Design Of New Built-In Temperature Sensor For DRAM

Refresh cycle time of The DRAM without TS is set to a fixed value.At low temperature,the DRAM data retention time is long.While at high temperature,the DRAM data retention time is short.To avoid data loss,the DRAM refresh cycle must be less than the DRAM data retention time at the high temperaure.Therefore,the DRAM refresh cycle is set to a smalle fixed value,resulting in a large DRAM standby power consumption in self-refresh mode.For the traditional built-in TS for DRAM,the incorrect judgment of the temperature is too high will lead to DRAM refresh cycle time is smaller,making the standby power consumption is too large.While the incorrect judgment of the temperature is too low will lead to DRAM refresh cycle is greater,making DRAM data retention time lead to failure.So the temperature sensing error of traditional built-in TS for DRAM will lead to no significant reduction in standby power consumption,in the more serious cases,there may be data retention failure and other reliability issues.In this paper,regarding DRAM built-in TS circuit structure characterization,the TS defects is analyzed,and the design requirements,system structure,sub-module structure and concrete realization method of new built-in TS for DRAM are given.Also in this paper,by improving the DRAM built-in TS FSM,adding test mode,enhanced testability and controllability.Based on the original resistor divider circuit,this design uses a separate bandgap reference circuit to produce a stable reference voltage.The design also uses the voltage divider resistor with same width and same shape,the interdigitional structure layout to eliminate process caused resistance deviation.The design uses resistance with small temperature coefficient,floorplan of resistance far away from high power consumption devices,even divided resistance fold end to end to eliminate temperature caused resistance deviation.Thereafter,resistance deviation due to the process,temperature was reduced,and high-precision voltage divider resistance was achieved.And at the same time,based on the original resistor divider circuit,two types of control resistance was added,temperature sensing drift error control resistance and temperature sensing slope error control resistor.Then,DRAM built-in TS resistor divider circuit performance and the temperature measurement accuracy are improved.According to the linear adjustment test results,the temperature range of the sample is linearly adjusted is from-32°C to 30°C,the adjustment precision is about 1°C.The Spec adjustment range is from-32°C to 31°C,the adjustment accuracy is 1°C.It is understood from the analysis that the linearity of the product meets the design requirements and is within the acceptable range from the verification result.Non-linear adjustment test results show that the product temperature slope adjustment range is from 9.76% to-12.2%,adjust the accuracy of about 2.44%.The Spec adjustment range is from 11% to-11% and the adjustment accuracy is 1.5%.Compared with verificaiton results,nonlinear adjustment meet the design requirements,and is consistent with the verification results.The important aspects of new built-in TS meet the requirements.