JPS6020955B2 - Color solid-state imaging device - Google Patents

Description

Detailed Description of the Invention The present invention provides a single-chip color solid-state imaging device that uses a single solid-state imaging device to obtain color images, in which color filter elements having three types of spectral characteristics are repeatedly arranged in the horizontal direction. The color filters of the structure spatially modulate the colored light corresponding to the three types of color filters, and the vertical transfer stage of the Oka body image sensor is The purpose of this is to minimize the influence of transfer efficiency on image quality.

Traditionally, solid-state imaging devices include charge transfer devices such as CCDs.
There are two types: (chargeable device) type or BBD (bucket brigade device) type, and MOS type with ×1Y address element. Among these, MOS type solid-state image element uses a shift register to connect MOS type transistors. Due to sequential switching, spike noise occurs due to switching pulses, especially in the horizontal scanning direction, and as the number of pixels increases, this spike noise increases with respect to the signal and controls the S/N. . However, since such solid-state image sensors read out signal charges from pixels by addressing them, it is said that there is no effect due to the adjacent vertical position, and a mosaic color filter as shown in Figure 1 is used. However, it was thought to be suitable for color systems that utilize vertical correlation to obtain color signals. However, as the number of horizontal pixels increases, the time constant for high-speed switching for horizontal addressing becomes impossible to maintain.
As a result, charges are left behind in the vertical signal line, so when the filter shown in FIG. 1 is used, a problem of color mixture occurs in the vertical signal line. In addition, the part indicated by the dotted line in Fig. 1 is the photodiode of the light receiving section.
Solid lines indicate color filter elements. In addition, the CCD has a frame transfer method in which the signal charge of the light receiving section is transferred at high speed to the storage section for each frame and sequentially read out from the storage section through a horizontal transfer stage, and a frame transfer method in which the signal charge of the photodiode is transferred every vertical line. There is an interline method, in which signal electrodes are read out on independent vertical transfer lines, transferred to a horizontal transfer stage every horizontal scanning period, and sequentially extracted as a serial signal from this horizontal transfer stage.The former frame transfer method In this case, since the channel stopper exists only in the vertical direction, crosstalk occurs in adjacent vertical directions, making it impossible to use a color method that utilizes vertical correlation. G. It is necessary to use the B stripe color filter to create a color system that does not cause color transfer even if there is crosstalk.

However, this method has the disadvantage that high resolution of the luminance signal cannot be achieved because the color filters are repeated every three. Furthermore, in the color system as shown in FIG. G.
By inverting the B color filter every horizontal scan, it is possible to cancel the spatial modulation components that occur outside the color filter.
Although there is no reduction in the resolution of the luminance signal, crosstalk in the vertical direction causes warm colors.

In addition, in the case of the interline method, the photodiodes, which are the light receiving sections, exist separately, so although it is possible to use the mosaic color filter shown in Figure 1,
Since the transfer efficiency of the vertical transfer stage was not 100%, a moat color was caused by the components left behind.

The present invention was developed to solve these problems, and the color solid-state imaging device according to the present invention will be described below with reference to the drawings of FIGS. 4 to 10.

FIG. 4 shows the structure of a solid-state image sensor, which is one of the components of the color solid-state image sensor of the present invention. In the figure, 1 is a chip of this solid-state image sensor, 2 (2a, 2b,
2c...) is a photodiode which is a light receiving section.

Usually, this photodiode 2 is formed by a PN junction, and substantially the centers of this photodiode 2 are arranged in a staggered manner. 3 (3a, 3b,
3c...) is a vertical transfer stage, which is usually composed of a CCD, but since the vertical transfer frequency is low, it is also possible to use a BBD.

As shown in FIG. 4, the relationship between the photodiode 2 and the vertical transfer stage 3 is such that signal charges are taken out to the vertical transfer stage 3 in the opposite direction for each horizontal line. That is, the photodiode 2a of the first horizontal line in FIG.
is connected to the vertical transfer stage 3a, and the photodiode 2b of the second horizontal line is connected to the adjacent vertical transfer stage 3b.

Further, a gate is provided between these photodiodes 2 and the vertical transfer stage 3, and the vertical BLK
It is designed to be open only during certain periods. The signal charge from the photodiode 2 read out to the vertical transfer stage 3 in this manner is transferred upward one stage at a time every -horizontal period by the vertical transfer pulses 0v·, ◇v2.

These vertical transfer pulses ◇v, , Jv2 differ depending on the configuration of the vertical transfer stage 3 for 2-phase, 3-phase, and 4-phase cases, but in the case of 2-phase as in this example, they are 180° inverted from each other. That's fine. These signal charges sent upward from the vertical transfer stage 3 are read into the horizontal transfer stage 4 during the horizontal BLK period,
Then, the read signal charges can be sequentially transferred by the horizontal transfer pulses JH2 and OH2 and read out in series, so that they can be taken out from the output terminal 5. The clock frequency of this horizontal transfer is determined by the number of pixels in which the photodiode 2 is arranged horizontally.
In the case of 84 pixels, approximately 7. It is a contribution. 5 shows an example of a color filter installed on the solid-state image sensor shown in FIG. 4. In the example shown in FIG. 5, a green (G) filter is placed on the photodiode 2 shown in FIG. 6. This is an example of a striped color filter in which a red (R) filter 7 and a blue'B filter 8 are arranged in sequence.

