Digitally controlled voltage generator
A digitally controlled voltage generator is disclosed for use in applications requiring fine resolution voltage control, such as generating a common voltage for a liquid crystal display. A constant resistance digital to analog converter (DAC) is configured to provide appropriate voltage steps by tuning bias resistors to generate desirable reference voltages for the DAC. The bias resistors are configured to be tuned after placement and routing steps in an integrated circuit design.
1. An LCD display device comprising:
a plurality of LCD elements to which is supplied a common voltage reference; and
a common voltage reference generator including a constant resistance digital-to-analog converter having a resistor network for generating an output voltage from which the common voltage reference is generated,
wherein the common voltage reference generator further includes a resistor divider including a first resistor and a second resistor connected in series between an analog reference voltage and ground, a third resistor connected at a first end to a node between the first resistor and the second resistor and at a second end to the constant resistance digital-to-analog convertor, and a fourth resistor connected in series between the constant resistance digital-to-analog converter and ground.
2. The LCD display device according to claim 1 , wherein the common voltage reference generator further includes an output driver for receiving the output voltage from the constant resistance digital-to-analog converter and generating the common voltage reference.
3. The LCD display device according to claim 1 , wherein the constant resistance digital-to-analog converter further includes a plurality of gates that are controlled to generate the output voltage at a desired level.
4. The LCD display device according to claim 3 , wherein the gates are controlled in accordance with a fixed-length integer value.
5. The LCD display device according to claim 3 , wherein the constant resistance digital-to-analog converter includes a resistor network.
6. The voltage generator according to claim 3 , wherein the constant resistance digital-to-analog converter includes a linear string of serially connected resistors.
7. The voltage generator according to claim 3 , wherein the constant resistance digital-to-analog converter includes a plurality of resistor segments, each having a string of serially connected resistors.
8. The LCD display device according to claim 1 , wherein the resistor network includes a linear string of serially connected resistors.
9. The LCD display device according to claim 1 , wherein the resistor network includes a plurality of resistor segments, each having a string of serially connected resistors.
10. The LCD display device according to claim 1 , wherein an electrical path between an analog reference voltage and the constant resistance digital-to-analog converter does not traverse an amplifier.
11. The LCD display device according to claim 1 , comprising a first operational amplifier having a first input coupled to an output of the constant resistance digital-to-analog converter and a first output coupled to a first electrode of a first transistor, and a second operational amplifier having a second input coupled to a second electrode of the first transistor.
12. A method comprising:
providing a plurality of LCD elements to which is supplied a common voltage reference; and
providing a common voltage reference generator including a constant resistance digital-to-analog converter having a resistor network for generating an output voltage from which the common voltage reference is generated,
wherein the common voltage reference generator further includes a resistor divider including a first resistor and a second resistor connected in series between an analog reference voltage and ground, a third resistor connected at a first end to a node between the first resistor and the second resistor and at a second end to the constant resistance digital-to-analog convertor, and a fourth resistor connected in series between the constant resistance digital-to-analog converter and ground.
13. The method according to claim 12 , wherein the common voltage reference generator further includes an output driver for receiving the output voltage from the constant resistance digital-to-analog converter and generating the common voltage reference.
14. The method according to claim 12 , wherein the constant resistance digital-to-analog converter further includes a plurality of gates that are controlled to generate the output voltage at a desired level.
15. The method according to claim 14 , wherein the gates are controlled in accordance with a fixed-length integer value.
16. The method according to claim 14 , wherein the constant resistance digital-to-analog converter includes a resistor network.
17. The method according to claim 14 , wherein the constant resistance digital-to-analog converter includes a linear string of serially connected resistors.
18. The method according to claim 14 , wherein the constant resistance digital-to-analog converter includes a plurality of resistor segments, each having a string of serially connected resistors.
19. The method according to claim 12 , wherein the resistor network includes a linear string of serially connected resistors.
20. The method according to claim 12 , wherein the resistor network includes a plurality of resistor segments, each having a string of serially connected resistors.
21. The method according to claim 12 , wherein an electrical path between an analog reference voltage and the constant resistance digital-to-analog converter does not traverse an amplifier.
22. The method according to claim 12 , further comprising:
providing a first operational amplifier having a first input coupled to an output of the constant resistance digital-to-analog converter and a first output coupled to a first electrode of a first transistor; and
providing a second operational amplifier having a second input coupled to a second electrode of the first transistor.
23. An device comprising:
a plurality of LCD elements to which is supplied a common voltage reference;
a common voltage reference generator including a constant resistance digital-to-analog converter having a resistor network for generating an output voltage from which the common voltage reference is generated,
wherein the common voltage reference generator further includes a resistor divider including a first resistor and a second resistor connected in series between an analog reference voltage and ground, a third resistor connected at a first end to a node between the first resistor and the second resistor and at a second end to the constant resistance digital-to-analog convertor, and a fourth resistor connected in series between the constant resistance digital-to-analog converter and ground; and
an output driver for receiving the output voltage from the constant resistance digital-to-analog converter and generating the common voltage reference.
24. The device according to claim 23 , wherein the output driver comprises a voltage-to-current converter circuit and a voltage driver circuit.
25. The device according to claim 23 , wherein the output driver comprises:
a first operational amplifier comprising a first input coupled the constant resistance digital-to-analog converter and a first output; and
a first transistor comprising a first electrode coupled to the first output of the first operational amplifier.
26. The device according to claim 25 , wherein the output driver comprises:
a second operational amplifier comprising a second input coupled to a second electrode of the first transistor.
27. The device according to claim 23 , wherein the resistor network includes a linear string of serially connected resistors.
28. The device according to claim 23 , wherein the resistor network includes a plurality of resistor segments, each having a string of serially connected resistors.
29. The device according to claim 23 , wherein an electrical path between an analog reference voltage and the constant resistance digital-to-analog converter does not traverse an amplifier.
30. The device according to claim 23 , wherein an electrical path between an analog reference voltage and the constant resistance digital-to-analog converter does not traverse an amplifier.