input structures and topologies are provided for coupling a differential input into a first stage of a circuit, topology, or device. An input pin is coupled to an impedance divider that translates an input voltage to accommodate low input voltage levels, while not saturating an input differential pair. A termination pair with a center tap pin is further coupled to the input pins. The center tap facilitates coupling different termination configurations to the input signal. The topologies accommodate packaged devices that have at least three external pins, two pins for the coupling of a differential input signal, and a pin for the termination pair center tap.
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1. A method for coupling an input signal to a circuit, said method comprising
receiving an input signal according to a first voltage standard;
establishing a circuit input voltage proportional to the voltage of said input input signal using a voltage divider; and
coupling a center tap pin to a reference node, thereby terminating said input signal, wherein said reference node is chosen based on said first voltage standard.
17. A packaged integrated circuit comprising:
an integrated circuit comprising:
a first voltage divider having a first intermediate node and a second voltage divider having a second intermediate node; and
a termination pair comprising first and second resistors, wherein said first resistor is coupled to said first voltage divider and said second resistor is coupled to said second voltage divider; and
a package comprising said integrated circuit and
a first input pin coupled to said first voltage divider;
a second input pin coupled to said second voltage divider; and
a third input pin coupled to said first and second resistors.
8. A method for coupling a differential output signal according to a first logic standard to a circuit, said method comprising:
providing an integrated circuit comprising:
a first voltage divider having a first intermediate node and a second voltage divider having a second intermediate node; and
a termination pair comprising first and second resistors, wherein said first resistor
is coupled to said first voltage divider and said second resistor is coupled to said second voltage divider; and a center pin coupled to said first and second resistors;
coupling said differential output signal to said first and second intermediate nodes; and
coupling said center pin to a reference node, wherein the voltage at said reference node is chosen based on said logic standard.
0. 28. A structure comprising an integrated circuit encased in an integrated circuit package, the structure comprising:
a first pin and a second pin for receiving a differential input signal according to a first voltage standard;
a third pin, acting as a center tap pin, coupled to the first pin by a first termination resistance and coupled to the second pin by a second termination resistance, the first termination resistance and the second termination resistance being internal to the integrated circuit package, the third pin for being coupled to a reference node, wherein said reference node is chosen based on said first voltage standard,
wherein the third pin is directly connected to a junction between the first termination resistance and the second termination resistance such that there is no additional resistance between the third pin and the junction;
a differential amplifier internal to the integrated circuit package for receiving the input signal;
at least a fourth pin for outputting an output signal controlled by the input signal; and
a fifth pin of the integrated circuit package, the fifth pin receiving a reference voltage generated internal to the integrated circuit package, the fifth pin for being connected to the third pin as a reference voltage for ac coupled input signals.
0. 18. A method for coupling an input signal to a circuit, said method comprising
receiving the input signal according to a first voltage standard, the input signal being a differential input signal comprising an inverted input signal and a non-inverted input signal, the inverted input signal being applied to a first pin of an integrated circuit package, and the non-inverted signal being applied to a second pin of the integrated circuit package;
coupling a third pin of the integrated circuit package, acting as a center tap pin, to a reference node, thereby terminating said input signal, wherein said reference node is chosen based on said first voltage standard, the third pin being connected within the integrated circuit package to the first pin by a first termination resistance, the third pin also being connected within the integrated circuit package to the second pin by a second termination resistance,
wherein the third pin is directly connected to a junction between the first termination resistance and the second termination resistance such that there is no additional resistance between the third pin and the junction;
amplifying the input signal by a differential amplifier internal to the integrated circuit package;
outputting an output signal, controlled by the input signal, on at least a fourth pin of the integrated circuit package; and
providing at a fifth pin of the integrated circuit package a reference voltage generated internal to the integrated circuit package, the fifth pin for being connected to the third pin as a reference voltage for ac coupled input signals.
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16. A packaged integrated circuit according to
0. 19. A method according to claim 18, wherein said first voltage standard is CML, and said reference node is an open, or not connected, node.
0. 20. A method according to claim 18, wherein said first voltage standard is CML, said input signal is ac-coupled to said circuit, and said reference node is an ac reference node.
0. 21. A method according to claim 18, wherein said first voltage standard is PECL, and said reference node has a voltage (VCC-2V).
0. 22. A method according to claim 18, wherein said first voltage standard is PECL, said input signal is ac-coupled to said circuit, and said reference node is an ac reference node.
0. 23. A method according to claim 18, wherein said first voltage standard is LVDS, and said reference node is an open, or not connected, node.
0. 24. A method according to claim 18, wherein said first voltage standard is HSTL and said reference node is a ground node.
0. 25. A method according to claim 18 wherein the reference voltage generated at the fifth pin is nominally a supply voltage (Vcc) minus 1.4 volts.
0. 26. A method according to claim 18 wherein the first termination resistance is 50Ω, and the second termination resistance is 50Ω.
0. 27. A method according to claim 26 where the first termination resistance and the second termination resistance are resistors.
0. 29. A structure according to claim 28, wherein said first voltage standard is CML, and said reference node is an open, or not connected, node.
0. 30. A structure according to claim 28, wherein said first voltage standard is CML, said input signal is ac-coupled to said circuit, and said reference node is an ac reference node.
0. 31. A structure according to claim 28, wherein said first voltage standard is PECL, and said reference node has a voltage (VCC-2V).
0. 32. A structure according to claim 28, wherein said first voltage standard is PECL, said input signal is ac-coupled to said circuit, and said reference node is an ac reference node.
