Semiconductor memory device
View Patent ↗A semiconductor memory device is provided for minutely changing a refresh interval according to a detected temperature and thereby lowering its power consumption. A temperature detector detects a temperature of a chip and outputs the corresponding temperature signal. A reference temperature signal output unit outputs the corresponding reference temperature signal with each of different reference temperatures to be compared with the chip temperature according to a selection signal. A temperature comparison unit compares the chip temperature with the reference temperature through the temperature signal and the reference temperature signal. A selection signal output unit outputs the selection signal according to the compared result of the temperature comparison unit. A refresh interval control unit changes the refresh interval according to the compared result of the temperature comparison unit.
1. A method of changing a refresh frequency in a semiconductor memory device, comprising:
detecting a temperature of the memory device to output a temperature signal;
comparing the temperature signal with a reference temperature signal to output a comparison result signal;
changing the refresh frequency according to the comparison result signal; and
selecting the reference temperature signal from a plurality of different reference temperature signals based on said comparison result signal.
2. The method according to claim 1 , wherein the refresh frequency is set to higher when the temperature is higher than a reference temperature.
3. The method according to claim 1 , further comprising:
selecting a frequency dividing number of a divider according to the comparison result signal to generate the refresh frequency.
4. The method according to claim 1 , further comprising:
selecting a start reference temperature signal, when a power is turned on, so that a refresh frequency becomes high; and
comparing the temperature signal with the start reference temperature signal.
5. The method according to claim 1 , wherein the plurality of different reference temperature signals are generated based on a voltage that does not depend on variations of the temperature and a power supply.
6. The method according to claim 1 , wherein each of the plurality of different reference temperature signals corresponds to one of a plurality of temperatures which are set by incrementing a start temperature by a certain value until reaching an end temperature.
7. The method according to claim 1 , further comprising:
latching the comparison result signal into a latch circuit.
8. A method of changing an interval period between a refresh operation in a semiconductor memory device, comprising:
detecting temperature of said memory device for outputting a temperature signal;
comparing the temperature signal with a reference temperature signal to output a comparison result;
changing the interval period between the refresh operation according to said comparison result; and
selecting the reference temperature signal based on said comparison result.
9. The method according to claim 8 , wherein the interval period set to shorter when the temperature is higher than a reference temperature.
10. The method according to claim 8 , further comprising:
selecting a frequency dividing number of a divider according to the comparison result to generate the refresh frequency.
11. The method according to claim 8 , further comprising:
selecting a start reference temperature signal, when a power is turned on, so that the interval period becomes short;
comparing the temperature signal with the start reference temperature signal.
12. The method according to claim 8 , wherein the plurality of different reference temperature signals are generated based on a voltage that does not depend on variations of the temperature and a power supply.
13. The method according to claim 8 , wherein each of the plurality of different reference temperature signals corresponds to one of a plurality of temperatures which are set by incrementing a start temperature by a certain value until reaching an end temperature.
14. The method according to claim 8 , further comprising:
latching the comparison result signal into a latch circuit.