JPH0461587A - Solid-state color image pickup device - Google Patents

Abstract

PURPOSE:To improve the resolution and to reduce color moire by reading a signal charge stored in a storage time in one field independently and adding the charge as required. CONSTITUTION:An image pickup element chip base 1 is relatively vibrated with respect to an incident optical image. When a period a center of an opening 2 of a picture element is moved is shorter than one frame period, an opening part of each picture element is regarded to be positions X1, X2 at a field A and positions X3, X4 at a field B. Then a color filter arrangement is used for the image pickup element receiving vibration to output an R or B signal for a period t1+t2 and to output a G signal for a period t2 as the field A and to output the signal G for a period t3 and to output the signal R for a period t3+t4 as the field B. Then a picture element signal of the fields A, B on a reproduced picture is displayed while being deviated so as to be in matching with an actual sampling point spacially in the horizontal direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a color solid-state imaging device that obtains high-resolution, high-quality color images using a solid-state imaging device with a limited number of pixels.

(Prior Art) In recent years, solid-state imaging devices that use a CCD or the like instead of a conventional image pickup tube have been developed as devices for capturing images. FIG. 5 shows a schematic configuration of an interline transfer type CCD image sensor.

CIl+ C2+... are photosensitive parts (photoelectric conversion parts) of two-dimensionally arranged pixels, and VT,, VT2... are vertical readout units for vertically reading out the signal charges accumulated in each photosensitive part. HT is a horizontal readout CCD that serially reads out the signal charges read out by these vertical readout CCDs VT, VT2, . . . one horizontal column at a time. Since the resolution of this type of solid-state image sensor is generally determined by the number of pixels, there is a limit to how high resolution can be achieved through structural improvements alone.

As a device that uses a solid-state image sensor with a limited number of pixels to achieve higher resolution than the conventional one, a method has been proposed in which the solid-state image sensor chip is vibrated as shown in FIG. In the figure, numeral 1 is a chip substrate of a solid-state image sensor, and for convenience, one horizontal column of pixels arranged two-dimensionally is shown.

The pixel pitch in the horizontal direction (X direction) is PH.

The chip substrate 1 is vibrated in the horizontal direction with an amplitude of P H/2 relative to the incident light image, as shown in the vibration waveform in the figure. The temporal change of this vibration is made to have a trapezoidal shape, with one frame period of the imaging operation of the solid-state imaging device as one period. At this time, the aperture 2 of the pixel of the chip substrate 1 is at the position indicated by the solid line in the first field (field A), and at the position indicated by the broken line 3 in the second field (CB field). As a result, A.

By processing the imaging signals to obtain images corresponding to the positions of the B field, it is possible to obtain a resolution twice that of the solid-state imaging device itself.

On the other hand, in order to obtain a color image signal using one solid-state image sensor, it is common to use a color filter that combines predetermined wavelength transmittance characteristics in accordance with the pixel arrangement of the solid-state image sensor. FIG. 7 shows a frequency interleaved color filter arrangement suitable for field accumulation mode. In the figure, C is cyan, W is total transmission, and Y is yellow. When such a color filter arrangement is used, signal readout in field accumulation mode is n+(n+1
), (n+2)+(n+3), (n+4)+
(n+5),..., and in B field (
n+1)”(n+2), (n+3)+(n+4)
,... becomes. By adding and subtracting the output signal thus obtained with the signal passed through the IH delay line, the red (R), blue (B), and green (G) primary color signals necessary for color signal processing can be obtained.

The R, B, and G signals obtained in this case are converted into electrical signals while being sampled with respect to the incident optical image, as schematically shown in FIG. That is, FIG. 8(a) shows the case of the R signal, where the hatched portion becomes an invalid portion with respect to the incident optical image, and the R signal is obtained in a 2PH period, which is twice the pixel pitch PH. FIG. 8(b) shows the case of the B signal, which, like the R signal, has a 2PH period. As shown in FIG. 8(C), the G signal has a pixel pitch P
This is a signal sampled at H cycles. When the sampling frequency of the G signal is fc, the frequency spectrum of the output signal obtained by scanning each pixel in the horizontal direction is as shown in FIG. That is, the R1B signal component includes a G signal 4 and a modulation component 5 whose carrier frequency is 1/2 of the sampling frequency fC, as shown in FIG. 9(a). Further, as shown in FIG. 9(b), the G signal component includes, in addition to the G signal 4, a modulation component 6 whose carrier frequency is the sampling frequency fc. The modulation component 5°6 has a sampling frequency fc or fc/2
It has sidebands above and below the center. Therefore, if a sufficient band is provided for the G signal 4 to prevent resolution deterioration, the sidebands of the modulation component overlap with the G signal as shown by the hatched area in the figure. This results in aliasing distortion (hereinafter referred to as moiré) and causes deterioration in image quality.

