Dual-mode LVDS/CML transmitter methods and apparatus
AssigneeAltera Corporation
InventorsShoujun Wang, Yuming Tao, William Bereza, Tad Kwasniewski
Life of this patent
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Abstract
A dual-mode LVDS/CML transmitter allows a single circuit to operate as either an LVDS transmitter or a CML transmitter. The transmitter mode can be switched by activating or deactivating appropriate circuit elements, and changing the voltage or current produced by appropriate sources or sinks. This flexibility allows a single transmitter to operate well in both AC and DC coupling conditions, and facilitates interoperation with a greater variety of receivers.
Claims24
Transmitter circuitry configured to produce from a pair of input signals a pair of output signals, the transmitter circuitry comprising:
- a first voltage source;
- a second voltage source;
- a third voltage source;
- differential switching circuitry operative to produce the output signals in response to the input signals;
- and
- resistor circuitry coupled to the differential switching circuitry, wherein:
- a voltage of the first voltage source is higher than a voltage of the third voltage source;
- a voltage of the second voltage source is variable;
- and
- the transmitter circuitry is operative to select between:
- a) a first mode in which current is conducted from the first voltage source to the third voltage source, passing through the resistor circuitry and first and second portions of the switching circuitry, and
- b) a second mode in which current is conducted from the second voltage source to the third voltage source, passing through a portion of the resistor circuitry and the second portion of the switching circuitry without passing through the first portion of the switching circuitry.
A method of changing a mode of a transmitter circuit, the method comprising:
- changing the amount of voltage generated by a variable voltage supply;
- changing the amount of current generated by a variable current supply;
- and
- electrically decoupling the variable current supply from a voltage source, the variable voltage supply supplying its voltage to a first node in the transmitter circuit;
- and the voltage source, when not electrically decoupled, being electrically connected so that current can flow from the voltage source through the first node to the variable current supply.
Transmitter circuitry configured to produce from a pair of input signals a pair of output signals, the transmitter circuitry comprising:
- a first voltage source;
- a second voltage source;
- a third voltage source;
- differential switching circuitry operative to produce the output signals in response to the input signals;
- and
- resistor circuitry coupled to the differential switching circuitry, wherein:
- a voltage of the first voltage source is higher than a voltage of the third voltage source;
- a voltage of the second voltage source is variable;
- and
- the transmitter circuitry is operative to select between:
- a) a first mode in which the output signals are transmitted using a low voltage differential signaling (LVDS) transmission standard;
- and
- b) a second mode in which the output signals are transmitted using a current mode logic (CML) transmission standard.
Dependencies are inferred from the claim text.