When the photodiode 2 and the filter are arranged in this way, the photodiodes 2a,
2a', 2a''... to R.○.B filter 6, 7, 8
A spatially modulated signal is obtained, and in the second horizontal line, photodiodes 2b, 2b', 2b''...
Thus, a spatially modulated signal having a phase difference of 1800 with respect to the signal of the first horizontal line is obtained.

Fig. 6 shows an example of a color filter configuration in which the light receiving part of the solid-state image element is not only a photodiode with a PN junction, but also a light fin conversion film to increase the effective area of the light receiving part. This is what is shown.

In Figure 6, 9a, 9a', 9a''...9
b, 9b', 9b''... and gc, 9c', 9c''...
...are photodiodes 2a, 2a', 2a''... in Fig. 4.
...2b, 2b', 2b''...2C, 2c', 2c''...
PN junction photodiode compatible with 10a, 1
0a'. 1 0a''....1 0b, 1 0b', 1
0b″...and 10c, IOC, 10c″
... is photodiode 9a, 9, 9a^'...9b
,9b',9b''...9c,9c',9c''...
These photoelectric conversion films 10a, 10a', 10a''...10b, 10
b', 10b''...10c, 10c', 10c''...
A red (R) filter 11, a green (G) filter 12, and a blue tB' filter 13 are installed substantially glued to.... In the case of this embodiment, the color filter does not have a stripe shape as shown in FIG. 5 described above, but a mosaic color filter, but the effective light-receiving area becomes larger, compared to the case of using only a PN junction photodiode. Sensitivity can be significantly improved. FIG. 7 shows a specific example of the photodiode section and the vertical transfer section of the solid-state image sensor described above. In FIG. When a pulse ◇p is applied to the gate 16, the signal charge of the photodiode 14 is read out in the direction of the dotted arrow.

In the case of two phases, the vertical transfer section 15 is covered with transfer electrodes 16a and 15b made of polysilicon, and receives vertical transfer pulses V, V,
, ◇v2 is applied, the data is transferred in the direction of the solid arrow. In addition, since each photodiode 14 is provided with a channel stopper 17, crosstalk does not occur between each photodiode 14, and since the photodiode 14 has a filter configuration as shown in FIG. The signal charges caused by the filters are read into separate vertical transfer stages and transferred in a predetermined direction, so that even if the transfer efficiency is low, no warm color is produced. FIG. 8 is a block diagram of the electrical signal processing circuit of the color solid-state imaging device of the present invention. In FIG. 8, 18 is a solid-state image sensing device to which the above-described structure and color filters are glued. 19
is a synchronous signal generator, and it is convenient to use a frequency four times the original oscillation frequency of 3.58 digits. This synchronizing signal generator 19 generates pulses ◇v・, ◇v2, OH,, J
H2,? A drive signal for the solid-state image sensor 18 such as p is generated by a drive circuit 20 and supplied to the solid-state image sensor 18 by V. The output signal of the solid-state image sensor 18 is delayed by Δt for each horizontal time by delay lines 21 and 22 of Δt and changeover switches 23 and 24. This is because the photodiodes are arranged in a staggered manner, and the color filters are arranged so that the spatial modulation signal is inverted every horizontal scan, but since the same color signal passes through the same vertical transfer stage, the solid-state image element This is because the output from the child 18 is read out at the same timing, so in order to correct the spatial position and the phase of the spatially modulated color signal, it is necessary to correct the modulated color signal by a time corresponding to 1800. . This relationship was shown by
9a to 9c, and if the modulated color signal by the color filter during the 2-day scanning period is the vector shown in FIG. 9a, then (n+
1) Even during the H scanning period, as described above, the phase becomes evening as shown in FIG. 9b with the same phase.

This is delayed by 180 degrees to obtain the phase shown in FIG. 9c. This signal is changed to 1 by the changeover switches 23 and 24 so that the arrangement of the photodiode matches the timing of the output signal.
They are alternately switched every horizontal scanning period, and only one of them is passed through the IH period delay line 25 and is supplied to an adder 26 and a subtracter 27 together with the output of the other. FIG. 10a shows the signal spectrum of the (n+1) H scanning period obtained at the output terminal of the changeover switch 24, and FIG. 10b shows the signal spectrum of the IH period delay line 25.
This figure shows the signal spectrum during the evening NH scanning period.

