JPH0620317B2 - Imaging device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an image pickup apparatus using a solid-state image pickup element.

(Prior Art) Conventionally, in this type of device, an XY address solid-state image pickup device called a MOS type or an interline type C is used.
CDs, frame transfer CCDs, etc. are often used. Among them, the frame transfer type CCD is structurally very simple as compared with the MOS type and the interline type, because it is not necessary to provide a vertical transfer register in the image pickup section. Therefore, it is possible to integrate a large number of horizontal pixels corresponding to the horizontal direction of the TV screen.

FIG. 1 is a diagram showing such a conventional frame transfer type CCD. An image pickup unit 1 that performs photoelectric conversion, a memory unit 2 that temporarily stores charges from the image pickup unit, and further accumulated charges from the memory unit. In accordance with TV synchronization, is composed of a horizontal shift register 3 for transferring charges and an output amplifier 4 for reading the charges as a voltage signal. CC like this
On D, a color separation filter necessary for producing a color signal is adhered or on-chip.

FIG. 2 is a diagram showing an example of the filter. Here, R (red), which is said to have very good color reproducibility,
A conventional frame transfer type CCD using a G (green) and B (blue) stripe system will be described.

When the number of pixels in the horizontal direction of the stripe method is about 580 elements, the horizontal transfer frequency corresponds to 10.7 MHz. When a CCD with this number of elements is used, the normal luminance signal is CCD.
The output signal of the high frequency band low frequency filter (about 3 MHz)
z), and as a color signal, R. G. In many cases, the B / signal repetition frequency of 3.58 MHz is separated by each of the sample and hold circuits. In this case, NTSC requires a band of 500 KHz, but
In this embodiment, the sampling frequency is 3.58MHz,
There is no problem because the signal band can be reproduced up to the Nyquist frequency. However, regarding the luminance signal, there is no problem if the subject image is close to achromatic color, but for the subject image with high color saturation, the sampling frequency is 3.58MHz (Nyquist
Since it becomes 1.8MHz), there will be a considerable amount of aliasing distortion and the image quality will be significantly degraded. In order to solve this drawback, it becomes necessary to drive about 770 horizontal pixels, that is, 14 MHz. With such a CCD compatible with 14 MHz, the sampling frequency becomes about 4.77 MHz (Nyquist 2.4 MHz) even in the case of the special subject image described above, and the aliasing distortion can be remarkably reduced. Then it does not matter at all.

However, in the CCD compatible with 1.4 MHz, the following problems occur on the horizontal shift register, the output amplifier, the clock IC, and the color separation sample and hold circuit.

First, the color signal R. G. In order to separate B, the period of the portion corresponding to the effective signal component of the 14 MHz signal must be long to some extent. However, when the drive pulse with a duty ratio of 50%, the signal component is calculated However, in actuality, the rise due to the components of the drive circuit,
If the fall time is about 10 ns in total, the remaining part is about 25 ns. Furthermore, the rise of the clock,
If the trailing edge is too steep, the dark current increases due to the heat generation of the shift register, and the effective signal portion has a shorter period. Further, if the frequency characteristics of the output amplifier are also taken into consideration, the effective signal period becomes shorter. In this way, in the 14MHz CCD, the period of the signal component becomes considerably short, and the fluctuation of the element of the clock generation part or the fluctuation of the sample pulse due to the temperature fluctuation is also added.
There is a drawback that it becomes difficult to separate signals. Also 770 element C
For example, it is quite difficult to integrate a CD as a horizontal shift register of a 1/2 ″ size image sensor at the present time. Further, when a horizontal 770 element is driven at 14 MHz in this way, 2 When sampling is performed with a striped filter as shown in the figure, as described above, the Nyquist frequency of each color signal is 2.4 MHz, which is usually sufficient, but in order to obtain a higher quality image signal, This is still insufficient, especially in printers and high-definition televisions.

(Purpose) A first object of the present invention is to provide an imaging device capable of solving the above-mentioned drawbacks of the prior art.

A second object of the present invention is to provide an image pickup device and an image pickup device which can omit the sample and hold circuit configuration for color separation.

