JP3208791B2 - CCD image sensor and driving method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CCD image sensor such as a CCD linear sensor and a driving method thereof .

[0002]

2. Description of the Related Art In a CCD linear sensor, signal charges of odd-numbered light receiving elements (pixels) and even-numbered light receiving elements (pixels) are divided and transferred to two charge transfer registers in accordance with the increase in resolution. Then, at the final stage, the output is collectively output as one. That is, as shown in FIG. 4, a plurality of light receiving elements (pixels) S [S ₁ , S ₂ , S ₃ ...] Are arranged on both sides of a light receiving region 1 arranged in one direction via readout gates 2 and 3, respectively. First and second horizontal transfer registers 4 and 5 having a CCD structure are arranged, and signal charges of odd-numbered light receiving elements S ₁ , S ₃ , S ₅ ... Are read out to the first horizontal transfer register 4, Even-numbered light receiving elements S ₂ , S ₄ ,
The signal charges of S ₆ ... Are read out to the second horizontal transfer register 5, and each signal charge is generated by the two-phase driving pulses ΦH ₁ , ΦH ₂ and ΦH ₁ ′, ΦH ₂ ′ shown in FIGS. 5A and 5B, respectively. Is transferred in one direction. The transfer units HR ₁ and HR ₂ at the final stage have the transfer units H
Drive pulses ΦH ₁ ′ and ΦH ₁ ′, which are synchronized with the drive pulses ΦH ₁ and ΦH ₂ given to R ₁ and HR ₂ , respectively.
H ₂ 'is applied. The transfer units HR ₁ and HR _{2 at the} final stage of each of the first and second horizontal transfer registers 4 and 5 are connected to a common floating diffusion region via a common horizontal output gate unit 6 to which a gate voltage V _HOG is applied. 7, the odd-numbered and even-numbered signal charges transferred by the first and second horizontal transfer registers 4 and 5 are added to one in the floating diffusion region 7, that is, the odd-numbered and even-numbered signal charges are added. The signal charges are alternately transferred to the floating diffusion region 7, charge-to-voltage converted, and the signals corresponding to the odd and even pixels are sequentially alternated through the output amplifier 8 as shown by the CCD output waveform shown in FIG. Is output. At this output portion, the signal charges transferred to the floating diffusion region 7 are sequentially reset by a reset gate portion 9 by a reset pulse ΦRG having a frequency twice as high as the drive pulses ΦH ₁ , ΦH ₂ and ΦH ₁ ′, ΦH ₂ ′ shown in FIG. 5C. Through the reset drain region 10.

[0003]

The above-mentioned C
In the CD linear sensor, since the large capacitance of the first transfer unit HR ₁ and the second transfer unit HR ₂ in the horizontal transfer registers 4 and 5 are driven by the drive pulses ΦH ₁ and ΦH ₂ , a noise component caused by the capacitance is used. Is superimposed on the output signal, for example, the signal period becomes non-uniform, the signal level of the odd-numbered pixel (light-receiving element) and the signal of the even-numbered pixel (light-receiving element) when readout by the two horizontal transfer registers 4 and 5 A level difference (a so-called DC step) occurs.

That is, in the output section, the float is placed in the well area.
Forming region 7 is formed, and the well region is
Although it is grounded through the wiring, the transfer unit HR₁, HR_Two
The horizontal transfer registers 4 and 5 have two phases because of the large capacity of
Drive pulse ΦH₁And ΦH _TwoWhen driving with
As shown, the signal charge is transferred to the floating diffusion region.
Drive pulse ΦH to be transferred into region 7₁Or ΦH_TwoFalling
Time t₁, T_Two, T_Three…… instantaneously the potential of the well region
(So-called reference potential) V₀Fluctuates, and this fluctuation component 15
Noise component 16 is superimposed on the output signal based on
become. Therefore, the signal period is determined by the noise component 16.
Waveform is not flat. Also, the first transfer unit HR₁of
Capacity and second transfer unit HR_TwoDue to the difference in capacity
Noise component 16 is different, and as a result, the signal of the odd-numbered pixel is
Signal level and the signal level of the even-numbered pixel (so-called DC
Step). And the CCD linear sensor
As the signal level difference becomes conspicuous with higher resolution,
It is necessary to perform correction for each element, which is inconvenient.

