Methods and apparatus to DC couple LVDS driver to CML levels
AssigneeAltera Corporation
InventorsWilson Wong, Tim Hoang, Sergey Shumarayev, Rakesh Patel, Simardeep Maangat
Life of this patent
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Abstract
Circuitry and methods are provided for an LVDS-like transmitter that may be able to DC couple to a receiver having a CML termination scheme. Replacing the common mode voltage source of an LVDS transmitter with a resistive pulldown to ground may allow the transmitter to interface in a DC coupled fashion with a CML receiver. Further, the resistive pulldown may be programmable. This LVDS-like transmitter may be able to support a wider customer base by allowing it to DC couple to a wider range of termination voltage levels, such as CML termination voltage levels.
Claims20
Transmitter circuitry configured to DC couple to a receiver having a DC termination voltage level and a termination resistance, the transmitter circuitry comprising:
- a transmitter common mode node having a common mode voltage level;
- and
- a resistor circuit, having a variable resistance, connected between the transmitter common mode node and ground.
Transmitter circuitry configured to DC couple to a receiver, the transmitter circuitry comprising:
- a first transmitter current source coupled between a voltage source and a first termination resistor;
- a second transmitter current source coupled between a second termination resistor and ground;
- and
- a variable resistor coupled between the first and second termination resistors and ground.
A method for DC coupling transmitter circuitry to receiver circuitry having a DC termination voltage level and a DC termination resistance, the method comprising varying the resistance of a variable resistor circuit connected between a common mode node of the transmitter and ground.
Dependencies are inferred from the claim text.