A third object of the present invention is to provide an image pickup apparatus capable of accurately performing color separation of an image sensor having a large number of horizontal elements.

A fourth object of the present invention is to provide an image pickup device capable of forming an image signal with high resolution and good color reproducibility.

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

In the present embodiment, in order to eliminate the above-mentioned drawbacks, a conventional CCD having one horizontal shift register is not used, but FIG.
The problem described above is basically solved by using a CCD having two horizontal shift registers as a read transfer path as shown in (1) and halving the horizontal transfer frequency. That is, the pixel charge in the horizontal direction is transferred to the clock generation circuit 4 shown in FIG. 6 or 7.
6, the horizontal transfer frequency is halved by transferring to the two horizontal shift registers at a period of 1 pixel.

In this case, although the frame transfer type CCD is described in the embodiment, the same applies to the interline transfer type CCD, of course.

In this embodiment, the color filter of FIG. 3 (b) is attached to the CCD of FIG. 3 (a), and the charge of each cell of one horizontal line is applied by the clock circuit 46 of FIGS. 6 and 7 described later. Are driven so as to be distributed to the registers 31 and 32 cell by cell. As a result, at the outputs S1 and S2 of the first and second shift registers 31 and 32, G and R signals are respectively accumulated for the nth line as shown in FIG. 3 (b), and the (n + 1) th line is accumulated. For the eyes, B and G signals are stored respectively. Further, each of the registers 31 and 32 is driven by a horizontal transfer pulse whose phase is shifted by 180 °. The clock generation circuit 46 is a CCD
Horizontal transfer, and also functions as control means for controlling the distribution of charges to the registers 31 and 32.

FIG. 6 is a diagram showing an example of a signal processing circuit for forming the Y, (RY), and (BY) signals from the first and second register outputs S1, S2. Shift registers 31, 3
The signals S1 and S2 output from the circuit 2 are amplified by the amplifiers 5 and 6 and then passed through the 1H delay lines 7 and 8, respectively, to generate signals delayed by one horizontal period. Considering here the G signal, as shown in FIG. 3 (c), the G signal of the n line is stored in the shift register 31, and the G signal of the (n + 1) line is stored in the shift register 32. Since the signals on the n-th line and the (n + 1) -th line are matched with the spatial sampling, the clock cycle is set so that the signals are read out by shifting by half cycle as described above at the time of reading. Here, the line switch 9 selectively switches between the signal of S1 and the signal of 1H (horizontal period) delay every 1H,
A synchronized signal is obtained for each horizontal line. Similarly, the line switch 12 obtains a signal synchronized with each line from the signal of S2. These signals are added by the adder 14.
The added signal has a double sampling rate after the addition because the G signals of S1 and S2 are shifted by 1/2 cycle. The output signal of the adder 14 is supplied to the low pass filter 1
After passing through 5, the clock pulse is removed and then amplified by the amplifier 19. Since this signal has a high sampling rate as described above, it becomes a wideband G signal and is referred to as GW.

On the other hand, the signal of S1 and S2 is halved by the line SW10.
By selecting f _H (f _H : horizontal scanning frequency),
It is possible to obtain a G signal that matches the spatial sampling of one line. This signal is passed through a low-pass filter 16 to remove the clock pulse and then amplified by an amplifier 20 to obtain a G signal G _L having a band narrower than the signal G _W.

As for the R and B signals, as shown in FIG. 3 (d), the B signal is stored in the shift register 31 and the R signal is stored in the shift register 32 every 1H.

Since the B signal is output to S1 only every 1H, the 1H delay signal and the original signal are switched and selected by the line switch 11 for every 1H, and are simultaneously read out for each line. By passing this signal through the low-pass filter 17, the clock signal is removed and the B signal is obtained.

Similarly, the R signal is simultaneously read from S2 by the line switch 13. This signal is removed by the low pass filter 18 to obtain an R signal.

