Devices and methods for controlling active termination resistors in a memory system

Abstract

A termination resistor is mounted on a memory circuit and provides a termination resistance for the memory circuit. The termination resistor includes a node, a plurality of first termination resistors responsive to a corresponding control signal and connected between a power voltage and the node, and a plurality of second termination resistors responsive to a corresponding control signal and connected between a ground voltage and the node.

What is claimed is: 
     
       1. A memory circuit, comprising:
 a node; and 
 a termination resistor which provides a termination resistance for the memory circuit, comprises a plurality of resistors which are selectively connected between the node and a reference voltage; and 
 a control circuit which receives an externally supplied active termination control signal, to synchronously switch on and off a connection of the node to the reference voltage through the termination resistor according to the active termination control signal in a first mode of operation of the memory circuit, and to asynchronously switch the connection of the node to the reference voltage through the termination resistor according to the active termination control signal in a second mode of operation of the memory circuit. 
 
     
     
       2. The memory circuit as claimed in  claim 1 , wherein the connection is switched on and off in synchronization with an external clock signal and in accordance with the active termination control signal in the first mode. 
     
     
       3. The memory circuit as claimed in  claim 2 , wherein the connection is switched on and off asynchronously with respect to the external clock signal in accordance with the active termination control signal in the second mode. 
     
     
       4. The memory circuit of  claim 3 , wherein the memory circuit is formed within a semiconductor chip. 
     
     
       5. The memory circuit as claimed in  claim 3 , wherein the first mode is an active operation mode of the memory circuit. 
     
     
       6. The memory circuit as claimed in  claim 5 , wherein the second mode is a power down mode of the memory circuit. 
     
     
       7. The memory circuit as claimed in  claim 6 , further comprising a synchronization circuit for generating an internal clock signal, which is activated in the first mode and deactivated in the second mode. 
     
     
       8. The memory circuit as claimed in  claim 7 , wherein the synchronization circuit is one of a delay locked loop circuit and a phase locked loop circuit. 
     
     
       9. The memory circuit as claimed in  claim 8 , wherein the connection of the node to the reference voltage through the termination resistor is off when data is read from the memory circuit. 
     
     
       10. The memory circuit as claimed in  claim 9 , wherein, in the second mode, the connection of the node to the reference voltage through the termination resistor is switched on after a predetermined length of time after the active termination control signal is received. 
     
     
       11. The memory circuit as claimed in  claim 10 , the predetermined length of time is does not vary in response to the external clock signal. 
     
     
       12. The memory circuit as claimed in  claim 11 , further comprising a mode register to store data used in determining the operation mode. 
     
     
       13. A memory comprising:
 a node connected to a terminal of the memory; and 
 a termination resistor which provides a termination resistance for the memory circuit selectively connected between the node and a reference voltage; and 
 a control circuit which synchronously switches on and off the selective connection of the termination resistor between the node and the reference voltage according to an externally supplied active termination control signal when the memory circuit is in an active operational mode, and which asynchronously modifies the selective connection of the termination resistor between the node and the reference voltage according to the active termination control signal when the memory circuit is in an asynchronous mode comprising at least one of a standby mode and a power down operational mode. 
 
     
     
       14. The memory as claimed in  claim 13 , further comprising a synchronization circuit for generating an internal clock signal, which is activated in the active operational mode and deactivated in the asynchronous mode. 
     
     
       15. The memory as claimed in  claim 14 , wherein the synchronization circuit is one of a delay locked loop circuit and a phase locked loop circuit. 
     
     
       16. The memory as claimed in  claim 15 , wherein the selective connection of the termination resistor is disconnected when data is read from the memory circuit. 
     
     
       17. The memory as claimed in  claim 16 , wherein in the asynchronous mode, the selective connection of the termination resistor is connected after a predetermined length of time after receipt of the active termination control signal. 
     
     
       18. The memory as claimed in  claim 17 , the predetermined length of time is not proportional to a period of any received external clock signal. 
     
     
       19. The memory as claimed in  claim 13 , wherein the termination resistor comprises:
 a first UP resistor which is selectively connected between the first reference voltage and the node in response to a first control signal; and 
 a second UP resistor which is selectively connected between the first reference voltage and the node in response to a second control signal. 
 
     
     
       20. The memory as claimed in  claim 19 , wherein the termination resistor further comprises:
 a first DOWN resistor which is selectively connected between the second reference voltage and the node in response to a third control signal; and 
 a second DOWN resistor which is selectively connected between the second reference voltage and the node in response to a fourth control signal. 
 
     
     
       21. A memory, comprising:
 a semiconductor memory chip including a terminal, an input buffer connected to the terminal and a termination circuit connected the terminal, the termination circuit comprising: 
 a node connected to the terminal of the memory chip; and 
 a termination resistor which provides a termination resistance for the memory chip, comprises a plurality of resistors which are selectively connected between the node and a reference voltage; and 
 a control circuit which receives an externally supplied active termination control signal, to synchronously switch on and off a connection of the node to the reference voltage through the termination resistor according to the active termination control signal in a first mode of operation of the memory chip, and to asynchronously switch the connection of the node to the reference voltage through the termination resistor according to the active termination control signal in a second mode of operation of the memory chip. 
 
