JP2005229637A - Solid imaging apparatus and its driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To connect a transmission cable of a matched impedance directly to an output terminal by lowering an output impedance of a solid imaging element and to control a heating of the solid imaging element in spite of its low output impedance. <P>SOLUTION: The solid imaging element integrated by an amplification portion 2 consisting of an imaging portion 1 and a two-stepped source follower amplifier is provided with an output portion 3 consisting of a MOS transistor with the output impedance of 75Ω or less, and a switch 11 to electrically turn on and off between the output terminal 8 of the output portion and a ground terminal and a resistance 9 are serially connected. The transmission cable with a characteristic impedance of 75Ω or less is connected directly to the output terminal thereby, a current sending to the MOS transistor of the low output impedance of the output portion is consumed by an external resistance, and the heating of the solid imaging element is controlled because the switch is turned on only when an output signal is taken out. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a solid-state imaging device and a driving method thereof.

  In a conventional solid-state imaging device, a signal output amplifier is configured only by an amplification unit of a two-stage or three-stage source follower amplifier, and a signal is directly extracted from an output terminal of the source follower amplifier.

  However, in the conventional configuration, since the output impedance of the signal output amplifier is higher than 75Ω, when transmitting an electric signal to an external signal processing circuit, the characteristic impedance of the transmission cable is 75Ω or less. Impedance matching deteriorates and transmission loss occurs, so that there is a problem that the transmission cable cannot be directly connected to the output terminal of the signal output amplifier.

  In addition, in order to make the output impedance of the signal output amplifier 7575Ω or less, when the impedance of the MOS transistor connected to the power supply terminal among the MOS transistors at the final stage of the source follower is 75Ω or less, this transistor is grounded. Since the current flowing through the load MOS transistor connected between the terminals is increased, the load MOS transistor generates heat at 60 ° C. or more, which makes it difficult to put it into practical use.

  The present invention has been made to solve the above-described conventional problems, and a solid-state imaging device in which a transmission cable can be directly connected to an output terminal of a signal output amplifier, and heat generation of a MOS transistor can be suppressed to 50 ° C. or less, and its A driving method is provided.

  In order to solve the above-described problems, the solid-state imaging device of the present invention is characterized in that an imaging unit and an output unit are integrated so that a current flows through the output unit only when an output signal is extracted from the output unit.

  Another solid-state imaging device according to the present invention is characterized in that an imaging unit and an output unit are integrated so that a current flows through the output unit only during a video period of the imaging unit.

  It is preferable that the output unit includes an amplifying unit including a multi-stage source follower.

  It is preferable that the current flowing through the output unit is adjusted by turning on and off a switch connected to the output terminal of the output unit.

  The driving method of the solid-state imaging device according to the present invention is a driving method of a solid-state imaging device in which an imaging unit and an output unit are integrated, and a current flows through the output unit only when an output signal is extracted from the output unit. It is characterized by that.

  Another solid-state imaging device driving method of the present invention is a driving method for a solid-state imaging device in which an imaging unit and an output unit are integrated, and a current flows through the output unit only during a video period of the imaging unit. It is characterized by.

  It is preferable that the output unit includes an amplifying unit including a multi-stage source follower.

  According to the present invention, it is possible to suppress heat generation of the MOS transistor inside the solid-state imaging device by suppressing unnecessary current flowing from the drain to the source of the MOS transistor of the output unit.

  Embodiments of a solid-state imaging device, a solid-state imaging device, and a driving method thereof according to the present invention will be described with reference to the drawings.

(Embodiment 1)
A solid-state imaging device according to the first embodiment of the present invention will be described with reference to FIG.

  This structure includes an imaging unit 1, an amplification unit 2 of a two-stage source follower amplifier (amplifier) composed of four MOS transistors, and an output unit 3 composed of a MOS transistor having an output impedance of 75Ω or less. The terminal 4 is connected to the gate of the first stage MOS transistor of the two-stage source follower amplifier, the gate of the load MOS transistor of the two-stage source follower amplifier is connected to the common load gate terminal 5, and the gate of the MOS transistor of the output unit 3 Is connected to the output terminal 6 of the two-stage source follower amplifier, the drain is connected to the power supply terminal 7, and the source is connected to the output terminal 8 of the output unit 3.

  Next, the operation of the solid-state imaging device having the above configuration will be described.

  First, the electric signal of the video obtained by the imaging unit 1 is input to the gate of the first stage MOS transistor of the two-stage source follower amplifier of the amplification unit 2 through the output terminal 4 of the imaging unit 1. Next, the amplified electrical signal is input from the output terminal 6 of the two-stage source follower amplifier to the gate of the MOS transistor of the output unit 3 having a low output impedance (75Ω or less), and further from the output terminal 8 of the output unit 3 to the solid state. Output to the outside of the image sensor.

  As described above, in the solid-state imaging device according to the first embodiment of the present invention, since the output unit 3 is configured with a MOS transistor of 75Ω or less, the output impedance of the output unit 3 has a low output impedance of 75Ω or less. Can be realized. Therefore, it can be directly connected to a transmission cable having a characteristic impedance of 75Ω or less.

(Embodiment 2)
A solid-state imaging device according to the second embodiment of the present invention will be described with reference to FIG.

  In this structure, as shown in FIG. 2, a resistor 9 is further connected between the output terminal 8 of the output unit 3 and the ground in the solid-state imaging device in the first embodiment, which is opposite to the ground side of the resistor 9. The signal output terminal 10 is connected to the terminal on the side, and the resistor 9 is provided outside the solid-state imaging device.

  With this structure, a large current due to the low output impedance flowing from the drain to the source of the MOS transistor of the output section can be passed through a resistor outside the solid-state image sensor, so that heat can be generated outside, and the inside of the solid-state image sensor The heat generation of the MOS transistor can be suppressed.