The R, B, and G _L signals thus obtained are processed.
Input to the matrix circuit 23, _{Y L} signal and color difference signals _(R-Y L), while making the _{(B-Y L),} the subtraction circuit 21
Then, the G _L signal is subtracted from the wide band G signal G _W described above to obtain G
To produce the high frequency signal _GH . Such a G _H signal obtained by the, G _{L, B,} R, and Y _L signal produced from the signal by the adding circuit 22, to obtain a Y signal as the luminance signal by adding. In this way, the NTSC luminance signal Y having the entire band
Is formed. Further, the luminance signal Y and the color difference signal RY
_{The L} , B-Y _L signals are led to an encoder (not shown) to become NTSC signals. If this NTSC signal is connected to a display, a high quality image with good color reproducibility can be obtained.

Incidentally, FIG. 4 is a main part configuration diagram of an example of the image pickup device shown in FIG. The diagonal line on the right is a channel stop,
A and B indicate virtual electrode portions, and C and D indicate portions below the transfer electrodes. 117 is a separation part for sequentially separating the line information of the memory part into two registers 31 and 32,
The gate electrode may be used for separation. Two
E is a transfer electrode of the memory unit 2. 17E is a transfer electrode of the separation unit, and 31E and 32E are registers 31 and 32, respectively.
, CL is a clear gate portion, and CD is a clear drain.

In this embodiment, one-phase driving is used, but a driving method of two or more phases may be used. Also, the potentials P (A) to P of the portions A to D
(D) is always Therefore, when a high level voltage is applied to each transfer electrode, P (C)> P (D)> P (A)> P (B), and when a low level voltage is applied, P (A) > P (B)> P (C)> P (D).

Since it is configured in this way, the memory unit 2
The charges on 168 and 171 move to 167 and 170, respectively, by making the clock φ _T high, and then to 166 and 164, respectively, when φ _T goes low again. After that, when the clock φ _{1 is set} to high level, the charge of 164 moves to 163,
When the clock φ _{2 is set} to the high level, the process moves to 161, and the clock φ ₂ is accumulated at 160 after the trailing edge of the clock φ ₂ .

On the other hand, if a pulse is supplied to the clock φ _T again while the clock φ _S is kept at the low level, the charge applied to 166 is 164
Move on to. After that, the charge of 164 moves to 162 by supplying the clock φ ₁ for one pulse.

In this way, one horizontal line of information in the memory section is divided and moved to the registers 31 and 32, and then one line is shifted again in the memory section, and then the above sequence is repeated. The information can be read out by dividing one horizontal line by two shift registers.

The horizontal transfer by the registers 31 and 32 may be performed by an appropriate method.

Next, FIGS. 5 (a) to 5 (c) and FIG. 7 are views showing a second embodiment of the present invention. FIG. 5 uses a W (transparent filter) filter in place of the G filter shown in FIG. 3 (b), and FIG. 7 shows its signal processing circuit. Similar to the above-described filter system, R and B can be separated in the same manner as a blink. The signal transmitted by the W filter is the above-mentioned G
Although it corresponds to a signal, since the W filter is a transparent filter, light passing through it can be treated as a Y signal (luminance signal). For the Y signal, Y _W (wideband Y signal) and Y _L (low band Y signal) corresponding to the above G _W and G _L can be obtained. Y _L ,
R, B make at process the matrix circuit 25 the color difference signals _R-Y L, the _{B-Y L.} The NTSC signal him Shirubebi to (omitted in the drawing) Encoder These color difference signals and Y _W signal.

Adopting such a filter structure has the effect of increasing the light utilization rate and increasing the sensitivity.

Next, FIG. 8 is a diagram showing a third embodiment of the present invention. In this embodiment, the outputs of the registers 31 and 32 are recorded independently of each other without being subjected to correlation processing. , S2 are input to the line switches 100 and 101 after passing through the amplifiers 5 and 6, respectively. This line switch 10
0 and 101 are switched by the clock generation circuit 46 every 1/2 f _H.