     
     
       22. The memory as claimed in  claim 21 , wherein the connection is switched on and off in synchronization with an external clock signal and in accordance with the active termination control signal in the first mode. 
     
     
       23. The memory as claimed in  claim 22 , wherein the connection is switched on and off asynchronously with the external clock signal in accordance with the active termination control signal in the second mode. 
     
     
       24. A method of operating a memory, comprising:
 in a first mode of operation of the memory: 
 receiving an active termination control signal; 
 in response to the receipt of the active termination control signal, switching on and off a connection of a resistance between a node and a reference voltage in synchronism with an external clock received by the memory, the node being connected to a terminal of the memory; and 
 in a second mode of operation of the memory: 
 receiving an active termination control signal; 
 in response to the receipt of the active termination control signal, switching on and off the connection of the resistance between the node and the reference voltage independent of a switching timing of the external clock received by the memory. 
 
     
     
       25. The method of  claim 24 , wherein the second mode of operation comprises a power down mode of operating the memory. 
     
     
       26. The method of  claim 24 , wherein the second mode of operation comprises a standby mode of operating the memory. 
     
     
       27. The method of  claim 24 , further comprising:
 generating an internal clock during the first mode of operation of the memory; and 
 turning off generation of the internal clock during the second mode of operation of the memory. 
 
     
     
       28. The method of  claim 24 , wherein in the second mode of operation of memory, the resistance is disconnected from the node after a substantially fixed period of time has past after receipt of the active termination control signal. 
     
     
       29. The method of  claim 24 , wherein in the first mode of operation of memory, the connection of the resistance is initiated substantially in phase with a clock edge of the external clock. 
     
     
       30. The method of  claim 29 , wherein in the first mode of operation of memory, the disconnection of the resistance is initiated substantially in phase with the clock edge of the external clock. 
     
     
       31. The method of  claim 24 , wherein in the second mode of operation of memory, the initiation of the disconnection of the resistance is not correlated to a timing of a clock edge of the external clock. 
     
     
       32. The method of  claim 31 , wherein in the second mode of operation of memory, the initiation of the connection of the resistance is not correlated to a timing of the clock edge of the external clock. 
     
     
       33. The method of  claim 32 , wherein in the first mode of operation of the memory, the connection and disconnection of the resistance are initiated substantially in phase with clock edges of the external clock. 
     
     
       34. The method of  claim 24 , further comprising:
 storing data in a mode register of the memory; and 
 operating in the first mode of operation or in the second mode of operation in dependence on the data stored in the mode register. 
 
     
     
       35. A memory system comprising:
 a controller which generates an active termination control signal; and   a memory comprising:
 a node; and 
 a termination resistor which provides a termination resistance for the memory circuit, comprises a plurality of resistors which are selectively connected between the node and a reference voltage; and 
 a control circuit which receives the externally supplied active termination control signal, to synchronously switch on and off a connection of the node to the reference voltage through the termination resistor according to the active termination control signal in a first mode of operation of the memory, and to asynchronously switch the connection of the node to the reference voltage through the termination resistor according to the active termination control signal in a second mode of operation of the memory. 
   
     
     
       36. The memory system as claimed in claim 35, wherein the connection is switched on and off in synchronization with an external clock signal and in accordance with the active termination control signal in the first mode or the connection is switched on and off asynchronously with respect to the external clock signal in accordance with the active termination control signal in the second mode. 
     
     
       37. The memory system as claimed in claim 36, wherein the first mode is an active operation mode of the memory system and the second mode is a power down mode of the memory system. 
     
     
       38. The memory system as claimed in claim 37, wherein the memory further comprises a synchronization circuit for generating an internal clock signal, which is activated in the first mode and deactivated in the second mode. 
     
     
       39. The memory system as claimed in claim 38, wherein the synchronization circuit is one of a delay locked loop circuit and a phase locked loop circuit. 
     
     
       40. The memory system as claimed in claim 39, wherein the connection of the node to the reference voltage through the termination resistor is off when data is read from the memory system. 
     
     
       41. The memory system as claimed in claim 40, wherein, in the second mode, the connection of the node to the reference voltage through the termination resistor is switched on after a predetermined length of time after the active termination control signal is received. 
     
     
       42. The memory system as claimed in claim 41, wherein the predetermined length of time is does not vary in response to the external clock signal. 
     
     
       43. The memory system as claimed in claim 42, further comprising a mode register to store data used in determining the operation mode. 
     
