POWER SUPPLY VOLTAGE TRANSITION COMPARISON CIRCUIT, POWER SUPPLY VOLTAGE TRANSITION COMPARISON METHOD, AND SEMICONDUCTOR INTEGRATED CIRCUIT

• US 20150022240A1
• Filed: 06/12/2014
• Published: 01/22/2015
• Est. Priority Date: 07/17/2013
• Status: Active Grant

• Current Assignee: Renesas Electronics Corporation
• Original Assignee: Renesas Electronics Corporation
• Inventors: Soraoka, Makoto
• Granted Patent: US 9,214,930 B2
• Time in Patent Office: Days
• US Class Current: 327/76
• CPC Class Codes: G01R 19/16552 in I.C. power supplies
• CPC Class Codes: G06F 1/28 Supervision thereof, e.g. detecting power-supply failure by out of limits supervision
• CPC Class Codes: G06F 1/3212 Monitoring battery levels, e.g. power saving mode being initiated when battery voltage goes below a certain level
• CPC Class Codes: H03K 5/1534 Transition or edge detectors

Abstract

The power supply voltage transition comparison circuit includes a comparator evaluation voltage setting circuit, a comparator, a voltage evaluation circuit, and an evaluation voltage setting value output circuit. The comparator evaluation voltage setting circuit generates a divided voltage of one of a power supply voltage and a reference voltage. The comparator compares the other of the power supply voltage and the reference voltage with the divided voltage. The voltage evaluation circuit evaluates the power supply voltage based on a result of a comparison between the other voltage and the divided voltage. The evaluation voltage setting value output circuit changes a ratio between the one voltage and the divided voltage based on a result of an evaluation of the power supply voltage.

Claims

1. A power supply voltage transition comparison circuit comprising:

a comparator evaluation voltage setting circuit that generates a divided voltage of one of a power supply voltage and a reference voltage;

a comparator that compares the other of the power supply voltage and the reference voltage with the divided voltage;

a voltage evaluation circuit that evaluates the power supply voltage based on a result of a comparison between the other voltage and the divided voltage; and

an evaluation voltage setting value output circuit that changes a ratio between the one voltage and the divided voltage based on a result of an evaluation of the power supply voltage.

2. The power supply voltage transition comparison circuit according to claim 1, further comprising:

a voltage evaluation control circuit that determines whether or not a power supply voltage transition matches an expected voltage transition based on the result of the evaluation of the power supply voltage; and

a setting circuit that holds a setting value of the expected voltage transition, the setting circuit being able to change the setting value.

3. The power supply voltage transition comparison circuit according to claim 1, further comprising:

a setting circuit that holds a setting value, the setting circuit being able to change the setting value; and

a voltage evaluation control circuit that determines a timing at which the voltage evaluation circuit evaluates the power supply voltage based on the setting value.

4. The power supply voltage transition comparison circuit according to claim 1, further comprising:

a setting circuit that holds a setting value, the setting circuit being able to change the setting value; and

a voltage evaluation control circuit that determines the number of times that the evaluation voltage setting value output circuit changes the ratio between the one voltage and the divided voltage based on the setting value.

5. The power supply voltage transition comparison circuit according to claim 1, further comprising a setting circuit that holds a setting value, the setting circuit being able to change the setting value, wherein

the evaluation voltage setting value output circuit sets the ratio between the one voltage and the divided voltage based on the setting value.

6. The power supply voltage transition comparison circuit according to claim 1, wherein

the divided voltage includes a first divided voltage and a second divided voltage,

the evaluation voltage setting value output circuit sets a ratio between the one voltage and the first divided voltage based on an upper-limit voltage of an expected voltage range and sets a ratio between the one voltage and the second divided voltage based on a lower-limit voltage of the expected voltage range,

the comparator evaluation voltage setting circuit comprises:

a first voltage-dividing circuit that generates the first divided voltage from the one voltage; and

a second voltage-dividing circuit that generates the second divided voltage from the one voltage,

the comparator comprises;

a first comparator that compares the other voltage with the first divided voltage; and

a second comparator that compares the other voltage with the second divided voltage, and

the voltage evaluation circuit determines whether or not the power supply voltage is within the expected voltage range based on an output of the first comparator and an output of the second comparator.

7. The power supply voltage transition comparison circuit according to claim 1, wherein

the evaluation voltage setting value output circuit changes a voltage setting mode between an upper-limit voltage setting mode in which the ratio between the one voltage and the divided voltage is set based on an upper-limit voltage of an expected voltage range, and a lower-limit voltage setting mode in which the ratio between the one voltage and the divided voltage is set based on a lower-limit voltage of the expected voltage range based on an upper/lower selector signal output by the voltage evaluation circuit, and

the voltage evaluation circuit determines whether or not the power supply voltage is within the expected voltage range based on an output of the comparator.

8. The power supply voltage transition comparison circuit according to claim 7, wherein the voltage evaluation circuit secures a predetermined wait time after the voltage evaluation circuit changes the upper/lower selector signal from a value indicating one of the upper-limit voltage setting mode and the lower-limit voltage setting mode to a value indicating the other of the upper-limit voltage setting mode and the lower-limit voltage setting mode, and then determines whether the power supply voltage is lower than the upper-limit voltage or determines whether the power supply voltage is higher than the lower-limit voltage based on the output of the comparator.

