AMPLIFIER CIRCUIT AND OPTICAL PICKUP DEVICE

Abstract

An amplifier circuit according to the present invention includes: a first operational amplifier having a negative input terminal, a positive input terminal, and an output terminal; a photodiode connected to the negative input terminal; a first resistor inserted between the output terminal and the negative input terminal; and a second resistor inserted between the output terminal and the positive input terminal, in which the amplifier circuit outputs current from the output terminal via the second resistor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the invention. In the Drawings:

FIG. 1 is a diagram showing an amplifier circuit according to the conventional technology;

FIG. 2 is a diagram showing gain-frequency characteristic of the amplifier circuit according to the conventional technology;

FIG. 3 is a diagram showing an amplifier circuit according to the first embodiment;

FIG. 4 is a detailed circuit diagram of the amplifier circuit;

FIG. 5 is a diagram showing gain-frequency characteristic of an amplifier circuit;

FIG. 6 is a diagram showing an amplifier circuit according to the second embodiment;

FIG. 7A is a diagram showing an amplifier circuit according to the third embodiment;

FIG. 7B is a diagram showing a detailed structure of a buffer circuit;

FIG. 8 is a diagram showing an amplifier circuit according to the fourth embodiment;

FIG. 9 is a diagram showing an amplifier circuit according to the fifth embodiment;

FIG. 10 is a diagram showing a detailed structure of an operational amplifier;

FIG. 11 is a diagram showing an amplifier circuit according to the sixth embodiment;

FIG. 12 is a diagram showing an amplifier circuit according to the sixth embodiment;

FIG. 13 is a diagram showing an amplifier circuit according to the eighth embodiment;

FIG. 14 is a diagram showing an amplifier circuit according to the ninth embodiment;

FIG. 15 is a diagram showing an amplifier circuit according to the tenth embodiment; and

FIG. 16 is a diagram showing an amplifier circuit according to the eleventh embodiment.

Claims

1. An amplifier circuit comprising: a first operational amplifier including a negative input terminal, a positive input terminal, and an output terminal;a photodiode connected to the negative input terminal;a first resistor inserted between the output terminal and the negative input terminal; anda second resistor inserted between the output terminal and the positive input terminal,wherein said amplifier circuit outputs current from the output terminal via said second resistor.

2. The amplifier circuit according to claim 1, further comprising a second operational amplifier and a third resistor,wherein the positive input terminal of said first operational amplifier and an input terminal of said second operational amplifier are connected, andthe third resistor is inserted between the input terminal of said second operational amplifier and an output terminal of said second operational amplifier.

3. The amplifier circuit according to claim 1, further comprising a current buffer circuit to which the current outputted from the output terminal of said first operational amplifier via said second resistor is inputted.

4. The amplifier circuit according to claim 3, wherein said current buffer circuit has a function for amplifying current.

5. The amplifier circuit according to claim 3, wherein said current buffer circuit includes a bias circuit, which is for setting a bias voltage to an output signal line for outputting current from the output terminal of said first operational amplifier via said second resistor.

6. The amplifier circuit according to claim 1, wherein said first resistor includes: plural resistance elements; and a first switch circuit which selectively switches one of the resistance elements to be inserted between the output terminal of said first operational amplifier and the negative input terminal of said first operational amplifier.

7. The amplifier circuit according to claim 6, wherein said first amplifier circuit further includes plural capacitive elements for phase compensation, andthe first switch circuit switches one of the capacitive elements in conjunction with the switching of the resistance elements.

8. The amplifier circuit according to claim 1, wherein said second resistor includes plural resistance elements and a second switch circuit which selectively switches one of the resistance elements to be inserted between the output terminal of said first operational amplifier and the positive input terminal of said first operational amplifier.

9. The amplifier circuit according to claim 1, further comprising an output voltage control circuit which prevents a voltage of the output terminal of said first operational amplifier from exceeding a predetermined voltage.

10. The amplifier circuit according to claim 1, further comprising a base current compensation circuit which is connected to the negative input terminal of said first operational amplifier and the positive input terminal of said first operational amplifier, and compensates base current of input transistors in said first operational amplifier, the input transistors respectively being connected to the negative input terminal of said first operational amplifier and the positive input terminal of said first operational amplifier.

11. An amplifier circuit comprising: a first operational amplifier including a negative input terminal, a positive input terminal, and an output terminal;a photodiode which receives laser light reflected on an optical disc, and is connected to the negative input terminal;a first resistor inserted between the output terminal and the negative input terminal; anda second resistor inserted between the output terminal and the positive input terminal,wherein the amplifier circuit outputs current from the output terminal via said second resistor.

12. An optical pickup device comprising an amplifier circuit, wherein said amplifier circuit includes:a first operational amplifier having a negative input terminal, a positive input terminal, and an output terminal;a photodiode connected to the negative input terminal;a first resistor inserted between the output terminal and the negative input terminal; anda second resistor inserted between the output terminal and the positive input terminal,wherein said amplifier circuit outputs current from the output terminal via said second resistor.