As described above, moire is caused by the frequency overlap of the G signal 4 and the modulation component 5.6, so in principle, the sampling frequency fC should be set high to prevent this. However, this means an increase in the number of pixels in a solid-state image sensor, which poses difficulties in the manufacturing process.

The above-described method of vibrating the chip substrate of the solid-state image sensor can substantially double the sampling frequency fc of the G signal, so it is also useful as a countermeasure against moiré. However, even with this method, moiré occurs in the R and B signals without changing the sampling frequency.

Furthermore, in an actual incident optical image, the response near f c /2, which is a frequency lower than f c, is large, which causes moiré to be noticeable. In order to reduce this moiré, it is necessary to limit the G signal band to a frequency below f c /2, but if this is done, the G
The effect of increasing the resolution by doubling the signal sampling frequency cannot be expected.

Therefore, the present inventors have already proposed the method shown in FIGS. 10 and 11 (Japanese Unexamined Patent Publication No. 174085/1985). In FIG. 10, the image sensor chip substrate 1 shows, for example, one horizontal pixel array of an interline transfer type CCD image sensor as shown in FIG. The image sensor chip substrate 1 is vibrated relative to the incident optical image as shown in the figure with a vibration waveform.

That is, in one frame period in which the A and B field periods are one period, it is vibrated in four steps with an amplitude equivalent to PH/2 (PH is the pixel pitch). Now, during the period when the center of the pixel aperture 2 is moving, that is, during the vibration waveform shown in the figure, from tl to T2
, *2 to t3, if each period from j3 to t4 is sufficiently shorter than one frame period, the aperture of each pixel will be at the positions of Xl and X2 in the A field, and at the positions of X and X4 in the B field.
They can be considered to be stationary at the respective positions.

That is, as shown in FIG. 11, there are four spatial sampling areas P1 to P4 in the horizontal direction in one frame period. Therefore, a seventh
Using the color filter arrangement shown in the figure, as shown in Figure 11, the R, B, and G signals obtained during periods t1 and t2 are outputted as the A field, and the signals obtained during periods t3 and t4 are output. The R2B and G signals, which are out of phase with these by 180 degrees, are output, and this is used as the B field to display A, G, and A signals on the reproduced image.
By displaying the B-field pixel signals while spatially shifting them in the horizontal direction to match the actual sampling points described above, it is possible to double the horizontal resolution and reduce color moiré. Note that in FIG. 11, the white areas indicate periods tl+i2 or 13+1. The solid line hatching indicates the sampling position where a signal is obtained during the entire period, the solid line hatching indicates a position where no signal is obtained, and the broken line hatching indicates a position where a low level signal is obtained only during period t1 or t4. There is.

According to this proposal, it is possible to actually increase the sampling frequency of the G signal, thereby improving the resolution. Furthermore, as for the R and B signals, the sideband components of the modulation signal have opposite phases in adjacent fields and are canceled out, making it possible to obtain a high-quality color image with less color moiré.

However, this type of device has the following problems. That is, at the end of field A, the signal charges accumulated at t and t2 are added and read out, and at the end of field B, the signal charges accumulated at t3 and t4 are added and read out. In order to improve resolution and reduce brown moiré, it is necessary to keep the ratio of tl and t2 or t4 and t3 constant. In the inventor's experiments, this ratio was t+ :t2
(t4:t3) to around 2:3 has been found to be good.

Here, in order to improve the resolution, it is better to lengthen the accumulation time of t2 (t3), but in this case, color moiré will increase. On the other hand, to reduce color moiré, t+ (t
It is best to set 4) and t2 (ti) to 1, but in this case the resolution cannot be improved that much. This is the 11th
As shown in the figure, 1. This is because the signal charges accumulated at t2 and t2 are added and read out, and therefore there is a hatched portion shown by a broken line as shown in FIG. That is, R, B
In order to eliminate the dashed line hatching and make it white in the output, the ratio of tl and t2 or t3 and t4 should be set to 1:1, but in this case, the dashed line hatching in the G output also becomes white, The effect of improving resolution cannot be obtained.

