Constant voltage circuit and constant current source, amplifier, and power supply circuit using the same

• US 20060022660A1
• Filed: 07/25/2005
• Published: 02/02/2006
• Est. Priority Date: 07/28/2004
• Status: Active Grant

• Current Assignee: RICOH Electronic Devices Co., Ltd. (Nisshinbo Holdings Incorporated)
• Original Assignee: Ricoh Company Limited
• Inventors: Itoh, Kohzoh
• Granted Patent: US 7,202,655 B2
• Time in Patent Office: Days
• US Class Current: 323/312
• CPC Class Codes: G05F 1/575 characterised by the feedback circuit
• CPC Class Codes: H02M 3/07 using capacitors charged and discharged alternately by semiconductor devices with control electrode , e.g. charge pumps

Abstract

A constant voltage circuit is disclosed that includes a constant voltage generator circuit part converting an input voltage into a predetermined constant voltage in accordance with an externally input control signal and outputting the constant voltage; a first capacitor connected to the output end of the constant voltage generator circuit part; a second capacitor charging the first capacitor; and a switch circuit part controlling charging and discharging of the second capacitor in accordance with the control signal. The switch circuit part charges the second capacitor and blocks the discharging of the second capacitor to the first capacitor when the constant voltage generator circuit part is caused to stop outputting the constant voltage by the control signal, and stops applying the input voltage to the second capacitor and charges the first capacitor when the constant voltage generator circuit part is caused to start outputting the constant voltage by the control signal.

Claims

1. A constant voltage circuit converting an input voltage into a predetermined constant voltage in accordance with an externally input control signal and outputting the predetermined constant voltage, the constant voltage circuit comprising:

a constant voltage generator circuit part configured to convert the input voltage into the predetermined constant voltage in accordance with the control signal and output the predetermined constant voltage;

a first capacitor connected to an output end of the constant voltage generator circuit part outputting the constant voltage;

a second capacitor configured to charge the first capacitor; and

a switch circuit part configured to control charging and discharging of the second capacitor in accordance with the control signal,

wherein the switch circuit part charges the second capacitor by applying the input voltage thereto and blocks the discharging of the second capacitor to the first capacitor when the constant voltage generator circuit part is caused to stop outputting the predetermined constant voltage by the control signal; and

the switch circuit part stops applying the input voltage to the second capacitor and charges the first capacitor by releasing an electric charge stored in the second capacitor to the first capacitor when the constant voltage generator circuit part is caused to start outputting the predetermined constant voltage by the control signal.

2. The constant voltage circuit as claimed in claim 1, wherein the constant voltage generator circuit part releases an electric charge stored in the first capacitor when the constant voltage generator circuit part is caused to stop outputting the predetermined constant voltage by the control signal.

3. The constant voltage circuit as claimed in claim 1, wherein the switch circuit part comprises:

a first switch circuit configured to charge the second capacitor with the input voltage in accordance with the control signal; and

a second switch circuit configured to charge the first capacitor with a voltage of the second capacitor in accordance with the control signal.

4. The constant voltage circuit as claimed in claim 1, wherein the first and second capacitors remove noise superposed on the constant voltage output from the constant voltage generator circuit part.

5. The constant voltage circuit as claimed in claim 1, wherein capacitance of the first capacitor and capacitance of the second capacitor have a relationship of Vdd/V1=(C1+C2)/C2, where Vdd is the input voltage, V1 is the predetermined constant voltage, C1 is the capacitance of the first capacitor, and C2 is the capacitance of the second capacitor.

6. The constant voltage circuit as claimed in claim 1, wherein the constant voltage generator circuit part, the first capacitor, the second capacitor, and the switch circuit part are integrated into a single IC.

7. A constant current source, comprising:

a constant voltage circuit converting an input voltage into a predetermined constant voltage in accordance with an externally input control signal and outputting the predetermined constant voltage, the constant voltage circuit including;

a constant voltage generator circuit part configured to convert the input voltage into the predetermined constant voltage in accordance with the control signal and output the predetermined constant voltage;

a first capacitor connected to an output end of the constant voltage generator circuit part outputting the constant voltage;

a second capacitor configured to charge the first capacitor; and

a switch circuit part configured to control charging and discharging of the second capacitor in accordance with the control signal,

wherein the switch circuit part charges the second capacitor by applying the input voltage thereto and blocks the discharging of the second capacitor to the first capacitor when the constant voltage generator circuit part is caused to stop outputting the predetermined constant voltage by the control signal;

the switch circuit part stops applying the input voltage to the second capacitor and charges the first capacitor by releasing an electric charge stored in the second capacitor to the first capacitor when the constant voltage generator circuit part is caused to start outputting the predetermined constant voltage by the control signal; and

the constant current source generates a constant current by converting the constant voltage output from the constant voltage circuit into current, and outputs the constant current.

8. The constant current source as claimed in claim 7, wherein the constant voltage generator circuit part releases an electric charge stored in the first capacitor when the constant voltage generator circuit part is caused to stop outputting the predetermined constant voltage by the control signal.

9. The constant current source as claimed in claim 7, wherein the switch circuit part comprises:

a first switch circuit configured to charge the second capacitor with the input voltage in accordance with the control signal; and

a second switch circuit configured to charge the first capacitor with a voltage of the second capacitor in accordance with the control signal.

10. The constant current source as claimed in claim 7, wherein the first and second capacitors remove noise superposed on the constant voltage output from the constant voltage generator circuit part.

