Smoothing circuit

• US 20040032238A1
• Filed: 06/11/2003
• Published: 02/19/2004
• Est. Priority Date: 12/21/2000
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Niigata Seimitsu Co., Ltd. (Tetsuo Funai)
• Inventors: Miyagi, Hiroshi
• Granted Patent: US 6,919,710 B2
• Time in Patent Office: Days
• US Class Current: 320/166
• CPC Class Codes: H03G 3/30 in amplifiers having semiconductor devices

Abstract

A smoothing circuit for realizing the miniaturization and the increase of integration scale of a circuit and for easily varying attack time and release time. This smoothing circuit comprises a capacitor, voltage comparator, charging circuit, and discharging circuit. The voltage comparator compares the terminal voltage of the capacitor with its input voltage and actuates the charging circuit or the discharging circuit according to a comparison result. The charging circuit charges the capacitor by intermittently supplying charging current. The discharging circuit discharges the capacitor by allowing discharging current to flow intermittently.

Claims

1. A smoothing circuit comprising:

a capacitor;

a voltage comparator which compares a terminal voltage of said capacitor and an input voltage;

a charging circuit which intermittently charges said capacitor when said input voltage is higher relatively than said terminal voltage; and

a discharging circuit which intermittently releases a discharging current from said capacitor when said terminal voltage is lower relatively than said input voltage.

2. The smoothing circuit according to claim 1 wherein said charging circuit comprises a current supply section which supplies a predetermined charging current to said capacitor, and a first timing control section which controls the timing of the operation to intermittently supply the charging current by said current supply section.

3. The smoothing circuit according to claim 2 wherein said first timing control section has a switch for performing said timing control on the basis of a pulse signal having a predetermined duty ratio.

4. The smoothing circuit according to claim 3 wherein the frequency of said pulse signal is higher than twice the frequency of the input signal.

5. The smoothing circuit according to claim 2 wherein said current supply section comprises a constant-current circuit and a current mirror circuit which supplies said capacitor with the charging current equal to the current generated by said constant-current circuit.

6. The smoothing circuit according to claim 1 wherein said discharging circuit comprises a current release section which releases the predetermined discharging current from said capacitor, and a second timing control section which controls the timing of the operation to intermittently release the discharging current by said current release section.

7. The smoothing circuit according to claim 6 wherein said second timing control section has a switch for performing said timing control on the basis of a pulse signal having a predetermined duty ratio.

8. The smoothing circuit according to claim 7 wherein the frequency of said pulse signal is higher than twice the frequency of the input signal.

9. The smoothing circuit according to claim 6 wherein said current release section comprises a constant-current circuit and a current mirror circuit which releases from said capacitor the discharging current equal to the current generated by said constant-current circuit.

10. The smoothing circuit according to claim 1 wherein said charging circuit comprises a current supply section which supplies a predetermined charging current to said capacitor, and a first timing control section which controls the timing of the operation to intermittently supply the charging current by said current supply section;

said discharging circuit comprises a current release section which releases the predetermined discharging current from said capacitor, and a second timing control section which controls the timing of the operation to intermittently release the discharging current by said current release section; and

the timing of supply of the charging current controlled by said first timing control section and the timing of discharging by the discharging current controlled by said second timing control section do not overlap each other.

11. The smoothing circuit according to claim 1, further comprising charging/discharging speed setting unit for setting the speed of charging by said charging circuit and the speed of discharging by said discharging circuit to different values.

12. The smoothing circuit according to claim 11 wherein said charging circuit comprises a current supply section which supplies a predetermined charging current to said capacitor, and a first timing control section which controls the timing of the operation to intermittently supply the charging current by said current supply section;

said discharging circuit comprises a current release section which releases the predetermined discharging current from said capacitor, and a second timing control section which controls the timing of the operation to intermittently release the discharging current by said current release section; and

said charging/discharging speed setting unit sets different lengths of time as the time period for intermittent supply of the charging current controll d by said first timing control section and the time period for intermittent release of the discharging current controlled by said second timing control section.

13. The smoothing circuit according to claim 12, wherein said first and second timing control sections each have a switch for performing said timing control on the basis of a pulse signal having a predetermined duty ratio;

and

wherein said charging/discharging speed setting unit sets the duty ratio of said pulse signal for charging and the duty ratio of said pulse signal for discharging to different values.

14. The smoothing circuit according to claim 12, wherein said charging/discharging speed setting unit sets the charging current supplied by said current supply section and the discharging current released by said current release section to different values.

15. The smoothing circuit according to claim 14, wherein each of said current supply section and said current release section is constituted by a transistor having a predetermined reference voltage applied to its gate;

and

said charging/discharging speed setting unit makes the gate size of said transistor for charging and the gate size of said transistor for discharging different from each other.

16. The smoothing circuit according to claim 13 wherein the frequency of said pulse signal is higher than twice the frequency of the input signal.