0. 33. A structure according to claim 28, wherein said first voltage standard is LVDS, and said reference node is an open, or not connected, node.
0. 34. A structure according to claim 28, wherein said first voltage standard is HSTL and said reference node is a ground node.
0. 35. A structure according to claim 28 wherein the reference voltage generated at the fifth pin is nominally a supply voltage (Vcc) minus 1.4 volts.
0. 36. A structure according to claim 28 wherein the first termination resistance is 50Ω, and the second termination resistance is 50Ω.
0. 37. A structure according to claim 36 where the first termination resistance and the second termination resistance are resistors.
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The present invention relates generally to input/output logic (“I/O”) interface technologies and more particularly to input structures having adaptable input voltage and termination levels.
A variety of input/output logic standards are in use today including Positive Emitter-Coupled Logic (PECL), Current-Mode Logic (CML), High Speed Transceiver Logic (HSTL), and Low Voltage Differential Signals (LVDS). These configurations may be AC-coupled or DC-coupled.
Each standard defines its own voltage level, type, and termination required for coupling with another stage, or another device. For example, PECL signals generally have voltage levels ranging from (VCC−900 mV) to (VCC−1.7V) where VCC represents a supply voltage. CML signals typically have a voltage level ranging from VCC to (VCC−400 mV). LVDS signals typically have voltage levels ranging from 1 to 1.4V, and HSTL signals typically have voltage levels ranging from 0.3V to 1.1V. Other signal types may use other voltage ranges.
Accordingly, driver devices need to adapt to a variety of input voltage levels and termination requirements to achieve compatibility. This is typically achieved using multiple input circuits, each able to couple with a particular standard, via a multiplexer. See, for example,
Thus, interfacing from one I/O technology, or standard, to another can therefore be a complex and difficult task. Translators and/or complex termination networks may be necessary for a given device to accept input from a variety of common standards.
Accordingly, there is a need in the art for an input structure that can receive an input according to any of a variety of common standards, including accepting input signals at a variety of voltage levels. Further, such an input structure should be able to provide a variety of termination schemes.
The present invention provides such an input structure.
One aspect of the present invention provides a method for coupling an input signal to a circuit. An input signal according to a first voltage standard is received, and an input voltage proportional to the voltage of the input signal is established using a voltage divider. A center tap pin is coupled to a reference node, where the reference node is chosen based on the voltage standard of the input signal, thereby terminating the input signal.
In another aspect of the present invention, a packaged integrated circuit is provided including an integrated circuit and a package. The integrated circuit includes a first and second voltage divider, each having an intermediate node, and further includes a termination pair. The termination pair includes a first and second resistor, where the first resistor is coupled to the first voltage divider, and the second resistor is coupled to the second voltage divider. The package includes a first input pin coupled to the first voltage divider, a second input pin coupled to the second voltage divider, and a center tap pin coupled to the first and second resistors.
The accompanying drawings, which are schematic in some instances and are incorporated in and form a part of this specification and, together with the description, serve to explain the principles of the invention and demonstrate one or more embodiments of the invention.
Input structures and topologies are provided for coupling a differential input to a first stage of a circuit, topology, or device. A pair of input pins is coupled to a divider impedance that translates an input voltage level to accommodate low input voltage levels, while not saturating an input differential pair of devices. A termination resistor pair with a center tap is further coupled to the input pins. The center tap facilitates coupling of different termination configurations to the input pins. In practice, packaged devices have at least three external pins, two pins for the coupling of a differential input signal, and one pin for the termination pair center tap.
One embodiment of an input structure according to the present invention is shown in
Voltage dividers 220 and 225, e.g. resistors 230, 232, 235, 237, are coupled between an input signal node and a power supply or other reference voltage, such as VCC 228. In a preferred embodiment, resistors 232 and 237 have a value of 1.5 kΩ while resistors 230 and 235 have a value of 1 kΩ. Intermediate nodes 240 and 245 of voltage divider 220 and 225 are coupled to a first input stage, here a differential pair. In
As noted, the embodiment of
In
Accordingly, input structures provided by the present invention comprise preferably three nodes, coupleable to external signals or devices. In the embodiment of
Input structures provided by the present invention find use in combination with a variety of circuit topologies and devices. Output taken from a first input stage, such as from the collector nodes of transistors 250 and 255 in the embodiment shown in
The foregoing descriptions of specific embodiments and best mode of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. For example, the above-described circuit topologies were coupled between a single VCC power supply and ground. As will be readily appreciated by those skilled in the art, embodiments of the present invention include circuit topologies coupled between ground a negative VSS power supply, between two power supplies, VCC and VSS, etc. Further, components of the present invention may be fully integrated with one another, or may merely be in functional communication with on another. Some or all components described above may be integrated on one or more semiconductor chips, for example, and other components bonded or otherwise brought into communication with the chip or chips. Further, some or all components described above may be packaged and integrated with methods known in the art, for example on printed circuit boards and the like.
While embodiments described above depicted input signal nodes 205 and 210, as appreciated by those skilled in the art, various devices or topologies may be coupled to or integrated to nodes 205 and 210 for providing a differential input signal including other devices, circuit topologies, single-to-double ended input converters, etc. Further, while voltage dividers 220 and 225 have been described in terms of two resistors each, voltage dividers 220 and 225 may comprise substantially any components, including resistors, transistors, capacitors, and inductors, such that an intermediate node of the voltage divider is coupled to an input stage in such a way that a voltage at the intermediate node is an appropriate voltage for coupling to the input stage.
The embodiments were chosen and described to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.
Wong, Thomas S., Pratt, Stephen J. B.
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