Low power CMOS LVDS driver
View Patent ↗A low voltage CMOS output driver is adapted to generate an output voltage that stays within predefined limits at relatively low supply voltages. The output driver includes, in part, a voltage-controlled resistor, a voltage-controlled current sink, and a switching stage. A control circuit provides the voltages that are applied to the voltage-controlled resistor and the voltage-controlled current sink. The voltage applied to the voltage-controlled resistor defines the high output voltage. The voltage applied to the voltage-controlled current sink defines the low output voltage. The control circuit is a scaled replica of the output driver and is adapted to consume a current that is 1/L times the current consumed by the output driver.
1. An output driver comprising:
a voltage-controlled resistor;
a voltage-controlled current sink; and
a switching stage disposed between the voltage-controlled resistor and the voltage-controlled current sink and adapted to generate an output voltage across an external load said output voltage to vary between first and second output voltages, wherein the resistance of said voltage-controlled resistor is controlled by a first operational amplifier and the current through the voltage-controlled current sink is controlled by a second operational amplifier wherein said switching stage further comprises:
a first resistor having a first terminal coupled to a first terminal directly of the voltage-controlled resistor and a second terminal directly coupled to a first output node;
a first transistor having a first terminal coupled to the first output node, a second terminal coupled to a first terminal of the voltage-controlled current sink, and a third terminal coupled to a first input voltage;
a second transistor having a first terminal coupled to a second output node, a second terminal coupled to the first terminal of the voltage-controlled current sink, and a third terminal coupled to a second input voltage; and
a third transistor having a first terminal coupled to the first terminal of the voltage-controlled resistor, a second terminal coupled to the second output node, and a third terminal coupled to the second input voltage.
2. The output driver of claim 1 wherein said voltage-controlled current sink is a transistor having a gate terminal adapted to receive the output voltage of the second operational amplifier and a source terminal that is coupled to the ground.
3. The output driver of claim 2 wherein the first and second operational amplifier are disposed in a control circuit further comprising:
a second voltage-controlled resistor having a resistance that is adapted to vary in response to the output voltage of the first operational amplifier; and
a second voltage-controlled current sink configured to sink a current that is adapted to vary in response to the output voltage of the second operational amplifier.
4. The output driver of claim 3 wherein the current flowing through the first voltage-controlled current sink is L times the current flowing through the second voltage-controlled current sink, wherein L is a variable greater than or equal to one.
5. The output driver of claim 3 wherein the control circuit further comprises:
a second resistor having a first terminal coupled to the second voltage-controlled resistor, and a second terminal coupled to a positive terminal of the first operational amplifier, wherein the negative terminal of the operational amplifier is coupled to a first voltage supply; and
a third resistor having a first terminal coupled to the positive terminal of the first operational amplifier and a second terminal coupled to the positive terminal of the second operational amplifier; wherein the negative terminal of the operational amplifier is coupled to a second voltage supply, wherein said first and second voltage supplies define the first and second output voltages.
6. A method of generating an output voltage, the method comprising:
varying resistance of a resistor in response to a first control voltage to establish a first voltage;
varying a current flowing through a current sink in response to a second control voltage to establish a second voltage; and
switching a voltage across an external load from the first voltage to the second voltage in response to a first set of input voltages and switching the voltage across the external load from the second voltage to the first voltage in response to a second set of input voltages, wherein the resistance of the resistor is controlled by a first operational amplifier and the current flow through the current sink is controlled by a second operational amplifier, wherein the first and second operational amplifiers are disposed in a control circuit further comprising:
a voltage-controlled resistor having a resistance that is adapted to vary in response to the output voltage of the first operational amplifier; and
a voltage-controlled current sink configured to sink a current that is adapted to vary in response to the output voltage of the second operational amplifier wherein the current flowing through the current sink is L times the current flowing through the voltage-controlled current sink, wherein L is a variable greater than or equal to one.