Low voltage differential swing interconnect buffer circuit
First Claim
1. An integrated circuit that includes a low voltage differential swing interconnect buffer and biasing circuit for data transmission over first and second balanced transmission lines having a terminating resistor of a first resistance;
- said integrated circuit connected to a reference resistance;
said interconnect buffer and basing circuit comprising;
an output buffer connected to said transmission lines and comprising a first voltage controlled current source having a first bias voltage and being connected to a first supply voltage, a first voltage controlled current sink having a second bias voltage and being connected to ground, and a current switch being connected in series between said first voltage controlled current source and said first voltage controlled current sink, said current switch controlling the direction of current flow from said output buffer and through said first and second balanced transmission lines and terminating resistor;
an input buffer comprising a first voltage controlled input resistor having a third bias voltage and a comparator for detecting the polarity of a voltage drop across said voltage controlled input resistor when input current flows through it;
a first voltage reference circuit having high and low input reference voltages and being connected to said reference resistance, said first voltage reference circuit generating said first and second bias voltages such that current from said output buffer through said first and second transmission lines generates a voltage drop across said terminating resistor substantially from said high input reference voltage to said low input reference voltage; and
a second voltage reference circuit having as an input said first and second bias voltages and at least one of said input reference voltages, said second voltage reference circuit generating said third bias voltage to bias said first voltage controlled resistor in said input buffer to a resistance substantially equal to said first resistance.
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Accused Products
Abstract
A low voltage differential swing interconnect I/O buffer within an output buffer part comprising a voltage controlled current source, voltage controlled current sink, and a current switch and an input buffer part comprising a voltage controlled resistance. The output current and input resistance of the I/O buffer is determined by biasing voltages which are generated by on-chip reference circuits and applied to the voltage controlled components of the I/O buffer. Using two input reference voltages and a single reference resistor, the reference circuits dynamically adjust the biasing voltages so that the I/O buffer maintains the required output current and input resistance for all manufacturing process, supply voltage, and chip temperature variations.
143 Citations
55 Claims
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1. An integrated circuit that includes a low voltage differential swing interconnect buffer and biasing circuit for data transmission over first and second balanced transmission lines having a terminating resistor of a first resistance;
- said integrated circuit connected to a reference resistance;
said interconnect buffer and basing circuit comprising; an output buffer connected to said transmission lines and comprising a first voltage controlled current source having a first bias voltage and being connected to a first supply voltage, a first voltage controlled current sink having a second bias voltage and being connected to ground, and a current switch being connected in series between said first voltage controlled current source and said first voltage controlled current sink, said current switch controlling the direction of current flow from said output buffer and through said first and second balanced transmission lines and terminating resistor; an input buffer comprising a first voltage controlled input resistor having a third bias voltage and a comparator for detecting the polarity of a voltage drop across said voltage controlled input resistor when input current flows through it; a first voltage reference circuit having high and low input reference voltages and being connected to said reference resistance, said first voltage reference circuit generating said first and second bias voltages such that current from said output buffer through said first and second transmission lines generates a voltage drop across said terminating resistor substantially from said high input reference voltage to said low input reference voltage; and a second voltage reference circuit having as an input said first and second bias voltages and at least one of said input reference voltages, said second voltage reference circuit generating said third bias voltage to bias said first voltage controlled resistor in said input buffer to a resistance substantially equal to said first resistance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
- said integrated circuit connected to a reference resistance;
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23. An integrated circuit that includes a differential swing interconnect I/O buffer comprising an output buffer and an input buffer;
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said input buffer having first and second inputs and comprising a first variable input resistor having resistance determined by a resistor control voltage and being connected between said first and second inputs and to an input detector circuit for detecting the polarity of a voltage drop across said variable input resistor; said output buffer having first and second outputs and comprising a first output buffer part connected between a power supply and said first and second outputs and a second output buffer part connected between ground and said first and second outputs; said first output buffer part comprising a first variable current source controlled by a source bias voltage and a first group of switches configurable as conducting or non-conducting, said first variable current source and said first group of switches being series-connected between said power supply and said first and second outputs; said second output buffer part comprising a first variable current sink controlled by a sink bias voltage and a second group of switches configurable as conducting or non-conducting, said first variable current sink and said second group of switches being series-connected between ground and said first and second outputs; and an output control circuit connected to said first and second groups of switches which controls the state of said switches to thereby define a first switch configuration wherein said first output is connected to said current source and said second output is connected to said current sink and a second switch configuration wherein said first output is connected to said current sink and said second output is connected to said current source; and wherein said first input is connected to said first output and said second input is connected to said second output.
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24. An integrated circuit that includes a differential swing interconnect I/O buffer comprising an output buffer and an input buffer;
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said input buffer having first and second inputs and comprising a first variable input resistor having resistance determined by a resistor control voltage and being connected between said first and second inputs and to an input detector circuit for detecting the polarity of a voltage drop across said variable input resistor; said output buffer having first and second outputs and comprising a first output buffer part connected between a power supply and said first and second outputs and a second output buffer part connected between ground and said first and second outputs; said first output buffer part comprising a first variable current source controlled by a source bias voltage and a first group of switches configurable as conducting or non-conducting, said first variable current source and said first group of switches being series-connected between said power supply and said first and second outputs; said second output buffer part comprising a first variable current sink controlled by a sink bias voltage and a second group of switches configurable as conducting or non-conducting, said first variable current sink and said second group of switches being series-connected between ground and said first and second outputs; and an output control circuit connected to said first and second groups of switches which controls the state of said switches to thereby define a first switch configuration wherein said first output is connected to said current source and said second output is connected to said current sink and a second switch configuration wherein said first output is connected to said current sink and said second output is connected to said current source; said integrated circuit being connected to a reference resistor and further including a current bias reference circuit which generates said source bias voltage and said sink bias voltage, said current bias reference circuit being connected to a high input reference voltage and a low input reference voltage and comprising; a first current bias reference circuit part connected between said power supply and said reference resistor at a first reference node and comprising a second variable current source controlled by said source bias voltage; a second current bias reference circuit part connected between ground and said reference resistor at a second reference node and comprising a second variable current sink controlled by said sink bias voltage; and a first feedback circuit that generates said source bias voltage with magnitude such that the voltage at said first reference node is substantially equal to said high input reference voltage and that generates said sink bias voltage with magnitude such that the voltage at said second reference node is substantially equal to said low input reference voltage, said first feedback circuit being connected so that the magnitude of the current through said second variable current source is inversely dependent on the voltage at said first reference node and the magnitude of the current through said second variable current sink is dependent on the voltage at said fourth node. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45)
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46. A current biasing circuit that generates bias voltages for a plurality of current sources and generates a controlled voltage and current at two points, said current biasing circuit comprising:
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a first voltage controlled current source series connected between a supply voltage and a reference resistor at a first node; a first voltage controlled current sink series connected between ground and said reference resistor at a second node; a first feedback circuit having inputs connected to a first reference voltage and said first node and having an output connected to said first voltage controlled current source, whereby said first feedback circuit biases said first voltage controlled current source so that the voltage at said first node is substantially equal to said first reference voltage; and a second feedback circuit having inputs connected to a second reference voltage and said second node and having an output connected to said first voltage controlled current sink, whereby said second feedback circuit biases said first voltage controlled current sink so that the voltage at said second node is substantially equal to said second reference voltage. - View Dependent Claims (47, 48, 49, 50, 51, 52, 53, 54, 55)
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Specification