11. The constant current source as claimed in claim 7, wherein capacitance of the first capacitor and capacitance of the second capacitor have a relationship of Vdd/V1=(C1+C2)/C2, where Vdd is the input voltage, V1 is the predetermined constant voltage, C1 is the capacitance of the first capacitor, and C2 is the capacitance of the second capacitor.

12. The constant current source as claimed in claim 7, wherein the constant current source is integrated into a single IC.

13. An amplifier, comprising:

a constant current source,

the constant current source including a constant voltage circuit converting an input voltage into a predetermined constant voltage in accordance with an externally input control signal and outputting the predetermined constant voltage,

the constant voltage circuit including;

a constant voltage generator circuit part configured to convert the input voltage into the predetermined constant voltage in accordance with the control signal and output the predetermined constant voltage;

a first capacitor connected to an output end of the constant voltage generator circuit part outputting the constant voltage;

a second capacitor configured to charge the first capacitor; and

a switch circuit part configured to control charging and discharging of the second capacitor in accordance with the control signal,

wherein the switch circuit part charges the second capacitor by applying the input voltage thereto and blocks the discharging of the second capacitor to the first capacitor when the constant voltage generator circuit part is caused to stop outputting the predetermined constant voltage by the control signal;

the switch circuit part stops applying the input voltage to the second capacitor and charges the first capacitor by releasing an electric charge stored in the second capacitor to the first capacitor when the constant voltage generator circuit part is caused to start outputting the predetermined constant voltage by the control signal; and

the constant current source supplies bias current to an amplifier circuit by generating a constant current by converting the constant voltage output from the constant voltage circuit into current.

14. The amplifier as claimed in claim 13, wherein the constant voltage generator circuit part releases an electric charge stored in the first capacitor when the constant voltage generator circuit part is caused to stop outputting the predetermined constant voltage by the control signal.

15. The amplifier as claimed in claim 13, wherein the switch circuit part comprises:

a first switch circuit configured to charge the second capacitor with the input voltage in accordance with the control signal; and

a second switch circuit configured to charge the first capacitor with a voltage of the second capacitor in accordance with the control signal.

16. The amplifier as claimed in claim 13, wherein the first and second capacitors remove noise superposed on the constant voltage output from the constant voltage generator circuit part.

17. The amplifier as claimed in claim 13, wherein capacitance of the first capacitor and capacitance of the second capacitor have a relationship of Vdd/V1=(C1+C2)/C2, where Vdd is the input voltage, V1 is the predetermined constant voltage, C1 is the capacitance of the first capacitor, and C2 is the capacitance of the second capacitor.

18. The amplifier as claimed in claim 13, wherein:

the amplifier circuit is a differential amplifier circuit having a differential pair; and

the constant current source supplies the bias current to the differential pair.

19. The amplifier as claimed in claim 13, wherein the amplifier is integrated into a single IC.

20. A power supply circuit, comprising:

an amplifier,

the amplifier including a constant current source, the constant current source including a constant voltage circuit converting an input voltage into a predetermined constant voltage in accordance with an externally input control signal and outputting the predetermined constant voltage,

the constant voltage circuit including;

a constant voltage generator circuit part configured to convert the input voltage into the predetermined constant voltage in accordance with the control signal and output the predetermined constant voltage;

a first capacitor connected to an output end of the constant voltage generator circuit part outputting the constant voltage;

a second capacitor configured to charge the first capacitor; and

a switch circuit part configured to control charging and discharging of the second capacitor in accordance with the control signal,

wherein the switch circuit part charges the second capacitor by applying the input voltage thereto and blocks the discharging of the second capacitor to the first capacitor when the constant voltage generator circuit part is caused to stop outputting the predetermined constant voltage by the control signal;

the switch circuit part stops applying the input voltage to the second capacitor and charges the first capacitor by releasing an electric charge stored in the second capacitor to the first capacitor when the constant voltage generator circuit part is caused to start outputting the predetermined constant voltage by the control signal;

the constant current source supplies bias current to an amplifier circuit by generating a constant current by converting the constant voltage output from the constant voltage circuit into current;

the amplifier controls an operation of a transistor connected to an input terminal and an output terminal so that a voltage at the output terminal is a predetermined voltage; and

the power supply circuit converts the voltage input to the input terminal into a predetermined voltage and outputs the predetermined voltage from the output terminal.

21. The power supply circuit as claimed in claim 20, wherein the constant voltage generator circuit part releases an electric charge stored in the first capacitor when the constant voltage generator circuit part is caused to stop outputting the predetermined constant voltage by the control signal.

22. The power supply circuit as claimed in claim 20, wherein the switch circuit part comprises:

a first switch circuit configured to charge the second capacitor with the input voltage in accordance with the control signal; and

a second switch circuit configured to charge the first capacitor with a voltage of the second capacitor in accordance with the control signal.

23. The power supply circuit as claimed in claim 20, wherein the first and second capacitors remove noise superposed on the constant voltage output from the constant voltage generator circuit part.

24. The power supply circuit as claimed in claim 20, wherein capacitance of the first capacitor and capacitance of the second capacitor have a relationship of Vdd/V1=(C1+C2)/C2, where Vdd is the input voltage, V1 is the predetermined constant voltage, C1 is the capacitance of the first capacitor, and C2 is the capacitance of the second capacitor.

25. The power supply circuit as claimed in claim 20, wherein:

the amplifier circuit is a differential amplifier circuit having a differential pair; and

the constant current source supplies the bias current to the differential pair.