(Problems to be Solved by the Invention) As described above, conventionally, in the method shown in Japanese Patent Application Laid-Open No. 59-174 (185), there is a so-called trade-off relationship between improving resolution and reducing color moiré. It was not possible to satisfy both parties.

The present invention has been made in consideration of the above circumstances, and an object thereof is to provide a color solid-state imaging device that can improve resolution and reduce color moiré.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is that the accumulation time within one field (for example, t
The purpose is not to add and read out the signal charges accumulated in (l+t2), but to read them out independently and add them as necessary.

That is, the present invention includes photoelectric conversion sections two-dimensionally arranged on a semiconductor substrate, and a plurality of charge conversion sections that are provided adjacent to these charge conversion sections and that vertically transfer signal charges accumulated in the photoelectric conversion sections. Vertical charge transfer section and one of these vertical charge transfer sections
Two channels are provided for each channel,
A signal charge memory section that temporarily stores the signal charge transferred by the vertical charge transfer section, and a signal charge memory section provided between the vertical charge transfer section and the signal charge memory section, and a signal charge memory section that stores the signal charge of the vertical charge transfer section as a signal. a switching gate that transfers the signal charge to either channel of the charge memory section; a horizontal charge transfer section that is connected to the signal charge memory section and horizontally transfers the signal charge stored in the signal charge memory section; and the photoelectric conversion section. A color solid-state imaging device is provided with a color filter provided with a combination of predetermined wavelength transmittance characteristics on the substrate, and the vibration is within one frame in the horizontal pixel arrangement direction with respect to the substrate under the following conditions It is synchronized with the period and has multiple amplitudes within one frame period.

(2) The amplitude change time of the vibration waveform coincides with the readout operation of signal charges from the photoelectric conversion section to the vertical charge transfer section.

(2) One of the plurality of amplitudes is set at or near 172 of the pixel pitch, and the other one is set at or near 3/2 of the pixel pitch.

one frame is constituted by an even number of fields, the signal charges accumulated in a first period in one field are read out to one channel of the signal charge memory section, and the signal charges are accumulated in a second period. The present invention is characterized by comprising means for reading out the obtained signal charges to the other channel of the signal charge memory section, and means for adding and selecting the obtained image information signals for each vibration within one field. .

(Function) According to the present invention, instead of adding and reading accumulated charges at four positions of a solid-state image sensor chip (1, +12 or t3+t4), each is read out independently, and addition processing is performed as necessary. can do. Therefore, in the R1B output shown in FIG. 11, the dashed hatched portion can be made white, and in the G output, the broken line hatched portion can be made solid hatched. That is, the G signal can be extracted only from time 12 (t:l), the sampling frequency of the G signal can be doubled, and the resolution can be improved. Also, regarding R and B signals, A,
In the B field, the sideband components of the modulated signal have opposite phases.

Therefore, color moiré is canceled out and a high quality color image is obtained.

(Embodiment) FIG. 1 is a block diagram showing a schematic configuration of a color solid-state imaging device according to an embodiment of the present invention, and FIG. 2 is a timing chart showing clock pulses of each part. As shown in Fig. 1, the layout inside the solid-state image sensor chip includes photodiodes (1-1, 1-2, ~, 1-N, ~, M-N).
A first vertical CCD 20 (20
, ~20M) are formed, for example, drive terminals φ11 to φ1
4 for 4-phase drive. In the temporary memory area 40 adjacent to the area 10, there are two groups of second vertical Cs that can be driven independently of each other.
A CD (signal charge memory section) is formed. The second vertical CCD has the A group 41 (411-49) and the 8 group 42 (
42, to 428), for example, the A group 4] is the drive terminal φS^1 to φS^4, and the 8th group 42 is the drive terminal φSB
I to φsB4 are each independently driven in four phases.

The signal charge read out to the first vertical CCD is transferred to the gate 30.
A group 4 of the second vertical CCD by (301-30M)
Transfer can be performed by switching to 1 or 8 groups 42. The signal charge transferred to the second vertical CCD is transferred to the horizontal CC
It is transferred at D50 and output from the output section 60. In this embodiment, the horizontal CCD 50 is of a two-wire type with CCD registers 51 and 52. For example, signals of the A group are read out to the CCD register 51, signals of the B group are read out to the CCD register 52 register 52, and the drive terminal φH1 , φH2, the signals are read out from the semiconductor chip from the output portions 61 and 62. Note that, of course, the horizontal CCD 50 may be of a one-wire type.