In view of the above, the present invention provides a CCD image sensor capable of flattening a waveform in a signal period and improving a signal level difference between pixels, and a driving method thereof .

[0006]

A CCD image pickup device according to the present invention detects a plurality of charge transfer registers 4 and 5 and signal charges transferred from the plurality of charge transfer registers 4 and 5 alternately as an output signal. CCD having a common detection unit 7 and a reset gate unit 9 to which a reset pulse ΦRG for sweeping out signal charges detected by the detection unit 7 is applied.
In the imaging device, the transfer unit 12 at the last stage of the plurality of charge transfer registers 4 and 5 is separated, and the falling points of the drive pulses ΦH ₁ and ΦH ₂ applied to the transfer unit 13 before the last stage are reset. The configuration is such that the noise component 16 is superimposed on the output waveform during the ON period of the reset gate unit 9 so that the pulse ΦRG is in the high level period. The driving method of the CCD image pickup device according to the present invention includes a plurality of charge transfer registers 4 and 5, and a common detection unit 7 for alternately detecting signal charges transferred from the plurality of charge transfer registers 4 and 5 as output signals. And a method for driving a CCD image pickup device having a reset gate section 9 to which a reset pulse ΦRG for sweeping out signal charges detected by the detection section 7 is applied.
Separate drive pulses ΦH ₁ , ΦH _{2 with} phase shifts are applied to the final stage of the charge transfer register and the transfer unit before this final stage.
And the reset pulse ΦRG is set at the falling point of the drive pulses ΦH ₁ and ΦH ₂ applied to the transfer section before the final stage.
High-level period. Then, a noise component is superimposed on the output waveform during the ON period of the reset gate unit.

[0007]

In the present invention, the charge transfer registers 4 and 5
Is separated from the transfer unit 12 in the last stage, and the transfer unit 1 in the last stage is separated.
Driving pulses .PHI.H ₁ to be applied to the 2 ', .PHI.H _2' and the drive pulse .PHI.H ₁ to be applied to the front of the transfer unit 13 from the final stage portion, [Phi
The noise component 16 is superimposed on the output waveform of the reset gate unit 9 during the ON period by shifting the phase of H _{2 so that} the falling points of the drive pulses ΦH ₁ and ΦH ₂ fall in the high level period of the reset pulse ΦRG. Accordingly, the noise component 16 is not superimposed on the waveform of the signal period after the end of the ON period of the reset gate unit 9, that is, the output signal. Therefore, the output waveform in the signal period becomes flat, and the signal level difference between pixels is improved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS.
A case where the CD image pickup device and the driving method thereof are applied to a CCD linear sensor will be described.

In FIG. 1, reference numeral 1 denotes a plurality of light receiving elements S [S
_1, S _2, S ₃ ......] a shows the light receiving region formed by arranging a row in one direction, each readout gate portion 2 and 3 on both sides
Of the CCD structure so as to be parallel to the light receiving area 1 through the
The horizontal transfer register 4 and the second horizontal transfer register 5 are arranged. The first and second horizontal transfer registers 4 and 5 have a plurality of transfer units HR [HR ₁ , HR] each having a transfer electrode, which is a set of a storage electrode and a transfer electrode (not shown).
₂ ] are arranged, one drive pulse ΦH ₁ of the two-phase drive pulse is applied to the transfer electrodes of _every other first transfer unit HR ₁ , and the transfer electrodes of every other second transfer unit HR ₂ Is applied with the other drive pulse ΦH ₂ . The first transfer section HR ₁ of the first horizontal transfer register 4 is formed corresponding to, for example, the odd-numbered light receiving elements S ₁ , S ₃ , S ₅ ,. the first transfer section HR _1, for example the even-numbered light receiving element S _2, S _4, S _6, and is formed corresponding to .... First and second horizontal transfer registers 4
, And 5 are connected to a common detection unit, that is, a floating diffusion region 7 via a common horizontal output gate unit 6 to which a gate voltage V _HOG is applied. An output amplifier 8 is connected to the floating diffusion region 7. Connected. A reset gate portion 9 to which a reset pulse ΦRG is applied is formed between the floating diffusion region 7 and the reset drain region 10.

