Power supply generating circuit, display apparatus, and portable terminal device

• US 7,129,939 B2
• Filed: 11/15/2002
• Issued: 10/31/2006
• Est. Priority Date: 11/30/2001
• Status: Expired due to Term

• Current Assignee: Japan Display West Incorporated (Japan Display Incorporated)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Nakajima, Yoshiharu, Toyozawa, Noboru
• Primary Examiner(s): CHANG, KENT WU
• Application Number:
  US10/467,388
• Publication Number:
  US 20040055963A1
• Time in Patent Office: 1,446 Days
• Field of Search: 323/266, 345211-213, 327/536, 327142-144
• US Class Current: 345/211
• CPC Class Codes: G09G 2330/022 in absence of operation, e.g. no data being entered during a predetermined time
• CPC Class Codes: G09G 3/36 using liquid crystals
• CPC Class Codes: H02M 3/07 using capacitors charged and discharged alternately by semiconductor devices with control electrode , e.g. charge pumps
• CPC Class Codes: H02M 3/073 Charge pumps of the Schenkel-type

Abstract

A power supply generating circuit, a display apparatus incorporating the same, and a portable terminal device using the display apparatus as an output display unit are provided. In a DC-DC converter having a charge pump circuit (31), a voltage dividing circuit (32), and a regulation circuit (33), p-channel MOS transistors (Qp21, Qp22, Qp31) are turned on/off based on an enable pulse enb to make the voltage dividing circuit (32) and a comparator (41) active only for a period of regulation time and inactive otherwise. This can cause a current to flow in voltage-divider resistors (R1, R2) and the comparator (41) only for a certain period of time required for the regulation operation, thus reducing the power consumption loss caused by a constant current flow in the voltage-divider resistors (R1, R2) and the comparator (41).

Claims

1. A power supply generating circuit comprising:

charge pump means for repeating charging and discharging operations in synchronization with a clock pulse;

voltage dividing means for dividing an output voltage of the charge pump means;

regulation means, having a comparator for comparing the divided voltage obtained from the voltage dividing means with a reference voltage, for controlling the supply of the clock pulse to the charge pump means based on the comparison result of the comparator; and

control means for making at least one of the voltage dividing means and the comparator active only for a certain period of time.

2. A power supply generating circuit according to claim 1, wherein the control means makes the voltage dividing means and the comparator inactive for a period other than the period when the voltages are compared by the comparator.

3. A power supply generating circuit according to claim 1, wherein the voltage dividing means includes voltage-divider resistors connected in series between an output terminal of the charge pump means and a reference potential point, and

the control means includes switching means connected in series with the voltage-divider resistors.

4. A power supply generating circuit according to claim 1, wherein the control means includes switching means connected between a voltage-divider point of the voltage dividing circuit and an input terminal of the comparator.

5. A power supply generating circuit according to claim 1, wherein the regulation means includes holding means for holding the comparison result of the comparator.

6. A power supply generating circuit according to claim 5, wherein the regulation means applies a logical AND of a clock which transitions at a time other than a sampling time of the holding means and a hold output of the holding means to the charge pump means.

7. A power supply generating circuit according to claim 5, wherein the holding means comprises a sample-and-hold circuit or a latch circuit for sampling the comparison result of the comparator for a period for which at least one of the voltage dividing means and the comparator is active and for holding or latching it for a period other than that period, and

the comparator has an offset cancellation function and detects an offset for a certain period of time during the hold or latch period of the sample-and-hold circuit or latch circuit.

8. A display apparatus comprising a pixel unit having an array of pixels on a substrate, and power supply generating means formed on the same substrate as the pixel unit for, based on an internal circuit power supply voltage, generating a power supply voltage having a different voltage value from the internal circuit power supply voltage,

wherein the power supply generating means includes:

charge pump means for repeating charging and discharging operations in synchronization with a clock pulse;

voltage dividing means for dividing an output voltage of the charge pump means;

regulation means, having a comparator for comparing the divided voltage obtained from the voltage dividing means with a reference voltage, for controlling the supply of the clock pulse to the charge pump means based on the comparison result of the comparator; and

control means for making at least one of the voltage dividing means and the comparator active only for a certain period of time during one horizontal scanning period.

9. A display apparatus according to claim 8, wherein the control means makes the voltage dividing means and the comparator inactive for a period other than the period when the voltages are compared by the comparator.

10. A display apparatus according to claim 8, wherein the voltage dividing means includes voltage-divider resistors connected in series between an output terminal of the charge pump means and a reference potential point, and

the control means includes switching means connected in series with the voltage-divider resistors.

11. A display apparatus according to claim 8, wherein the control means includes switching means connected between a voltage-divider point of the voltage dividing circuit and an input terminal of the comparator.

12. A display apparatus according to claim 8, wherein the regulation means includes holding means for holding the comparison result of the comparator.

13. A display apparatus according to claim 12, wherein the regulation means applies a logical AND of a clock which transitions at a time other than a sampling time of the holding means and a hold output of the holding means to the charge pump means.

14. A display apparatus according to claim 12, wherein the holding means comprises a sample-and-hold circuit or a latch circuit for sampling the comparison result of the comparator for a period for which at least one of the voltage dividing means and the comparator is active and for holding or latching it for a period other than that period, and

the comparator has an offset cancellation function and detects an offset for a certain period of time during the hold or latch period of the sample-and-hold circuit or latch circuit.

15. A display apparatus according to claim 8, wherein display devices of the pixels comprise liquid crystal cells.

16. A portable terminal device which uses a display apparatus as an output display unit, the display apparatus comprising a pixel unit having an array of pixels on a substrate, and power supply generating means formed on the same substrate as the pixel unit for, based on an internal circuit power supply voltage, generating a power supply voltage having a different voltage value from the internal circuit power supply voltage,

wherein the power supply generating means includes:

charge pump means for repeating charging and discharging operations in synchronization with a clock pulse;

voltage dividing means for dividing an output voltage of the charge pump means;

regulation means, having a comparator for comparing the divided voltage obtained from the voltage dividing means with a reference voltage, for controlling the supply of the clock pulse to the charge pump means based on the comparison result of the comparator; and

control means for making at least one of the voltage dividing means and the comparator active only for a certain period of time during one horizontal scanning period.

17. A portable terminal device according to claim 16, wherein the control means makes the voltage dividing means and the comparator inactive for a period other than the period when the voltages are compared by the comparator.

18. A portable terminal device according to claim 16, wherein the voltage dividing means includes voltage-divider resistors connected in series between an output terminal of the charge pump means and a reference potential point, and

the control means includes switching means connected in series with the voltage-divider resistors.

19. A portable terminal device according to claim 16, wherein the control means includes switching means connected between a voltage-divider point of the voltage dividing circuit and an input terminal of the comparator.

20. A portable terminal device according to claim 16, wherein the regulation means includes holding means for holding the comparison result of the comparator.

21. A portable terminal device according to claim 20, wherein the regulation means applies a logical AND of a clock which transitions at a time other than a sampling time of the holding means and a hold output of the holding means to the charge pump means.

22. A portable terminal device according to claim 20, wherein the holding means comprises a sample-and-hold circuit or a latch circuit for sampling the comparison result of the comparator for a period for which at least one of the voltage dividing means and the comparator is active and for holding or latching it for a period other than that period, and

the comparator has an offset cancellation function and detects an offset for a certain period of time during the hold or latch period of the sample-and-hold circuit or latch circuit.

23. A portable terminal device according to claim 16, wherein the display apparatus comprises a liquid crystal display apparatus which uses liquid crystal cells as display devices of the pixels.