(Embodiment 3)
A solid-state imaging device according to the third embodiment of the present invention will be described with reference to FIG.

  As shown in FIG. 3, this structure is obtained by connecting a switch 11 between the output terminal 8 of the output unit 3 and the resistor 9 in addition to the structure of the second embodiment shown in FIG. .

  With this structure, the switch 11 is turned on only when a signal is output from the signal output terminal 10 using the switch 11, so that the MOS transistor of the output unit is turned on only at that time, and the signal is output from the signal output terminal 10. If not, the switch 11 is turned off, so that the heat generation of the MOS transistor inside the solid-state imaging device can be further suppressed.

(Embodiment 4)
A fourth embodiment of the solid-state imaging device of the present invention will be described with reference to FIG.

  In this structure, a transmission cable 12 is connected between the output terminal 8 of the output unit 3 and the resistor 9 in the structure of the second embodiment shown in FIG.

  According to this structure, the electrical signal output from the output terminal 8 of the output unit 3 is, for example, when the output impedance of the output unit 3 is 43Ω and the transmission cable 12 having a characteristic impedance of 43Ω is used. It is transmitted without causing attenuation or reflection, and a signal can be taken out from the signal output terminal 10 without loss.

  In addition, since a large current due to the low output impedance flowing from the drain to the source of the MOS transistor of the output unit 3 can flow through the transmission cable 12 to the resistor 9 outside the solid-state imaging device, heat can be generated externally by an external resistor. And heat generation inside the solid-state imaging device can be suppressed.

(Embodiment 5)
A solid-state imaging device according to the fifth embodiment of the present invention will be described with reference to FIG.

  In this structure, a switch 11 that can be electrically turned on / off is provided between the transmission cable 12 and the resistor 9 in addition to the structure of the fourth embodiment shown in FIG.

  According to this structure, in addition to the effects described in the fourth embodiment, the switch 11 is turned on only during a period in which a signal is extracted from the signal output terminal 10, and the switch 11 is turned off during other periods. Unnecessary current flowing from the drain to the source of the MOS transistor of the unit 3 can be suppressed, and the heat generation of the MOS transistor inside the solid-state imaging device can be further suppressed.

  This effect will be described in more detail.

  For example, let us consider a case in which an image of a solid-state imaging device having 50,000 pixels (horizontal 225 pixels × vertical 225 pixels) is displayed on a NTSC type 260,000 pixel television screen.

  As shown in FIG. 6, when a video signal exists only in the 50,000-pixel area 14 indicated by hatching in the 260,000-pixel TV screen 13, the 50,000 pixels are only displayed during the period of the 50,000-pixel area 14 in the hatching. If the switch 11 of the solid-state imaging device is turned on and the switch 11 is turned off otherwise, the power consumption of the MOS transistor of the output unit 3 can be suppressed to 1/5.

  Next, in the case of continuous driving in which the switch 11 of the 50,000-pixel solid-state imaging device is continuously turned on, and as shown in FIG. Compare the temperature rise of the solid-state imaging device with the intermittent drive.

  As a system for measuring the temperature rise of the solid-state imaging device, the output impedance of the MOS transistor of the output unit 3 shown in FIG. 5 is set to 43Ω, the transmission cable 12 having a characteristic impedance of 43Ω is used, and the one having a resistance of 710Ω is connected. did. Further, a series circuit composed of a 43 μF capacitor and a 43Ω resistor was connected in parallel with the switch 11 and the resistor 9.

  As a result, when the room temperature was 26 ° C., the solid-state image sensor temperature in the continuous drive was 71 ° C., whereas the solid-state image sensor temperature in the intermittent drive could be suppressed to 43 ° C.

  In the above embodiment, the resistor 9 is used as the resistor 9. However, the same effect can be obtained even with a resistor using a transistor or the like.

  The solid-state imaging device according to the present invention is useful because it can suppress heat generation inside the solid-state imaging device by suppressing unnecessary current flowing through the output unit.

1 is a configuration diagram of a main part of a solid-state imaging device according to a first embodiment of the present invention. Configuration diagram of main part of solid-state imaging device according to second embodiment of the present invention Configuration diagram of main part of solid-state imaging device according to third embodiment of the present invention Main part block diagram of the solid-state imaging device in the 4th Embodiment of this invention Main part block diagram of the solid-state imaging device in the 5th Embodiment of this invention Operation explanatory diagram of the solid-state imaging device in the fifth embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image pick-up part 2 Amplification part 3 Output part 4 Output terminal of image pick-up part 5 Load gate terminal 6 Output terminal of two-stage source follower amplifier 7 Power supply terminal 8 Output terminal of output part 9 Resistance 10 Signal output terminal 11 Switch 12 Transmission cable 13 26 10,000-pixel TV screen 1450,000-pixel area

Claims (7)

An imaging unit and an output unit are integrated, and a current flows through the output unit only when an output signal is extracted from the output unit. An imaging unit and an output unit are integrated so that a current flows through the output unit only during a video period of the imaging unit. The solid-state imaging device according to claim 1, wherein the output unit includes an amplifying unit including a multistage source follower. 4. The solid-state imaging device according to claim 1, wherein a current flowing through the output unit is adjusted by turning on and off a switch connected to an output terminal of the output unit. 5. A driving method of a solid-state imaging device in which an imaging unit and an output unit are integrated, wherein a current flows through the output unit only when an output signal is extracted from the output unit. . A driving method of a solid-state imaging device in which an imaging unit and an output unit are integrated, wherein a current flows through the output unit only during a video period of the imaging unit. The method for driving a solid-state imaging device according to claim 5, wherein the output unit includes an amplifying unit including a multistage source follower.

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