9. The power supply voltage transition comparison circuit according to claim 1, further comprising a voltage evaluation control circuit, wherein

the voltage evaluation control circuit comprises an evaluation step counter that counts the number of evaluation steps based on the result of the evaluation of the power supply voltage output from the voltage evaluation circuit, and outputs a count value of the evaluation step counter to the evaluation voltage setting value output circuit,

the evaluation voltage setting value output circuit sets a ratio between the one voltage and the divided voltage based on a setting value associated with the count value, and

the voltage evaluation control circuit outputs a lock cancellation signal indicating a cancellation of a lock of an access-protected circuit when the count value of the evaluation step counter is an upper-limit value for the evaluation step number and the evaluation result of the power supply voltage output from the voltage evaluation circuit indicates that the power supply voltage is within an expected voltage range.

10. The power supply voltage transition comparison circuit according to claim 9, wherein the voltage evaluation control circuit secures a predetermined wait time after the voltage evaluation control circuit outputs the count value, and then instructs the voltage evaluation circuit to evaluate the power supply voltage.

11. The power supply voltage transition comparison circuit according to claim 1, further comprising a reference voltage generation circuit that generates the reference voltage from the power supply voltage, wherein

the one voltage is the power supply voltage, and

the other voltage is the reference voltage.

12. A semiconductor integrated circuit comprising:

an access-protected circuit;

a power supply voltage transition comparison circuit that determines whether or not a power supply voltage transition matches an expected voltage transition, and outputs a lock cancellation signal when the power supply voltage transition matches the expected voltage transition; and

a lock control circuit that cancels a lock of the access-protected circuit based on the lock cancellation signal, wherein

the power supply voltage transition comparison circuit comprises;

a comparator evaluation voltage setting circuit that generates a divided voltage of one of a power supply voltage and a reference voltage;

a comparator that compares the other of the power supply voltage and the reference voltage with the divided voltage;

a voltage evaluation circuit that evaluates the power supply voltage based on a result of a comparison between the other voltage and the divided voltage; and

an evaluation voltage setting value output circuit that changes a ratio between the one voltage and the divided voltage based on a result of an evaluation of the power supply voltage.

13. A power supply voltage transition comparison method comprising:

generating a divided voltage of one of a power supply voltage and a reference voltage;

comparing the other of the power supply voltage and the reference voltage with the divided voltage;

evaluating the power supply voltage based on a result of a comparison between the other voltage and the divided voltage; and

changing a ratio between the one voltage and the divided voltage based on a result of an evaluation of the power supply voltage.

14. The power supply voltage transition comparison method according to claim 13, further comprising:

holding a setting value for an expected voltage transition, the setting value being changeable, and

determining whether or not a transition of the power supply voltage matches the expected voltage transition based on the result of the evaluation of the power supply voltage.

15. The power supply voltage transition comparison method according to claim 13, further comprising:

setting a ratio between the one voltage and a first divided voltage based on an upper-limit voltage of an expected voltage range, and

setting a ratio between the one voltage and a second divided voltage based on a lower-limit voltage of the expected voltage range, wherein

the generating of the divided voltage comprises;

generating, by a first voltage-dividing circuit, the first divided voltage from the one voltage; and

generating, by a second voltage-dividing circuit, the second divided voltage from the one voltage,

the comparing of the other voltage with the divided voltage comprises;

comparing, by a first comparator, the other voltage with the first divided voltage; and

comparing, by a second comparator, the other voltage with the second divided voltage, and

the evaluating of the power supply voltage comprises determining whether or not the power supply voltage is within the expected voltage range based on an output of the first comparator and an output of the second comparator.

16. The power supply voltage transition comparison method according to claim 13, further comprising changing, by a voltage evaluation circuit, a voltage setting mode between an upper-limit voltage setting mode and a lower-limit voltage setting mode, wherein

in the upper-limit voltage setting mode, a ratio between the one voltage and the divided voltage is set based on an upper-limit voltage of an expected voltage range,

in the lower-limit voltage setting mode, the ratio between the one voltage and the divided voltage is set based on a lower-limit voltage of the expected voltage range, and

the evaluating of the power supply voltage comprises evaluating, by the voltage evaluation circuit, whether or not the power supply voltage is within the expected voltage range based on an output of a comparator that compares the other voltage with the divided voltage.

17. The power supply voltage transition comparison method according to claim 13, further comprising:

counting the number of evaluation steps based on the result of the evaluation of the power supply voltage;

outputting a count value of the evaluation step number;

setting, in the setting of the ratio between the one voltage and the divided voltage, the ratio between the one voltage and the divided voltage based on a setting value associated with the count value, and

cancelling a lock of an access-protected circuit when the count value of the evaluation step number is an upper-limit value for the evaluation step number and the evaluation result of the power supply voltage indicates that the power supply voltage is within an expected voltage range.

18. The power supply voltage transition comparison method according to claim 13, further comprising generating the reference voltage from the power supply voltage, wherein

the one voltage is the power supply voltage, and

the other voltage is the reference voltage.

19. The power supply voltage transition comparison method according to claim 13, further comprising:

determining whether or not a power supply voltage transition matches an expected voltage transition based on the result of the evaluation of the power supply voltage; and

cancelling a lock of an access-protected circuit when the power supply voltage transition matches the expected voltage transition.