In this CCD linear sensor, the signal charges of the odd-numbered light receiving elements S ₁ , S ₃ , S ₅ ,... Are read out to the first horizontal transfer register 4 in the same manner as described above, and the even-numbered light receiving elements are read out. After the signal charges of the elements S ₂ , S ₄ , S ₆ ... Are read out to the second horizontal transfer register 5 and transferred to one of the first and second horizontal transfer registers, the horizontal output gate section 6 Through the floating diffusion region through 1
That is, the odd-numbered signal charges and the even-numbered signal charges are alternately transferred to the floating diffusion region 7. Then, charge-voltage conversion is performed in the floating diffusion region 7, and signals corresponding to odd-numbered and even-numbered pixels are output alternately through the output amplifier 8.

However, in the present embodiment, the first and second
The transfer section at the end of the horizontal transfer register
Or the transfer area 12 for a plurality of bits including the last bit.
And the first transfer unit H in the transfer area 12 in the final portion.
R₁Drive pulse ΦH₁'(See FIG. 2A)
Department HR_TwoDrive pulse ΦH_Two'(See FIG. 2A)
In addition, from the last stage of the first and second horizontal transfer registers,
The first transfer unit HR of the previous transfer area 13₁Drive pulse Φ
H₁(Refer to FIG. 2B) to the second transfer unit HR_TwoDrive pulse
ΦH_Two(Refer to FIG. 2B). Lycee
The drive gate ΦH is applied to the₁, Φ
H₁', ΦH_Two, ΦH_Two′ Reset frequency
Lus ΦRG is applied. And large transfer area
In driving the region 13, the signal charges are transferred to the transfer section HR in the next stage.
Drive pulse ΦH to send₁Or ΦH _TwoFall time t₁,
t_Two, ...... within the high level period of the reset pulse ΦRG
Correspondingly, the drive applied to the transfer area 12 at the last stage is
Dynamic pulse ΦH₁', ΦH_Two′
Drive pulse ΦH applied to the transmission region 13₁, ΦH_TwoPhase of
Are shifted by Δt.

According to such a configuration, the drive pulse applied thereto from the previous transfer area 13 driving pulses .PHI.H ₁ to be applied to the transfer area 12 of the final stage partial ', .PHI.H _2' against .PHI.H
_1, out of phase with .PHI.H ₂ only Delta] t, coming in the drive pulse .PHI.H ₁ to transfer the next stage to the signal charges, the high level period of the falling time of .PHI.H ₂ reset pulse .phi.RG (on-period of the so-called reset gate portion) by way, noise component 16 based on the fluctuation component 15 (see FIG. 2E) of the reference potential V ₀ well region is superimposed on the output waveform of the oN period T _R of the reset gate portion 9 as shown in FIG. 2D The output waveform in the signal period T _S is not superimposed on the so-called signal waveform. Therefore, the output waveform in the signal period T _S can be flattened. Also, it is possible to eliminate the difference between the signal level of the odd-numbered pixel and the signal level of the even-numbered pixel,
High-resolution image quality can be obtained without correcting the black signal of each pixel.

Next, the above-described driving pulses ΦH ₁ ', ΦH
_A specific example of shifting the phases of ₂ ′ and the drive pulses ΦH ₁ and ΦH ₂ will be described. For example, CCD with on-chip timing system
In the case of the linear sensor, as shown in FIG. 3, the clock pulses ΦH ₁ ′ and ΦH ₂ ′ for the final stage and the reset pulse ΦRG obtained by the timing generator 21 are supplied to the drive circuit 22 as they are, and the terminal a ₁ ~a _n connected to the delay circuit 23 is provided, the clock pulses .PHI.H ₁ from the timing generator 21 to the delay circuit 23 ', .PHI.H _2' supplies Δt only clock pulses .PHI.H ₁ with shifted phase , ΦH ₂ , and supplies them to the drive circuit 24. Since vary the frequency using the delay amount Δt of the delay circuit 23, by switching the voltage of the external control terminal a ₁ ~a _n digitally, it is possible to change. By shifting the phases of the drive pulses ΦH ₁ ′ and ΦH ₂ ′ and the drive pulses ΦH ₁ and ΦH ₂ in this manner, the effect of the transfer capacity in the transfer area 13 in the CCD linear sensor is reduced, and the output waveform during the signal period is reduced. Can be made flat, and the signal level difference between pixels can be improved.