Further, 102 and 105 are low-pass filters, 103 and 106 are process circuits, 104 and 107 are modulation circuits, 108 is a mixer, 109 is a recording circuit, 110 is a recording head, 111 is a recording medium, and 112 is a line switch. It can be switched at 1/2 f _H. Reference numeral 113 is an oscillator which outputs carriers f ₁ , f ₂ and f ₂ ′.

Further, the head 110 switches the recording track every 1H. With this configuration, the G signal is recorded by 1H at a time, and the R signal and the B signal are recorded line-sequentially. here,
For example, the modulation circuits 104 and 107 are FM circuits, and f ₁ is a number.
MHz, f ₂ and f ₂ ′ are set to several hundred KHz, respectively.

With this configuration, the resolution in the vertical direction is slightly reduced, but the band of each color signal is at the Nyquist frequency 3.
Since it spreads to 58MHz, color reproducibility is extremely good. Further, since the vertical and horizontal correlations are not used, no false signal is generated.

(Effect) As described above, according to the present invention, (1) the sample hold circuit for color separation can be omitted or simplified.

(2) It is possible to prevent a decrease in S / N that accompanies high-speed reading of the horizontal shift register, and reduce inaccuracy when separating a color signal from a dot-sequential signal.

(3) The driving frequency of the horizontal shift register can be substantially reduced.

(4) Since only two horizontal shift registers are used, the configuration is simpler than when a horizontal register is provided for each color.

(5) The processing circuit configuration of the output of the image sensor is simplified by matching the repeating pattern of the color filter and the distribution cycle of the horizontal line signal to both shift registers. Image quality with sensitivity is obtained.

(6) Since a checkerboard-shaped color filter is used, the sampling frequency of each color can be increased, and since signal processing is performed without using vertical correlation, a wideband color signal can be obtained and color reproduction is possible. It is also excellent in that false signals are less likely to occur.

(7) Of course, if vertical correlation is used, there are many effects such that a high-frequency luminance signal and a standard color television signal can be easily formed.

[Brief description of drawings]

Figure 1 is a block diagram of the frame transfer CCD, and Figure 2 is the RG.
FIG. 3B is a diagram showing an example of a repeating color filter B, FIG. 3A is a configuration diagram of an image pickup device suitable for the present invention, and FIG. 3B is a color filter suitable for the present invention and distribution of horizontal line signals. FIG. 3 is a diagram for explaining the method, FIGS. 3 (c) and 3 (d) are diagrams for explaining color separation of the present invention, and FIG. 4 is a configuration diagram of a main part of an example of an image sensor, FIG.
(a), (b) and (c) are diagrams for explaining a method of distributing a second color filter and horizontal line signals suitable for the present invention, and FIG. 6 is a block diagram of a signal processing circuit according to an embodiment of the present invention. FIG. 7 is a signal processing circuit block diagram of the second embodiment of the present invention, FIG. 8 is a signal processing block diagram of the third embodiment of the present invention, 5, 6 are amplifiers, 7 and 8 are 1H delay lines. , 9 to 13 are line switches, 14 is an adder, 15 to 18 are low-pass filters, 19 and 20 are amplifiers, 21 is a subtraction circuit, 22 is an addition circuit, 23 is a process matrix circuit, 24 is a process circuit, and 25 is Process matrix circuit, 10
4, 107 is a modulation circuit.

Front Page Continuation (56) References JP-A-55-35536 (JP, A) JP-A-57-28480 (JP, A) JP-A-56-154892 (JP, A) edited by the Television Society, "Television, Image Engineering Handbook ", Sho 55, 12, 30, P. 257

Claims (1)

[Claims] 1. An image pickup means for photoelectrically converting image pickup light from a subject, and two kinds of color filter portions provided in a light path incident on the image pickup means in a predetermined repetitive arrangement in each horizontal line. Color separation filters are arranged such that one kind of color filter portion is arranged between each horizontal line and shifted by one pixel for each horizontal line, and information on each color in each horizontal scanning line from the image pickup means. Two horizontal transfer means for dividing into two and reading out for each color, and a recording means for independently recording each color information output from these horizontal transfer means on a disk-shaped recording medium without correlation processing. An imaging device comprising: