Self-terminating data line driver

Abstract

The invention is a self-terminating helper flip-flop buffer circuit pertinent to a dynamic random access memory (DRAM) or static random access memory (SRAM) device. The invention turns off a device which is sourcing current to pull the data line low. The device is turned off when the potential on the low data line has transitioned to the trip point of the output data latch. The circuit of the invention senses the transition and provides the self terminating signal to the current source.

I claim: 
     
       1. An electronic device for driving differential potentials to first and second data lines, comprising: a) a first node connectable to a first potential;   b) a second node;   c) a gating device electrically interposed between said first node and said second node;   d) a first switching device interposed between said first data line and said second node;   e) a second switching device interposed between said second data line and said second node, said first data line capable of being pulled toward said first potential when said first switching device is actuated, and said second data line capable of being pulled toward said first potential when said second switching device is actuated; and   f) a differential signal sensing circuit for sensing said differential potentials on said first and second data lines, said first and second data lines in electrical communication with first and second input terminals, respectively, of said differential signal sensing circuit, said differential signal sensing circuit having an output terminal, a control input of said gating device in electrical communication with said output terminal of said signal sensing circuit, said gating device having first and second switching states controlled by an output signal from said differential signal sensing circuit, said output signal available at said output terminal, wherein said differential potentials can be driven to said first and second data lines when said gating device has said first switching state and wherein the driving of said differential potentials is inhibited when said gating device has said second switching state, said gating device capable of attaining said second switching state when one of said first and second data lines has a potential equal to a trip point of said differential signal sensing circuit, said trip point determined by electrical characteristics of said differential signal sensing circuit.     
     
     
       2. The electronic device as specified in claim 1, further comprising a current source in serial connection with said second node and said gating device, wherein a potential on one of said first and second data lines is capable of being pulled toward said first potential to a substantially greater degree than a potential on a remaining one of said first and second data lines, said pulling effected when a respective one of said first and second switching devices is actuated, said respective one data line pulled toward said first potential through said current source and said gating device, said gating device terminating the pulling of said one data line toward said first potential by interrupting a current path between said first potential and said current source when the potential of said one data line is equal to said trip point of said differential signal sensing circuit. 
     
     
       3. The electronic device as specified in claim 2, comprising: a) first and second cross-coupled transistors coupled at a common input terminal, wherein a signal at an output node of said second cross-coupled transistor provides a gate signal for said first switching device and said first cross-coupled transistor, and wherein a signal at an output node of said first cross-coupled transistor provides a gate signal for said second switching device and said second cross-coupled transistor;   b) first and second input/output lines accepting electronic information to be driven to said first and second data lines respectively, wherein said electronic information provides said differential potential;   c) a decode switching device interposed between each of said output nodes of said first and second cross-coupled transistors and a corresponding one of said first and second input/output lines;   d) equilibrate circuitry capable of providing an equilibrate potential to said output nodes of said first and second cross-coupled transistors, said first and second cross-coupled transistors in electrical communication alternately with said first and second input/output lines and said equilibrate circuitry, said equilibrate potential on said output nodes of said first and second cross-coupled transistors providing a signal for deactuating said first and second switching devices;   e) a third switching device electrically interposed between a third node connectable to a second potential and said common input terminal, said third switching device, when activated, allowing said output nodes of said first and second cross-coupled transistors to be pulled to said equilibrate potential, and when said decode switching devices are actuated allowing said output nodes of said first and second cross-coupled transistors to be pulled to said differential potentials, said differential potentials amplified at said output nodes of said first and second cross-coupled transistors, said differential potentials, on said output nodes, providing a signal to actuate one of said first and second switching devices while providing a signal to deactuate the remaining one of said first and second switching devices in order to allow said first and second data lines to attain said differential potentials.   
     
     
       4. The electronic device as specified in claim 3, further comprising a timing enable signal for enabling said differential signal sensing circuit by activating said third switching device and said current source. 
     
