Periodic signal generating circuit dependent upon temperature for establishing a temperature independent refresh frequency

Abstract

A periodic signal generating circuit which is dependent upon temperature for establishing a temperature independent refresh frequency is presented. The periodic signal generating circuit includes a reference voltage generating unit and a periodic signal generating unit. The reference voltage generating unit produces a reference voltage which exhibits a variable voltage level in response to temperature. The periodic signal generating unit produces a periodic signal in response to a set voltage to determine the reference voltage and an oscillation period, wherein a transition timing of the set voltage is controlled by the reference voltage. As a result the periodic signal has a relatively constant period which can be produced regardless of the temperature variation.

What is claimed is: 
     
         1 . A periodic signal generating circuit comprising:
 a reference voltage generating unit configured to include a current mirror having a resistor and output a reference voltage that exhibits a variable voltage level which becomes higher when the temperature is lowered by using a temperature variation characteristic of the resistor; and   a periodic signal generating unit configured to produce a periodic signal in response to a difference between a node voltage and the reference voltage.   
     
     
         2 . The periodic signal generating circuit of  claim 1 , wherein the periodic signal generating unit includes:
 a differential amplifying unit configured to produce an oscillation control signal by detecting the voltage difference between the node voltage and the reference voltage;   an oscillation unit configured to produce the periodic signal in response to the oscillation control signal; and   a charging/discharging unit configured to charge or discharge the node voltage in response to the periodic signal and the reference voltage.   
     
     
         3 . The periodic signal generating circuit of  claim 2 , wherein the charging/discharging unit is configured to charge or discharge the node voltage in response to the periodic signal and control a transition time of the node voltage in response to the reference voltage. 
     
     
         4 . The periodic signal generating circuit of  claim 3 , wherein the charging/discharging unit is configured to control a resistance value along a discharging current path as a function of temperature. 
     
     
         5 . The periodic signal generating circuit of  claim 4 , wherein the charging/discharging unit includes capacitors in parallel to each other and is coupled to a plurality of resistors. 
     
     
         6 . The periodic signal generating circuit of  claim 5 , wherein the charging/discharging unit is configured to control a RC response by controlling the resistance value along the discharging current path in response to the reference voltage. 
     
     
         7 . A periodic signal generating circuit comprising:
 a reference voltage generating unit configured to include a current mirror having a resistor and output a reference voltage that exhibits a variable voltage level which becomes higher when the temperature is lowered by using a temperature variation characteristic of the resistor; and   a periodic signal generating unit configured to produce a periodic signal in response to a difference between a node voltage and the reference voltage, wherein the node voltage and the reference voltage are in complementary relations with temperature variation.   
     
     
         8 . The periodic signal generating circuit of  claim 7 , wherein the periodic signal generating unit includes:
 a differential amplifying unit configured to produce an oscillation control signal by detecting the voltage difference between the node voltage and the reference voltage;   an oscillation unit configured to produce the periodic signal in response to the oscillation control signal; and   a charging/discharging unit configured to charge or discharge the node voltage in response to the periodic signal and the reference voltage.   
     
     
         9 . The periodic signal generating circuit of  claim 8 , wherein charging/discharging unit configured to control a discharge time of the node voltage in response to the reference voltage. 
     
     
         10 . The periodic signal generating circuit of  claim 9 , wherein the charging/discharging unit is configured to control a resistance value along a discharging current path as a function of temperature. 
     
     
         11 . The periodic signal generating circuit of  claim 10 , wherein the charging/discharging unit includes capacitors in parallel to each other and is coupled to a plurality of resistors. 
     
     
         12 . The periodic signal generating circuit of  claim 11 , wherein the charging/discharging unit is configured to control a RC response by controlling the resistance value along the discharging current path in response to the reference voltage.