Temperature sensing circuit and semiconductor memory device using the same

1. A temperature sensing circuit comprising

a temperature sensing unit for generating a reference voltage having a constant level, regardless or a temperature fluctuation, and a variable voltage to be changed according to the temperature fluctuation; and

a comparison unit for comparing the reference voltage to the variable voltage, detecting an ambient temperature and generating a temperature detecting signal,

wherein the temperature sensing unit comprises

a plurality of voltage dividing elements connected in series between a driving voltage supply terminal for receiving the driving voltage and a first node,

an enable element connected between the first node and a ground voltage level in order to enable an operation of the voltage dividing elements in response to a first enable signal,

a control voltage generating unit for generating a first voltage in response to the reference voltage, the control voltage generating unit including a first level controlling element connected between the driving voltage supply terminal and a second node, and

a first temperature element connected between the first node and the second node to generate the first voltage in response to the reference voltage, and

an amplifying unit for generating the variable voltage in response to the first voltage.

2. The temperature sensing circuit of claim 1 , wherein the amplifying unit includes:

a second level controlling element connected between the driving voltage supply terminal and a third node; and

a second temperature element connected between the first node and the third node to generate the variable voltage in response to the first voltage.

3. The temperature sensing circuit of claim 1 , wherein the amplifying unit includes:

a second level controlling element connected between the driving voltage supply terminal and a third node;

a second temperature element connected between the first node and the third node and generating a second voltage in response to the first voltage;

a third level controlling element connected between the driving voltage supply terminal and a fourth node; and

a second temperature element connected between the first node and the fourth node to generate the variable voltage in response to the second voltage.

4. The temperature sensing circuit of claim 1 , wherein the comparison unit includes a differential amplifier.

5. The temperature sensing circuit of claim 1 , further comprising a temperature sensing control unit configured to receive a first enable signal and a period signal and generate a second enable signal for enabling the temperature sensing unit and the comparison unit every period of the period signal.

6. The temperature sensing circuit of claim 5 , wherein the temperature sensing control unit generates a counter pulse for sampling the temperature detecting signal.

7. The temperature sensing circuit of claim 6 , further comprising a flag signal generating unit for sampling the temperature detecting signal in response to the counter pulse and generating a flag signal having temperature information, wherein the flag signal is enabled when the sampled temperature detecting signal is enabled at least once.

8. The temperature sensing circuit of claim 1 , further comprising a temperature sensing control unit which includes:

a first logic element for performing a first logic operation to a first enable signal and a period signal;

a delay unit for generating a second enable signal, which is enabled every period of the period signal, by delaying an output signal of the first logic element; and

a logic unit for generating a counter pulse for sampling the temperature detecting signal by performing a second logic operation to an output signal of the first logic element and another signal which is produced by delaying the output signal of the first logic element.

9. The temperature sensing circuit of claim 8 , further comprising:

a flag signal generating unit including a counting unit configured to receive the temperature detecting signal and generate a plurality of counting signals in response to the counter pulse; and

a signal processing unit configured to receive the plurality of counting signals and then generate a flag signal having temperature information therein, wherein the flag signal is enabled when all of the plurality of counting signals are enabled.

10. The temperature sensing circuit of claim 9 , wherein the counting unit is initialized in response to the first enable signal.