     
       5. The electronic device a specified in claim 4, wherein said differential signal sensing circuit further comprises two cross-coupled logic gates, a first logic gate having first, second, and third input terminals and a second logic gate having first and second input terminals, said first and second input terminals of said first logic gate in electrical communication with said first and second data lines respectively and said third input terminal in electrical communication with an output terminal of said second logic gate, said first input of said second logic gate in electrical communication with an output of said first logic gate, and said second input of said second logic gate accepting said timing enable signal, said output terminal of said second logic gate being said output terminal of said differential signal sensing circuit. 
     
     
       6. A method for driving differential potentials to data lines comprising: a) providing the differential potentials at input/output lines;   b) equilibrating transfer nodes to an equilibrate potential;   c) isolating said transfer nodes from said equilibrate potential;   d) allowing said transfer nodes to attain the differential potentials from said input/output lines;   e) driving said differential potentials to said data lines in response to said differential potentials on said transfer nodes;   f) sensing said differential potentials on the data lines with a sense circuit;   g) actuating a gating device with an output from said sense circuit;   h) deactuating said gating device when a potential on one of said data lines has a potential equal to a trip point of said sense circuit; and   i) interrupting a current flow at at least one of said data lines in response to said deactuating thereby terminating the driving of said differential potentials to said data lines.   
     
     
       7. The method as specified in claim 6, wherein said step of driving further comprises: a) enabling helper circuitry to facilitate a development of the differential potentials on said transfer nodes;   b) actuating a current source;   c) providing opposite gating signals to first and second driver transistors with said differential potentials on said transfer nodes, such that one of said driver transistors is actuated and the remaining one of said driver transistors is deactuated; and   d) pulling the data line in electrical communication with the actuated driver transistor to a potential equal to said trip point through said actuated gating device and said actuated current source.   
     
     
       8. A memory circuit for driving a potential to a first data line, and for determining a logic state of the potential on the first data line from a potential on a first information line, and for driving a potential to a second data line, and for determining a logic state of the potential on the second data line by a potential on a second information line, the circuit comprising: a) a reference node connectable to a reference potential;   b) a current source electrically interposed between said reference node and a junction node;   c) a first switching device electrically interposed between said first data line and said junction node;   d) a second switching device electrically interposed between said second data line and said junction node;   e) a helper flip flop electrically interposed said reference node and said first and said second information lines, said helper flip flop having a first control node in electrical communication with said first information line and having a second control node in electrical communication with said second information line, a potential on said first control node controlling an activation and deactivation of said second switching device, and a potential on said second control node controlling an activation and deactivation of said first switching device, said helper flip flop increasing a differential potential existing between said first and said second information lines such that in a first case said first control node has potential having a value which activates said second switching device and such that said second control node has a potential having a value which deactivates said first switching device, wherein said first data line is isolated from said current source by a deactivated said first switching device, such that in a second case said second control node has a potential having a value which activates said first switching device and such that said first control node has a potential having a value which deactivates said second switching device, wherein said second data line is isolated from said current source by a deactivated said second switching device;   f) a control latch circuit having a first and a second input node and having an output node, said first input node in electrical communication with said first data line and said second input node in electrical communication with said second data line, said control latch having a trip point, said trip point equal to a potential which alters a logic state of a potential at said output node; and   g) a terminating device, having a control input in electrical communication with said output node, said terminating device electrically interposed between said junction node and said reference node and in electrical communication with said current source, said control latch circuit generating an output signal at said output node for activating said terminating device during a separation of potentials on said first and second data lines and in response to said potentials on said first and said second data line is pulled toward said reference potential through said current source, said second switching device and said terminating device, said control latch circuit generating a terminating signal for deactivating said terminating device when said second data line reaches a potential equal to said trip point of said control latch circuit, and wherein in said second case said first data line is pulled toward said reference potential through said current source, said first switching device and said terminating device, said control latch circuit generating a terminating signal for deactivating said terminating device when said first data line reaches a potential equal to said trip point of said control latch circuit, said separation of potentials ceasing in response to said terminating signal deactivating said terminating device such that a differential potential between said first and said second data lines is limited to a maximum value equal to a difference in said potential on said first data line and said potential of said trip point in said first case, and equal to a difference in said potential on said second data line and said potential of said trip point in said second case.   
     
     
       9. A method for limiting a differential potential between a first data line and a second data line, the method comprising the following steps: a) driving a potential of the first data line toward a potential having a first logic state, said first logic state determined from a potential of a first information line;   b) driving a potential of the second data line toward a potential having a second logic state, said second logic state determined from a potential of a second information line;   c) monitoring said potentials on the first and the second data lines;   d) generating a terminating signal in response to one of said potentials of said first and said second data lines reaching a critical potential; and   e) terminating said step of driving said potential of said one of said first and said second data lines having said critical potential thereby limiting the differential potential between said first and said second data lines to a maximum value.   
     
     
       10. A method for driving a first data line to a first potential and a second data line to a second potential such that a differential potential exists between the first and the second data lines, comprising the following steps: a) precharging the first and the second data lines to a data line precharge potential;   b) precharging the first and second information lines to an information line precharge potential;   c) releasing the data line precharge potential in order to allow said first data line to attain said first potential and in order to allow said second data line to attain said second potential;   d) releasing the information line precharge potential in order to allow the first and the second information lines to attain potentials other than said information precharge potential;   e) developing a differential potential between a first I/O potential on the first information line and a second I/O potential on the second information line;   f) coupling said first I/O potential to a first control node;   g) coupling said second I/O potential to a second control node;   h) increasing a differential potential between said first and said second control nodes;   i) discharging the potential of said second data line through a discharge source to decrease a potential on said second data line in response to the potential on said first control node;   j)prohibiting said first data line from discharging in response to the potential on said second control node;   k) coupling said first data line to a potential having a logic state of a potential of said first information line;   l) monitoring the first and second data line potentials;   m) isolating said second data line from said discharge source in response to the potential of said second data line reaching a critical value; and   n) terminating said step of discharging said second data line in response to said step of isolating thereby limiting the differential potential between said first and said second data lines to a maximum value.   
     
     
       11. A memory circuit, comprising: a) a first data line for accepting data;   b) a first switching device in electrical communication with said first data line;   c) a second data line for accepting a complement of the data;   d) a second switching device in electrical communication with said second data line;   e) a coupling node coupling said first and said second switching devices;   f) a third switching device interposed between said coupling node and a reference node, said reference node capable of connection to an electrical potential, said first data line driven to said electrical potential of said reference node through said first switching device and said third switching device, and said second data line driven to said electrical potential of said reference node through said second switching device and said third switching device; and   g) a sensing and termination circuit in electrical communication with said first data line, said second data line, and a control input of said third switching device, said sensing and termination circuit sensing a value of a potential on said first data line and sensing a value of a potential on said second data line, said sensing and termination circuit generating a termination signal to said control input of said third switching device when one of said values reaches a trip point potential of said sensing and termination circuit, said termination signal deactuating said third switching device to electrically isolate said coupling node from said reference node thereby terminating the driving of said electrical potential of said reference node to one of said first and second data lines. .Iadd.   
     
     
       12.  An electronic device for driving a differential potential between first and second data lines, the electronic device comprising: a gating device for selectively conducting a first potential in response to a control signal;   a first switching device interposed between said first data line and said gating device for receiving said first potential and selectively conducting it to said first data line to pull said first data line toward said first potential;   a second switching device interposed between said second data line and said gating device for receiving said first potential and selectively conducting it to said second data line to pull said second data line toward said first potential; and   a differential signal sensing circuit coupled to said gating device for selectively providing said control signal thereto in response to a differential potential sensed by said sensing circuit between said first and second data lines in order to control the extent to which said first and second data lines are pulled toward said first potential. .Iaddend..Iadd.13. The electronic device as specified in claim 12, further comprising a current source in serial connection between said switching   
     
     
        devices and said gating device. .Iaddend..Iadd.14.  The electronic device as specified in claim 12, further comprising: first and second cross-coupled transistors coupled at a common input terminal, wherein a signal at an output node of said second cross-coupled transistor provides a gate signal for said first switching device and said first cross-coupled transistor, and wherein a signal at an output node of said first cross-coupled transistor provides a gate signal for said second switching device and said second cross-coupled transistor;   first and second input/output lines accepting electronic information to be driven to said first and second data lines, respectively, wherein said electronic information provides said differential potential;   a decode switching device interposed between each of said output nodes of said first and second cross-coupled transistors and a corresponding one of said first and second input/output lines;   equilibrate circuitry capable of providing an equilibrate potential to said output nodes of said first and second cross-coupled transistors, said equilibrate potential providing a signal for deactuating said first and second switching devices; and   a third switching device electrically interposed between a second potential and said common input terminal of said cross-coupled transistors. .Iaddend..Iadd.15. The electronic device as specified in claim 12, wherein said differential signal sensing circuit further comprises first and second logic gates, the first logic gate having first, second, and third input terminals and the second logic gate having first and second input terminals, said first and second input terminals of said first logic gate in electrical communication with said first and second data lines, respectively, and said third input terminal in electrical communication with an output terminal of said second logic gate, said first input terminal of said second logic gate in electrical communication with an output terminal of said first logic gate, and said second input terminal of said second logic gate accepting a timing enable signal, said output terminal of said second logic gate selectively providing said control   
     
     
        signal. .Iaddend..Iadd.16.  A method for driving a differential potential between data lines, the method comprising: providing the differential potential between input/output lines;   equilibrating transfer nodes to an equilibrate potential;   isolating said transfer nodes from said equilibrate potential;   applying said differential potential between said transfer nodes from said input/output lines;   driving said differential potential between said data lines in response to said differential potential being between said transfer nodes;   sensing said differential potential between said data lines; and   when the differential potential between said data lines equals a trip point potential, terminating the driving of said differential potential between said data lines, the trip point potential being selected to limit the differential potential driven between said data lines. .Iaddend..Iadd.17. The method as specified in claim 16, wherein said step of driving further comprises:   enabling helper circuitry to facilitate a development of the differential potential between said transfer nodes;   actuating a current source;   providing opposite gating signals to first and second driver transistors with said differential potential between said transfer nodes such that one of said driver transistors is actuated and the remaining one of said driver transistors is non-actuated; and   pulling the data line in electrical communication with the actuated driver transistor to a potential corresponding to said trip point potential through said actuated gating device and said actuated current source.   
     
     
        .Iaddend..Iadd.18.  A memory circuit for driving a potential to a first data line, and for determining a logic state of the potential on the first data line from a potential on a first information line, and for driving a potential to a second data line, and for determining a logic state of the potential on the second data line by a potential on a second information line, the circuit comprising: a current source connectable to a reference potential;   a first switching device electrically interposed between said first data line and said current source for selectively conducting current therebetween;   a second switching device electrically interposed between said second data line and said current source for selectively conducting current therebetween;   a helper flip flop having a first control node in electrical communication with said first information line and having a second control node in electrical communication with said second information line, a potential on said first control node controlling said second switching device and a potential on said second control node controlling said first switching device, said helper flip flop increasing a differential potential imposed between said first and second control nodes from a differential potential existing between said first and second information lines such that one of said first and second switching devices is active and the other is substantially inactive;   a control latch circuit in electrical communication with said first and second data lines for generating an output signal to initiate and effect a separation of potentials on said first and second data lines and for generating a terminating signal in response to a potential on one of said first and second data lines passing a trip point of said control latch circuit; and   a terminating device in electrical communication with said control latch circuit for receiving said output and terminating signals, said terminating device electrically interposed between said current source and said reference potential for conducting current therebetween in response to said output signal and for interrupting said conduction in response to said terminating signal such that a differential potential between said first and said second data lines is limited to a maximum value. .Iaddend..Iadd.19. A method for limiting a differential potential between a first data line and a second data line, the method comprising the following steps:   driving a potential of the first data line toward a potential having a first logic state, said first logic state determined from a potential of a first information line;   driving a potential of the second data line toward a potential having a second logic state, said second logic state determined from a potential of a second information line;   monitoring said potentials on the first and the second data lines; and   in response to one of said potentials of said first and said second data lines reaching a threshold potential, terminating said step of driving said potential of said one of said first and said second data lines having said threshold potential to limit the differential potential between said   
     
     
        first and said second data lines to a maximum value. .Iaddend..Iadd.20.  A method for driving a first data line to a first potential and a second data line to a second potential such that a differential potential exists between the first and the second data lines, comprising the following steps: precharging the first and the second data lines to a data line precharge potential;   precharging first and second information lines to an information line precharge potential;   releasing the data line precharge potential to enable said first data line to attain said first potential and to enable said second data line to attain said second potential;   releasing the information line precharge potential to enable the first and the second information lines to attain potentials other than said information precharge potential;   developing a differential potential between a first I/O potential on the first information line and a second I/O potential on the second information line;   coupling said first I/O potential to a first control node;   coupling said second I/O potential to a second control node;   increasing a differential potential between said first and said second control nodes;   altering the potential of said second data line through a current path to alter a potential on said second data line in response to the potential on said first control node;   substantially prohibiting said first data line from altering its potential in response to the potential on said second control node;   coupling said first data line to a potential having a logic state of a potential of said first information line; and   isolating said second data line from said current path in response to the potential of said second data line reaching a critical value, thereby limiting the differential potential between said first and said second   
     
     
        data lines to a maximum value. .Iaddend..Iadd.21.  A memory circuit, comprising: a first data line for accepting data;   a first switching device in electrical communication with said first data line;   a second data line for accepting a complement of the data;   a second switching device in electrical communication with said second data line;   a third switching device interposed between said first and second switching devices and a reference potential, said first data line adapted to be driven to said reference potential through said first switching device and said third switching device, and said second data line adapted to be driven to said reference potential through said second switching device and said third switching device; and   a sensing and termination circuit in electrical communication with said first data line, said second data line, and a control input of said third switching device for sensing a value of a potential on said first data line and sensing a value of a potential on said second data line, said sensing and termination circuit adapted to generate a termination signal to said control input of said third switching device when one of said values reaches a trip point potential of said sensing and termination circuit, said termination signal for deactuating said third switching device to electrically isolate said first and second data lines from said reference potential to terminate the driving of said reference potential   
     
     
        to one of said first and second data lines. .Iaddend..Iadd.22.  A method for driving differential potentials to data lines, the method comprising: equilibrating the data lines to an equilibrate potential;   isolating the data lines from the equilibrate potential;   providing the differential potentials at input/output lines;   transferring the differential potentials to the data lines;   sensing potentials on the data lines; and   when the sensed potential on one of the data lines equals a trip point potential, terminating the transferring of the differential potential thereto to limit a difference between the potentials on the data lines. .Iaddend..Iadd.23. A circuit for pulling a first conductor's potential closer to a target potential than a second conductor's potential without exceeding a maximum difference in potentials between the conductors, the circuit comprising:   a gating device for selectively conducting the target potential;   first and second switching devices coupled to the gating device for selectively conducting the target potential to the first and second conductors, respectively, the second switching device being substantially inactive when the first switching device is active; and   a differential signal sensing circuit coupled to the gating device for directing the gating device to isolate the switching devices from the target potential when the potential on one of the conductors passes a trip point of the sensing circuit and for otherwise generally directing the gating device to conduct the target potential to the switching devices, the trip point being selected to limit a difference in potentials between the conductors to a maximum. .Iaddend..Iadd.24. The circuit of claim 23   
     