     
       44. A memory system comprising:
 a controller which generates an active termination control signal; and   a memory comprising:
 a node connected to a terminal of the memory; 
 a termination resistor which provides a termination resistance for the memory and which is selectively connected between the node and a reference voltage; and 
 a control circuit which synchronously switches on and off the selective connection of the termination resistor between the node and the reference voltage according to the externally supplied active termination control signal when the memory circuit is in an active operational mode, and which asynchronously modifies the selective connection of the termination resistor between the node and the reference voltage according to the active termination control signal when the memory is in an asynchronous mode comprising at least one of a standby mode and a power down operational mode. 
   
     
     
       45. The memory system as claimed in claim 44, wherein the memory further comprises a synchronization circuit for generating an internal clock signal, which is activated in the active operational mode and deactivated in the asynchronous mode. 
     
     
       46. The memory system as claimed in claim 45, wherein the synchronization circuit is one of a delay locked loop circuit and a phase locked loop circuit. 
     
     
       47. The memory system as claimed in claim 46, wherein the selective connection of the termination resistor is disconnected when data is read from the memory circuit. 
     
     
       48. The memory system as claimed in claim 47, wherein in the asynchronous mode, the selective connection of the termination resistor is connected after a predetermined length of time after receipt of the active termination control signal. 
     
     
       49. The memory system as claimed in claim 48, the predetermined length of time is not proportional to a period of any received external clock signal. 
     
     
       50. The memory system as claimed in claim 44, wherein the termination resistor comprises:
 a first UP resistor which is selectively connected between the first reference voltage and the node in response to a first control signal; and   a second UP resistor which is selectively connected between the first reference voltage and the node in response to a second control signal.   
     
     
       51. The memory system as claimed in claim 50, wherein the termination resistor further comprises:
 a first DOWN resistor which is selectively connected between the second reference voltage and the node in response to a third control signal; and   a second DOWN resistor which is selectively connected between the second reference voltage and the node in response to a fourth control signal.   
     
     
       52. A memory system, comprising:
 a controller which generates an active termination control signal;   a semiconductor memory chip including a terminal, an input buffer connected to the terminal and a termination circuit connected the terminal, the termination circuit comprising:
 a node connected to the terminal of the memory chip; and 
 a termination resistor which provides a termination resistance for the memory chip, comprises a plurality of resistors which are selectively connected between the node and a reference voltage; and 
   a control circuit which receives the externally supplied active termination control signal, to synchronously switch on and off a connection of the node to the reference voltage through the termination resistor according to the active termination control signal in a first mode of operation of the memory chip, and to asynchronously switch the connection of the node to the reference voltage through the termination resistor according to the active termination control signal in a second mode of operation of the memory chip.   
     
     
       53. The memory system as claimed in claim 52, wherein the connection is switched on and off in synchronization with an external clock signal and in accordance with the active termination control signal in the first mode or the connection is switched on and off asynchronously with the external clock signal in accordance with the active termination control signal in the second mode. 
     
     
       54. A method of operating a memory system, comprising:
 generating an active termination control signal by a controller;   in a first mode of operation of the memory:
 receiving the active termination control signal; 
 in response to the receipt of the active termination control signal, switching on and off a connection of a resistance between a node and a reference voltage in synchronism with an external clock received by the memory, the node being connected to a terminal of the memory; and 
   in a second mode of operation of the memory:
 receiving the active termination control signal; 
 in response to the receipt of the active termination control signal, switching on and off the connection of the resistance between the node and the reference voltage independent of a switching timing of the external clock received by the memory. 
   
     
     
       55. The method of claim 54, wherein the second mode of operation comprises at least one from among a power down mode of operating the memory and a standby mode of operating the memory. 
     
     
       56. The method of claim 54, further comprising:
 generating an internal clock during the first mode of operation of the memory; and   turning off generation of the internal clock during the second mode of operation of the memory.   
     
     
       57. The method of claim 54, wherein in the second mode of operation of memory, the resistance is disconnected from the node after a substantially fixed period of time has passed after receipt of the active termination control signal. 
     
     
       58. The method of claim 54, wherein in the first mode of operation of memory, the connection of the resistance is initiated substantially in phase with a clock edge of the external clock. 
     
     
       59. The method of claim 58, wherein in the first mode of operation of memory, the disconnection of the resistance is initiated substantially in phase with the clock edge of the external clock. 
     
     
       60. The method of claim 54, wherein in the second mode of operation of memory, the initiation of the disconnection of the resistance is not correlated to a timing of a clock edge of the external clock. 
     
     
       61. The method of claim 60, wherein in the second mode of operation of memory, the initiation of the connection of the resistance is not correlated to a timing of the clock edge of the external clock. 
     
     
       62. The method of claim 61 wherein in the first mode of operation of the memory, the connection and disconnection of the resistance are initiated substantially in phase with clock edges of the external clock. 
     
     
       63. The method of claim 54, further comprising:
 storing data in a mode register of the memory; and   operating in the first mode of operation or in the second mode of operation in dependence on the data stored in the mode register.