Moreover, in FIG. 10, s is the sampling frequency of the pixel, and s is the spatial modulation frequency by the color filter. Here, in the adder 26, the signals of the calm and negative (n+1) day horizontal scanning periods are added together, but the color signals are canceled because their phases differ by 1800, while the luminance signals are processed in a staggered manner by the photodiodes. Because of the arrangement, aliasing distortion is also canceled out and taken out.

The spectrum of this signal is shown in FIG. 10c.
That is, the output signal of the adder 26 has unnecessary components removed by the first low-pass filter 28, and is applied to the encoder 30 by the delay line 29 after matching the delay time with the color signal.

On the other hand, when the subtracter 27 selects 0, since there is a large correlation between adjacent horizontal scanning lines, only the modulated color signal components spatially modulated by color filters having phases different by 1800 are extracted. The spectrum of this signal is shown in FIG. 10d. This modulated color signal is input to first and second synchronous detectors 32 and 33 with unnecessary components removed by a bypass filter 31 and with a band width limited to 0.9 MHz. When the reference signal generated by the synchronous signal generator 19 is applied to these synchronous detectors 32 and 33 at a specific phase, color difference signals of RY' and BY' are obtained. The phase difference between the reference signals applied to these two synchronous detectors 32 and 33 is given by a phase shift difference 34. The color difference signals detected in this way are subjected to second and third low-pass filters 35 and 36, in which ominous true components are removed.
It is applied to the encoder 30 together with the luminance signal.

The encoder 30 also receives a burst signal and a synchronization signal from the synchronization signal generator 19, converts it into an NTSC composite color signal, and outputs it from an output terminal 37. In this specific example, Δ
Although the delay line 25 of t is used, instead of this, the timing of the horizontal clock of the horizontal transfer stage of the solid-state image sensor 18 may be shifted by this amount. Further, even if cyan or the like is used for the blue leg of the color filter, it is sufficient if the demodulated color difference signal can be processed by the demodulation axis, near matrix, or the like. Further, this can be similarly implemented in the case of a MOS group image sensor. The explanation was given using an example of synchronization using an IH period delay line, but if it is a MOS type, it is structurally possible to output multiple lines at the same time, so there is no need for synchronization using an IH period delay line. . As described above, according to the color solid-state imaging device of the present invention, the following effects can be obtained.

'1} R. ○． Since spatial modulation is performed using three color filters such as B, the signal processing circuit becomes simple. ■R. G. Since three color filters such as B are used, each spectral characteristic can be set relatively easily, and color reproducibility is also good.

{3' The aliasing distortion due to photodiode sampling can be removed.

{41 Even if a three-color filter is used, the resolution of the luminance signal can be high because the spatially modulated modulated color signal components are canceled out.

'5' Since no other color signal component is read into each vertical transfer stage, a warm color will not be obtained even if there is a component left behind due to transfer efficiency or the like.

'61 Since the same type of filter is used for each horizontal line, line crawl and flicker do not occur.

'71 2 with identical color filter elements aligned vertically
Since one common vertical signal line is provided for the light receiving section array of the book, the area of the light receiving section can be increased, the sensitivity can be high, and it is also suitable for high density.

Even if the color filter elements are not arranged in a square arrangement, the number of vertical signal lines is the same as in the case of a square arrangement, and even if the number of pixels increases, the width of the vertical signal line does not need to be made thinner, and the dynamic range will not decrease. do not have.

[Brief explanation of drawings]

1 to 3 are schematic diagrams for explaining the color filters directly in the color solid-state imaging bag, respectively, and FIG. 4 is a schematic diagram of a solid-state imaging device in a color group imaging device according to an embodiment of the present invention. 5 and 6 are schematic diagrams for explaining examples of color filters in the same device, and FIG. 8 is a block diagram showing an electric circuit in the same device, FIGS. 9 a to c are vector diagrams for explaining the functions of the figure parts in the block circuit of FIG. 8, and FIGS. 10 a to d are schematic diagrams. FIG. 9 is a diagram showing a signal spectrum for explaining the function of main parts in the block circuit of FIG. 8; 2, 2a, 2a', 2a'', 2b, 2b', 2b'', 2
c, 2c', 2c'', 9 a, 9a', 9a'', 9
b, 9b', 9b'', 9c, 9c', 9c'', 14...
Photodiode, 3, 3a, 3b, 3c... Vertical transfer stage, 4... Horizontal transfer stage, 6, 12... Green filter, 7, 11... Red filter, 8, 13... Blue filter, 15... Vertical transfer section, 18... Solid-state image sensor. Figure 1 Figure 2 - Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10

Claims (1)

[Claims] 1. A color filter constructed by sequentially arranging color filter elements having three types of spectral characteristics so that their spatially modulated color signals are reversed by 180 degrees for each horizontal line, and a color filter consisting of identical color filter elements arranged vertically. A solid-state image sensor is configured by providing one vertical signal line in common for two light-receiving section rows, and the signals extracted from this solid-state image sensor are added between adjacent horizontal lines. A color solid-state imaging device characterized by obtaining a luminance signal.