The number of vertical transfer stages of the first vertical CCD is half the number of corresponding photodiodes, and the number of photodiodes (1-1, ~, M-1, 1-3, ~, M-3,...)
The signal charge of φ1. In addition, a photodiode (1-2,
~, M-2, 1-4, ~, M-4. ...) are read out to the first vertical CCD by applying field shift pulses to φ13, respectively. On the other hand, the number of transfer stages of the second vertical CCDs, A and B groups, is also made equal to the number of transfer stages of the first vertical CCD to which they are connected. Therefore, all the signal charges that have been temporally divided and transferred can be temporarily stored in the - time memory area 40.

The above is stored in a solid-state image sensor chip, and an image is formed in a two-dimensional array area 10 of photodiodes by an optical system. Generally, except for the photodiode, the light is shielded by an Al1 film. In addition, the number of vertical transfer stages of the first vertical CCD is generally half of 512 in the NTSC system, or 2
It has 56 steps.

Figure 2 shows the drive terminals φth to φ14, φSAI to φ5A.
4. Among φSBI to φSB4, φ13. which performs field shift. φ1. and shows the voltage waveforms applied to φ5A□ and φSBI.

Here, the effective period tAE of the first field period tFl
is one vertical scanning period on the TV screen.

Near the midpoint of tAE, field shift pulse φFS
Iφ, 55 is applied to the photodiode (1-1, ~
, M-1.1-3. ~． M-3, . . . ) signal charges are read out and transferred to the first vertical CCD. Next, during the vertical blanking period tAB, the field shift pulse φ1
, 2, by applying φFS3, the photodiode'<1-2.
~． M-2. l-4, ~, G4. ...) are read out to the first vertical CCD. Then φ11~φ14
A four-phase transfer lock pulse voltage (in the figure, φ11 is φ1.2, φ13 is φ6, and φSB+ is φ513) is applied to the terminals of the second vertical CCD0B group 42, and the first vertical CCD The signal charge group is transferred from there to the eight groups 42 of the second vertical CCD.

Here, A from the first vertical CCD to the second vertical CCD,
Assignment to group B is made using the terminal SG located between areas 10 and 40.
This is done by applying a pulse voltage to the switching gate 30 (having one or more terminals) connected to the switching gate 30 (having one or more terminals).

The signal read to the temporary memory area 40 is then applied to the terminals φSAI to φSA4 and φSBI of the A and B groups of the second vertical CCD during the valid period tBH of the field period tF2.
~ 4-phase transfer port to φSB4, Tsuk pulse (φS in the figure)
L3, φSL4, φSL7, φ5L8,...) is applied and the signal charges are read out one column at a time in the horizontal direction, and the horizontal C
It is transferred to the CD 50 and read out from the output section 60 using clock pulses φold and φH2. At this time, the signal of group A is CCD
In the register 51, the signals of group B are read out to the CCD register 52, and simultaneously outputted from the output sections 61 and 62. The signal charge accumulated in the photodiode during the first field period tel is transferred to the second field period tP2.
It is read within.

That is, by this operation, signals with twice the number of pixels as in the conventional method can be read out within one field period.

Then, during periods tBE and tBB, the same field shift pulses φPS3, φFS71 φPS4 r as before are applied.
φFS8, and further transfer pulse voltage (φ113° in the figure φ1,7・φmouth 2・φI,4.φshi8・φS,4
), and the valid period t of the second field period tF2
The signal charge accumulated in the BE by the photodiode is transferred to the second vertical COD of the independent temporary memory area 40 in the same route as was done in the first field period tF1. Then, it is output in the same manner in the next field period. below,
Reverse this action. This allows high-resolution signals to be output from a limited number of pixels. Note that the output section 6 in FIG.
An adder circuit 70 is provided at 1.62, and the adder output is R(B
) output, and the output of the output section 61 is set to 6 outputs.

Next, the operation of improving resolution and reducing color moiré will be explained using FIG.

FIG. 3(a) shows one horizontal pixel array of the CCD image sensor explained in FIG. 1, where 1 indicates the image sensor chip substrate and 2 indicates the aperture of the pixel.

The image sensor chip substrate 1 is vibrated relative to the incident optical image as shown in the vibration waveform in FIG. 3(b). That is, it is vibrated in four steps at an amplitude corresponding to PH72 (PH is a pixel pitch) in one frame period in which the A and B field periods are one period. Now, during the period when the center of the aperture 2 of the pixel is moving, that is, during the vibration waveform shown in the figure, from tl to t2
+ If each transient period from t2 to "3 + t3 to t4 is sufficiently shorter than one frame period, the aperture of each pixel will be stationary at the positions Xl and X2 in the A field, and at the positions X3 and X4 in the B field, respectively. It can be seen as doing so.