     
        wherein the gating device comprises a MOS transistor. .Iaddend..Iadd.25. The circuit of claim 23 wherein the first and second switching devices are coupled to one another as a differential pair of switching devices. .Iaddend..Iadd.26. The circuit of claim 23 wherein the first and second switching devices each comprise a MOS transistor. .Iaddend..Iadd.27. The circuit of claim 23 wherein the differential signal sensing circuit comprises a latch set by a set signal to direct the gating device to conduct the target potential to the switching devices and reset when the potential on one of the conductors passes a trip point of the latch to direct the gating device to isolate the switching devices from the target potential. .Iaddend..Iadd.28. The circuit of claim 23 wherein the differential signal sensing circuit comprises a pair of cross-coupled NAND gates. .Iaddend..Iadd.29. The circuit of claim 23 further comprising equilibrate circuitry coupled to the first and second conductors for pre-charging and equalizing the potentials on the conductors to a supply 
     
     
        potential. .Iaddend..Iadd.30.  A buffer in a memory device interposed between first and second input/output lines and first and second data lines, the buffer comprising: a helper flip-flop for outputting first and second complimentary latched outputs in response to receiving a data signal and its compliment signal from the first and second input/output lines, respectively;   a gating device for selectively conducting a target potential;   a first switching device coupled to the helper flip-flop and the gating device for selectively conducting the target potential to the first data line in response to the helper flip-flop's second latched output;   a second switching device coupled to the helper flip-flop and the gating device for selectively conducting the target potential to the second data line in response to the helper flip-flop's first latched output; and   a differential signal sensing circuit coupled to the gating device for directing the gating device to isolate the switching devices from the target potential when a potential on one of the data lines passes a trip point of the sensing circuit and for otherwise generally directing the gating device to conduct the target potential to the switching devices, the trip point being selected to limit a difference in potentials between the data lines to a maximum so that the data signal and its compliment signal may be transferred from the input/output lines to the data lines while limiting the difference in potentials between the data lines. .Iaddend..Iadd.31. The buffer of claim 30 wherein the helper flip-flop comprises a pair of cross-couple MOS transistors. .Iaddend..Iadd.32. The buffer of claim 30 further comprising transfer circuitry coupled to the helper flip-flop for providing the data signal and its compliment signal thereto from the first and second input/output lines in response to a   
     
     
        transfer signal. .Iaddend..Iadd.33.  The buffer of claim 32 wherein the transfer circuitry comprises first and second transfer MOS transistors selectively coupling the first and second input/output lines, respectively, to the helper flip-flop in response to the transfer signal. .Iaddend..Iadd.34. The buffer of claim 30 further comprising equilibrate circuitry coupled to the first and second data lines for pre-charging and equalizing the potentials on the data lines to a supply potential. .Iaddend..Iadd.35. A circuit for pulling a conductor's potential to a selected potential between a reference potential and a supply potential, the circuit comprising: a gating device for selectively conducting one of the reference and supply potentials;   a switching device coupled to the gating device for selectively conducting the one of the reference and supply potentials to the conductor; and   a sensing circuit coupled to the gating device for directing the gating device to isolate the switching device from the one of the reference and supply potentials when the conductor's potential passes a trip point of the sensing circuit selected to limit the conductor's potential to the selected potential and for otherwise generally directing the gating device to conduct the one of the reference and supply potentials to the switching device. .Iaddend..Iadd.36. The circuit of claim 35 wherein the sensing circuit comprises a latch set by a set signal to direct the gating device to conduct the one of the reference and supply potentials to the switching device and reset when the conductor's potential passes a trip point of the latch to direct the gating device to isolate the switching device from the   
     
     
        one of the reference and supply potentials. .Iaddend..Iadd.37.  A method for pulling a conductive line's potential to a selected potential between a reference potential and a supply potential, the method comprising: selectively coupling the conductive line to one of the reference and supply potentials;   sensing the conductive line's potential; and   when the sensed potential equals the selected potential, isolating the conductive line from the one of the reference and supply potentials. .Iaddend.