Apparatuses and methods for DRAM wordline control with reverse temperature coefficient delay
Apparatuses and methods for a temperature dependent delay between a wordline off signal and deactivating the wordline are disclosed. Memory devices may have reduced reliability when operating at relatively cold temperatures, which may be due in part to an increase in the write recovery time while the timing for a wordline to deactivate remains relatively unaffected. In some embodiments of the present disclosure, a delay circuit is used to insert a temperature dependent delay between a wordline off command being issued and the wordline being deactivated. The delay circuit may increase the length of temperature dependent delay at relatively cold temperatures, and decrease the length of the delay at relatively warm temperatures.
1. An apparatus comprising:
a memory cell array; and
a delay circuit coupled to the memory array, wherein the delay circuit receives a command signal and provides it to the memory array after a delay time, wherein the delay time has a length which is responsive to a temperature, and wherein the delay circuit is configured to increase the delay time in response to a first temperature and decrease the delay in response to a second temperature that is greater than the first temperature, and wherein the command signal is a pre-charge signal.
2. The apparatus of claim 1 , further comprising a temperature sensor coupled to the memory array and configured to output a signal proportional to a temperature of the memory array.
3. The apparatus of claim 2 , wherein the delay circuit is a programmable delay circuit coupled to the temperature sensor and responsive to the signal from the temperature sensor.
4. The apparatus of claim 1 , wherein the delay circuit comprises an analogue circuit responsive to a temperature of the delay circuit.
5. The apparatus of claim 4 , wherein the analogue circuit comprises a plurality of inverters and at least one RC delay circuit coupled between the plurality of inverters.
6. The apparatus of claim 5 , wherein one of the plurality of inverters comprises provides a fast pull-up signal transition, and another of the plurality of inverters provides a fast pull down signal transition.
7. The apparatus of claim 1 , wherein the memory cell array comprises a plurality of wordlines, each of the wordlines coupled to a respective wordline driver circuit, wherein at least one of the respective wordline driver circuits is configured to receive the command signal.
8. The apparatus of claim 7 , wherein the wordline driver circuit is configured to reduce the voltage of the wordline in response to receipt of a first signal, and further configured to couple the wordline to a ground voltage in response to receipt of the command signal after the delay time, wherein the first signal is received before the command signal.
9. A method comprising:
receiving a command signal at a memory device at a first time;
deactivating a wordline of the memory device in response to the command signal at a second time, wherein a time between the first time and the second time is based, at least in part, on a propagation delay and a configurable delay generated by a delay circuit; and
adjusting the configurable delay based on a temperature of the memory device, wherein a length of the configurable delay is responsive to the temperature, and wherein the adjusting comprises:
increasing the configurable delay in response to a decrease in the temperature; and
decreasing the configurable delay in response to an increase in the temperature.
10. The method of claim 9 , wherein the proportion of the configurable delay to the propagation delay is increased in response to the decrease in the temperature, and wherein the proportion of the configurable delay to the propagation delay is decreased in response to the increase in the temperature.
11. The method of claim 9 , further comprising decreasing the time between the first time and the second time in response to the decrease in temperature.
12. The method of claim 9 , further comprising:
measuring the temperature of the memory device based on an input from a temperature sensor; and
providing the measured temperature to the delay circuit, wherein the delay circuit generates the configurable delay in response to the measured temperature.
13. The method of claim 9 further comprising reducing stress on a wordline driver circuit based on the delay between the first time and the second time.