That is, as shown in FIG. 4, there are four spatial sampling areas P1 to P4 in the horizontal direction in one frame period. Here, as shown in 3rd e (b), each time the signal charge accumulation time tI + t2 + t3 + i4 ends,
Field shift pulses F+, F2 to read signal charges
, F3 and F4 are applied to the first vertical CCD. This pulse is the same as the field shift pulse explained in FIG. 2, and the relationship is that F, is φPSI φPS5, F
2 is φFS2・φPS6 SF 3 is φFS3・φF5
7 to F4 match φF54 and φl-58.

Therefore, by using the color filter arrangement shown in FIG. 7 on the image sensor subjected to such vibrations, as shown in FIG. 4, period 1. +12 outputs an R or B signal, period t2 outputs a G signal and makes this the A field, and period t3 outputs a G signal,
During the period t3+14, an R signal is output and this is taken as a B field. Then, by displaying the AB field pixel signals on the reproduced image while spatially shifting them in the horizontal direction to match the actual sampling points mentioned above, the horizontal resolution can be doubled and color moire can be reduced at the same time. I can do it.

As is clear from the above operation, the G signal includes only the charges accumulated during the period t2 in the A field, only the charges accumulated during the period t3 in the B field, and finally reaches t.
The reproduced image is obtained by adding the spatial sampling points 2 and t3. Therefore, the resolution can be doubled. On the other hand, R, B
The signal is 1. The spatial sampling points of t and t2 are added, and in the B field, the spatial sampling points of t and t4 are added and output.

As a result, color moiré is completely reversed between the A field and the B field, so it can be significantly reduced.

[Effects of the Invention] As detailed above, according to the present invention, the solid-state image sensor chip is vibrated, and the signal charges accumulated in the first period and the second period of the field are added and read out. Instead, by reading out the signals independently and adding them as necessary, it is possible to obtain a color image with high resolution and less color moiré.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a schematic configuration of a color solid-state imaging device according to an embodiment of the present invention, Fig. 2 is a timing chart showing clocks of each part, and Fig. 3 shows one horizontal pixel array and vibration waveform. 4 is a diagram showing sampling points for an input optical image of RlG and B signals obtained by color filter arrangement, and FIGS. 5 to 11 are diagrams for explaining the prior art. 1-1. ．． 1. -2. ~． 1-N, ~, M-N
... Photodiode, 10... Two-dimensional array area, 20 (21, 22)... First vertical CCD (vertical charge transfer unit), 30... Switching gate, 40... - time memory area , 41.42=second vertical CCU (signal charge memory section) 50 (51, 52) *Flat CCD (horizontal charge transfer section), 60 (61, 82)...output section.

Claims (1)

[Scope of Claims] Photoelectric conversion units arranged two-dimensionally on a semiconductor substrate, and a plurality of units provided adjacent to these photoelectric conversion units to vertically transfer signal charges accumulated in the photoelectric conversion units. a vertical charge transfer section, and a signal charge memory section, which is provided with two channels for each channel of these vertical charge transfer sections, and temporarily stores signal charges transferred in the vertical charge transfer section; A switching gate is provided between the vertical charge transfer section and the signal charge memory section to transfer the signal charge of the vertical charge transfer section to either channel of the signal charge memory section, and a switching gate is connected to the signal charge memory section. , a color solid state comprising: a horizontal charge transfer section that horizontally transfers signal charges stored in the signal charge memory section; and a color filter provided on the photoelectric conversion section with a combination of predetermined wavelength transmittance characteristics. An imaging device, which is synchronized with one frame period in a horizontal pixel arrangement direction with respect to the substrate, and has a plurality of amplitudes within one frame period, one of which is 1/2 of the pixel pitch or in the vicinity thereof. and the other one is set at 3/2 of the pixel pitch or its vicinity, and the amplitude change time of the vibration waveform is a means for applying vibration from the photoelectric conversion section to the vertical charge transfer section that coincides with the signal charge readout operation. One frame is composed of even fields, the signal charges accumulated in the first period within one field are read out to one channel of the signal charge memory section, and the signal charges accumulated in the second period are read out. A color solid-state imaging device comprising: means for reading out to the other channel of the signal charge memory section; and means for adding and selecting the obtained image information signals for each vibration within one field.