JPS59108491A - Image pickup device - Google Patents

Abstract

PURPOSE:To obtain excellent picture quality by dividing information of one line, transferring the result to plural horizontal shift registers, and adding and subtracting the outputs to obtain a color difference signal and a luminance signal. CONSTITUTION:A color separation filter 15 is adhered on an image pickup section of CCD. The color separation filter 15 consists of, e.g., a yellow transmission Ye, a cyan transmission Cy, a white transmission W and a green transmission G filter. Electric charges corresponding to the Ye filter and the W filter among the electric charges from the image pickup section are transferred respectively to a horizontal shift register 30, and the electric charge corresponding to the Cy filter and the G filter are transferred to a register 50 through a register 30. The color difference signal and the luminance signal are formed by subtracting and adding the output signals of the registers 30, 50.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to an imaging device using a solid-state imaging device. (Prior Art) Conventionally, this type of device has been equipped with an X-Y address type solid-state imaging device called a MOS type. , interline type COD,
Frame transfer type CCDs etc. are often used0 Among these, frame transfer type CODs have a structure that does not require vertical transfer registers or switching elements in the imaging section compared to MOS type or interline type ones. It is easy. Therefore, the number of horizontal pixels can be increased in the horizontal direction of the TV screen.

FIG. 1 is a diagram showing the configuration of such a conventional frame transfer type COD, in which there is an imaging section 10 that performs photoelectric conversion and a memory section 20 for temporarily storing charges from the imaging section.
, a horizontal shift register 60 that transfers accumulated charges from a part of the memory in accordance with TV synchronization, and an output amplifier 40 that reads out the charges as a voltage signal. On such 00D, optical means such as color separation filters necessary for forming color signals are provided on-chip, for example. Here, we will discuss COD of a frame transfer method using a stripe filter having R (red), G (green), and B<blue> filters.0 In the case of a stripe method and the number of pixels in the horizontal direction is approximately 580 elements, The horizontal transfer frequency corresponds to 10.7 MHsa, but when using a COD with this number of elements, the output signal of the COD is usually obtained as a luminance signal through a high-band low-pass filter (approximately 3 MHz), and R, In many cases, color separation is performed using sample-and-hold circuits for the G and B signals, each having a repetition frequency of 3.513 MHsg.

In this case, the color signal is 500K in the NTSC system.
Although a Hi band is required, in this example, the sampling frequency is 3.58 MH2, and the signal band can be reproduced up to the Nyquist frequency, so there is no problem. However, regarding the luminance signal, if the subject is close to achromatic, there is no problem, but if the subject is highly saturated in one color, the sampling frequency is 1.
58 MHg (Nyquist frequency 1.8 MHz) Ic, a considerable amount of aliasing distortion occurs, significantly degrading the image quality. In order to solve this drawback, the number of horizontal pixels should be set to 770, for example, and C.
All you have to do is drive the OD. In this way, the sampling frequency is approximately 4.77 MHz (Nyquist 2.4
MHg), which is not a problem in a normal receiver (ゝ0) However, in a 14MH2 compatible COD, the following problem occurs in the horizontal shift register, output amplifier, clock IC, and color separation sample and hold circuit.

First, in order to separate the color signals JG and B from the output signal of the COD, the period must be long enough to obtain valid signal components of the 14 MH2 signal. However, if a drive pulse with a duty ratio of 50% is used, the signal component will take 35ns, but if you subtract the rise and fall times of switching in the drive circuit, the period during which an effective signal can be obtained is at most 25n8. turn into. Also, if the clock rises and falls are too sharp, dark current will increase due to heat inside the shift register, and the effective signal period will become even shorter, and the effect of the frequency characteristics of the output amplifier must also be considered. .

Further, there is a drawback that variations in the ripple signal generation section and temperature fluctuations act synergistically, making sampling extremely difficult.

For example, if we consider a one-phase drive type horizontal shift register, each virtual electrode section includes a potential well section and a Paris 7 section, so if the number of elements is 770, K Huff 70 x 4 = 308 Of ) m-divided electrodes are required.The trick to make this possible with a 2/6' image sensor is that the horizontal width is 8.8 mm, so the minimum electrode width is less than 2.8 μm, which is currently the case. The 3 μm rule, which is considered possible, is not enough.

In addition, in order to supply the constituent lines of the conventional sample and hold circuit for color separation, for example, each sample and hold circuit for R, G, and B, and the sampled 1iv*-tv'F signal with an appropriate waveform to these three circuits. Another drawback was that a separate sample and hold circuit was required.

In addition, in an imaging device having such a plurality of horizontal shift registers, RGBGR is used as a color separation filter.
It is conceivable that a repeating method such as .

(Objective) The object of the present invention is to provide an image sensor that can be produced using current process technology without the above-mentioned drawbacks. Another object of the present invention is to provide a solid-state imaging device that can obtain good image quality by using a color separation filter suitable for such an imaging device.

(Example) The present invention will be described in detail below based on Examples.

FIG. 2 is a diagram showing an example of an image sensor suitable for the present invention, which is provided with two shift registers for horizontal readout of a frame transfer type COD.

30.50 is this register. 40 and 60 are amplifiers for converting the output charge signals of the registers 30 and 50 into voltage signals, respectively.

Next, a method of driving the shift registers 30 and 50 will be explained with reference to FIG.

In FIG. 6, reference numeral 15 denotes a color separation filter pasted on the imaging section 1o of the COD, but here, for the sake of explanation, the imaging section 1
0 to represent the charge corresponding to each color filter transferred to the memory portion 20. In addition, as an example of the color filter 15, yellow transmission Yθ, cyan transmission C71, white transmission W
I'm thinking of a striped filter consisting of green and transparent G filters, but other color combinations may also be used.
A mosaic filter may also be used.

The charges from the memory portion are transferred to the horizontal shift register for each horizontal line. Among them, the charges corresponding to the Ye filter and the W filter are transferred to the horizontal shift register 60, and the charges corresponding to the Cy filter and the G filter are transferred to the register 50 through the register 6o. As a result, charges corresponding to Ye and W are temporarily accumulated in the horizontal shift register 60, and charges corresponding to ay and GK are temporarily accumulated in the register 50.

Therefore, the spatial frequency of the pixels of the imaging unit 10 is 14.6 MHz.
If it is equivalent to an IC, the horizontal shift register 30
and 50 will be driven by a 7.16MHz clock.

Therefore, the structure of each register is 2 when compared with the conventional structure.
Since the electrode width is doubled, the manufacturing process becomes very easy.

FIG. 4 shows Ya, Cy according to the present invention as color filters.
.

This is a diagram showing an example of a signal processing circuit when the W, G method is adopted, and 0GD60 is a driver circuit 61 that forms pulses of a predetermined voltage level based on pulses from a clock signal generation circuit 62 as a control means. Driven by. From the output amplifier of this CCD60, as mentioned above, [,Y
A dot sequential signal S1 of e and W, and a dot sequential signal S1 of (3y and G)
2 is output. These point-sequential signals S1 and S2 are subjected to an M subtractor 63 serving as a color difference signal forming means, in which the G component is removed and the signal becomes a repetition signal of color difference signals RB and R+B. The color difference signal is sent to the next stage sample hold circuit 6.
4.65 separates the R-B and R+B signals and leads to a low-pass filter 66.67 that removes clock noise. The low-pass filters 66 and 67 are based on the normal NTSC standard (1
Although this filter has a pass band of about MHz, the repetition rate of the R-B and R-1-B signals in this example is 3.58 MHz.
2, a color difference signal with high color fidelity can be obtained.

Since the J/CR-B and Fl-)-B signals have been obtained up to this point, color signals R and B can be created by adding and subtracting these signals. Adder 68 and subtracter 69 function for this purpose.

Next, we will explain how to create a luminance signal. The luminance signal can be obtained by adding the point sequential signals S1 and 82 using an adder 70 serving as a luminance signal forming means to obtain the original spatial sampling phase (i.e., Ye,
Gy, W, G phase), the clock noise is removed by a low-pass filter 71 to obtain a 4.2MH2 pseudo luminance signal Y.0 In the above case, the horizontal shift register 3
When 0 and 50 are driven in the same phase, a half-pitch of the horizontal shift register drive frequency is generated between the CCD output S2 and the adder 7o, that is, FIG. FIG. The illustration (a) shows a complementary color signal Ye,
Gy, W, GK: R:G:
B'' represents the case of 1:1:1, and as is clear from this figure, it is a relatively well-balanced luminance signal.The low-frequency components of this luminance signal are averaged to some extent by the filter. However, considering it as a band signal of about 1 MHg necessary for color reproduction, Y=R+2G+B==0.25
R+0.5G+0.25B, which is a signal that approximately matches the KNTSC standard.

Incidentally, in this case, the transmittance of R, 0, and B can be adjusted to some extent by designing the color filter, and the sensitivity of solid-state imaging devices is usually lower for B than for C and RK.

Diagram (1)) a Due to the above-mentioned reasons, the sensitivity of B is changed to R and GK.
This is a schematic diagram of a luminance signal when the luminance signal is set to half of that of the
At this time, the composition ratio of R2O and B becomes even closer to Y of the NTSC standard. That is, at this time Y=0.29R+0.57G+
It becomes 0.14B.

Furthermore, since the luminance signal of this example includes all the G components in the baseband, the resolution is very high, and since the R component is modulated at 7.16 MHz, the brightness signal can be completely reproduced up to the Nyquist frequency of 3.58 MHz. However, since the B component is a modulated signal of 3.53 MHz, aliasing distortion may occur above 1.79 MHz, but the proportion of the B component in the luminance signal is (There is no practical problem because the modulation level is small. Therefore, the luminance signal band completion is 4.5 to 5.
When MHz is obtained, it becomes K. As described above, the NTS
Now that we have obtained the color signals R and B and the pseudo-luminance signal Y necessary to generate signals such as C, we need to perform signal processing such as DC reproduction, gamma correction, and white clipping on these signals using a process circuit. The luminance signal Y' is converted into a color difference signal RY,
By creating B-Y and connecting it to an encoder circuit (not shown), it becomes an NTSC signal.

FIG. 6 is a color filter diagram showing a second embodiment of the present invention in which the color filter configuration is changed. This embodiment is particularly suitable for a frame transfer type CCDK, and in the first field, when charge is accumulated, the image pickup unit charge is added as shown in the figure odd, and in the second field, the charge in the direction of the arrow shown in the figure evan is also added. Therefore, the CCD output signal is Ye, O
y, W, Cx tonal o Note that 100 in the figure indicates one pixel, and by switching the bias voltage applied to the transfer electrode for each field, the potential well can be divided into 10
Figure 7 shows a third embodiment of the color filter configuration of the present invention, and the feature of this embodiment is that the mosaic filter method is adopted. This circuit has a simpler circuit configuration than the signal processing circuit of the embodiment shown in FIG.

In particular, this embodiment is most suitable for imaging devices such as electrophotography.

The operation will be explained below using the signal processing circuit block diagram in Fig. 8.The output of the GCD 60 is first a repeating signal of Ye, W from Sl in the n horizontal lines of the odd field, and ay, c from S2. Therefore, the output of the subtracter 63 as a color difference signal forming means is the color difference signals R-B, R-1-B.
A repeating signal is obtained. When this signal is passed through the next-stage low-pass filter 66, the B component is canceled out, leaving only the color signal R.

On the next lcn+1 horizontal line, as a CCD output signal,
Since repeating signals of Cy and W are obtained from Sl, and Ye and G are obtained from S2, when these signals are subtracted, the output of the subtracter 63 becomes a repeating signal of B-R, B+H,
In the end, the FiR component is canceled out and only the color signal B can be obtained.

That is, color signals R and B can be obtained for each horizontal line. The method of synthesizing the luminance signal is the same as in the embodiment shown in FIG. A line-sequential color difference signal can be obtained. By adopting the color filter of this example, a sample and hold circuit is not required, and only two low-pass filters and process circuits are required, resulting in a very simple imaging device. becomes. In this embodiment, line-sequential color difference signals are formed as L color signals, but it goes without saying that simultaneous color difference signals can also be obtained by adding a circuit.

FIG. 9 shows an example in which the color filter configuration of the embodiment shown in FIG. 7 is changed, and it is possible to obtain the same effect as described above.

(Effects) As explained above, by adopting the four-color filter suitable for K and two horizontal shift registers GODK, the color signal forming circuit can be made very simple in configuration, and high-resolution luminance signals and color reproduction can be achieved. Although it is possible to obtain a color signal with good quality, it also produces false signals because it does not utilize the correlation of the nail polishing direction.
stomach.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional frame transfer type COD, FIG. 2 is a diagram showing an example of an image sensor according to the present invention, and FIG.
FIG. 6 is a diagram illustrating a signal readout method of the illustrated element, FIG. 6 is a diagram showing a second example of a combination of filters according to the present invention, and FIG.
The figures show a second example of the method for reading out signals from an image sensor according to the present invention, FIG. 8 shows a second embodiment of the signal processing block according to the method shown in FIG. 7, and FIG. FIG. 3 is a diagram showing another example of the configuration of a color filter according to the present invention. 40.60・S-・-Output amplifier Fig. 2 10

Claims (1)

[Claims] a solid-state imaging device having a plurality of horizontal shift registers for dividing and reading out information of one horizontal line; a color difference signal forming means for generating a color difference signal from subtraction of output signals of the plurality of horizontal shift registers; and a luminance signal forming means for producing a luminance signal from addition of output signals of the horizontal shift registers.