Programmable logic integrated circuit devices with low voltage differential signaling capabilities
First Claim
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1. Buffer circuitry configured to produce from an input signal indicative of information a pair of output signals that indicate the information by the relative polarity of their voltages comprising:
- a source of relatively high voltage;
a source of relatively low voltage;
differential switching circuitry configured to produce the output signals in response to the input signal;
first resistor circuitry connected in series between the source of relatively high voltage and the differential switching circuitry; and
second resistor circuitry connected in series between the differential switching circuitry and the source of relatively low voltage, wherein;
connections between the sources, the differential switching circuitry, and the first and second resistor circuitries are such that when external circuitry is connected in series between the two output signals, current flows in series from the source of relatively high voltage through the first resistor circuitry, through the external circuitry, through the second resistor circuitry, to the source of relatively low voltage; and
at least one of the first and second resistor circuitries includes a transistor coupled in series with a first resistor and a second resistor and is configured to increase in resistance in response to an increase in voltage difference between the source of relatively high voltage and the source of relatively low voltage.
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Abstract
A programmable logic device is equipped for low voltage differential signaling (“LVDS”) by providing an LVDS input buffer and/or an LVDS output buffer on the device. I/O pins on the device that are used together in pairs for LVDS can alternatively be used individually for other types of signaling. The LVDS buffers are constructed to give good performance and to meet LVDS specifications despite variations due to temperature, manufacturing process inconsistency, and power supply changes.
28 Citations
16 Claims
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1. Buffer circuitry configured to produce from an input signal indicative of information a pair of output signals that indicate the information by the relative polarity of their voltages comprising:
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a source of relatively high voltage; a source of relatively low voltage; differential switching circuitry configured to produce the output signals in response to the input signal; first resistor circuitry connected in series between the source of relatively high voltage and the differential switching circuitry; and second resistor circuitry connected in series between the differential switching circuitry and the source of relatively low voltage, wherein; connections between the sources, the differential switching circuitry, and the first and second resistor circuitries are such that when external circuitry is connected in series between the two output signals, current flows in series from the source of relatively high voltage through the first resistor circuitry, through the external circuitry, through the second resistor circuitry, to the source of relatively low voltage; and at least one of the first and second resistor circuitries includes a transistor coupled in series with a first resistor and a second resistor and is configured to increase in resistance in response to an increase in voltage difference between the source of relatively high voltage and the source of relatively low voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for receiving an input signal indicative of information and for providing a pair of output signals on a pair of pins that indicate the information by the relative polarity of their voltages comprising:
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coupling a first of the two pins to a source of relatively high voltage via first resistor circuitry and coupling a second of the two pins to a source of relatively low voltage via second resistor circuitry when the input signal is at a first logic level; coupling the second of the two pins to the source of relatively high voltage via the first resistor circuitry and coupling the first of the two pins to the source of relatively low voltage via the second resistor circuitry when the input signal is at a second logic level; and configuring a transistor in one of the first and second resistor circuitries to increase in resistance in response to an increase in voltage difference between the source of relatively high voltage and the source of relatively low voltage, wherein said transistor is coupled in series with a first resistor and a second resistor. - View Dependent Claims (12, 13, 14, 15, 16)
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Specification