the voltage source is within or outside the preselected voltage levels, and for being disabled if the voltage level of the voltage source is below the minimum level;
the voltage detector means comprising hysteresis means which is coupled to the voltage translator network, and which has an input coupled to an output of the voltage detector means, for selectively modifying a voltage generated at the third input of the voltage detector means such that an output signal of the voltage detector means has an increased tendency not to switch states due to relatively short duration changes in the voltage level of the voltage source due to noise;
and
output logic circuitry means, which has inputs coupled to outputs of the voltage detector means, and which has an output which serves as the circuitry output, for processing signals received from the voltage detector means and generating an output signal that that initiates if the voltage level of the voltage source is within the preselected voltage levels or outside of same, and if the voltage level of the voltage source had exceeded the preselected voltage levels and then returned to a voltage level within the preselected voltage levels, for delaying any change in a signal generated at the output circuitry terminal such that a resulting output signal at the circuitry output terminal has an increased tendency not to switch states due to relatively short duration changes in the voltage level of the voltage source due to noise after the output logic circuitry means has provided an output signal at the output thereof indicating the voltage level of the voltage source is outside the preselected voltage levels.

3 more elements

Circuitry for detecting if a voltage level of a supply voltage source exceeds preselected voltage levels comprising:

reference voltage generator means for generating first and second reference voltages at first and second outputs, respectively, with the first voltage being characterized by being independent of temperature variations over a useful temperature range;
delay/disable means, which comprises a first current generator coupled to an input thereof, which has an output and has the input thereof coupled to the second output of the reference voltage generator means, for generating at an output thereof a third reference voltage;
the second reference voltage being characterized when same is coupled to the first current generator there results in generation of a current having a level which is essentially independent of temperature variations over a useful temperature range being generated by the first current generator;
voltage detector means, which comprises a second current generator coupled to an input thereof which is coupled to the output of the delay/disable means, which has a second input thereof coupled to the first output of the reference voltage generator means, and which has a third input coupled through a first voltage translator network thereof to a supply voltage source terminal, the supply voltage source terminal being connectable to the supply voltage source;
the third reference voltage being characterized in that when same is coupled to the second current generator there results in the generation of a current level in the second current generator which is essentially independent of temperature variations over a useful temperature range;
the voltage detector means being for detecting if the voltage level of the supply voltage source is within the preselected voltage levels and for generating at outputs thereof signals indicative of whether the voltage level of the supply voltage source is within or outside the preselected levels, and for being disabled if the voltage level of the supply voltage source is below the minimum level;
the voltage detector means further comprising hysteresis means which is coupled to the voltage translator network and has an input coupled to an output of the voltage detector means, for selectively modifying a voltage generated at the third input of the voltage detector means such that an output signal of the voltage detector means has an increased tendency not to switch states due to relatively short duration changes in the voltage level of the supply voltage source due to noise;
and
output logic circuitry means, which has inputs coupled to outputs of the voltage detector means and has an output which serves as the circuitry output, for processing signals received from the voltage detector means and generating an output signal that that indicates if the voltage level of the supply voltage source is within the preselected voltage levels or outside of same, and if previously thereto the voltage level of the supply voltage source had exceeded the preselected voltage levels, for delaying any change in a signal generated at the output circuitry terminal such that a resulting output signal at the circuitry output terminal has an increased tendency not to switch states due to relatively short duration changes in the voltage level of the supply voltage source due to noise after same has provided a signal indicating the voltage level of the supply voltage source is outside the preselected limits.

6 more elements

Dependencies are inferred from the claim text.

Power-out reset system

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Power-out reset system

Life of this patent

Abstract

Claims29