In the above example, the signal charges of the first horizontal transfer register 4 and the second horizontal transfer register 5 are alternately transferred to the floating diffusion region 7 and combined into one. A two-phase drive transfer unit for several bits is provided at a stage preceding the floating diffusion region 7, and the signal charges from the first and second horizontal transfer registers 4 and 5 are alternately transferred to the transfer unit for several bits. Here, it can be configured to be integrated into one. In this case, the first and second horizontal transfer registers 4 and 5 before adding the odd-numbered and even-numbered signal charges in the transfer unit are used.
The transfer region 12 for a plurality of bits at the last stage is separated from the transfer region 13 before that, and drive pulses ΦH ₁ ′, ΦH ₂ ′, ΦH ₁ , and ΦH ₂ are applied with the above phase relationship.

In the above example, the present invention is applied to a CCD linear sensor having first and second horizontal transfer registers 4 and 5. However, the present invention is not limited to this. CCD read by horizontal transfer register
The present invention can also be applied to an area image sensor.

[0016]

According to the CCD image pickup device of the present invention, the output waveform in the signal period is flattened, and the level difference between the pixels, for example, the signal level corresponding to the odd-numbered pixel and the signal level corresponding to the even-numbered pixel is obtained. Can be improved, and high-resolution image quality can be obtained without correcting the black signal.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a CCD linear sensor according to the present invention.

FIG. 2 is a waveform diagram of a supply pulse, a CCD output waveform, and the like according to the present invention.

FIG. 3 is a circuit diagram for obtaining a supply pulse according to the present invention.

FIG. 4 is a configuration diagram of a conventional CCD linear sensor.

FIG. 5 is a waveform diagram of a supply pulse, a CCD output waveform, and the like according to a conventional example.

[Explanation of symbols]

S _{1 to} S ₁₆ light receiving element 1 light receiving area 2, 3 readout gate section 4, 5 horizontal transfer register 6 horizontal output gate section 7 floating diffusion area 8 output amplifier 9 reset gate section 10 reset drain area ΦH ₁ , ΦH ₁ ′, ΦH ₂ , ΦH ₂ ′ drive pulse ΦRG reset pulse 15 fluctuation component 16 noise component

Claims (3)

(57) [Claims] 1. A plurality of charge transfer registers, a common detection unit that alternately detects signal charges transferred from the plurality of charge transfer registers as an output signal, and sweeps out signal charges detected by the detection unit. Reset pulse is applied
In the CCD image pickup device having a reset gate section, a transfer section at a last stage of the plurality of charge transfer registers is separated, and a driving pulse applied to a transfer section before the last stage is separated .
The falling point is the high level period of the reset pulse.
CCD imaging device, characterized in that to superimpose the noise component in the output waveform of the ON period of the reset gate portion as. A plurality of charge transfer registers; a plurality of charge transfer registers;
The signal charge transferred from the load transfer register is output
And a common detection unit for detecting the
Reset pulse is applied to sweep out the
For driving CCD imaging device having reset gate section
In the the transfer unit before the final stage portion and said end-stage portion of the charge transfer register, applying a separate driving pulse out of phase, before
Fall of the drive pulse applied to the transfer section before the last stage
At a high level period of the reset pulse.
A method for driving a CCD imaging device, characterized in that: 3. The driving method for a CCD image pickup device according to claim 2, wherein a noise component is superimposed on an output waveform during an ON period of the reset gate unit.