JPS5979688A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To remove synchronous noise in a video band in accordance with the elapse of time by storing the synchronous noise unrelated to the quantity of incieent light and subtracting the stored value from a signal outputted from the effective picture part of a solid-state image pickup element. CONSTITUTION:The output video signal from the solid-state image pickup element 13 is amplified to a prescribed level, converted into a digital signal by an A/D converting circuit 64 and stored in a storage circuit 65. The storage circuit 65 is controlled by a control circuit 66 and stores an output signal corresponding to a part shielded by the element 13. A synchronous noise stored in the storage circuit 65 is read out by an output from the control circuit 66, converted into an analog signal and supplied to a subtracting circuit 68. The circuit 68 subtracts the synchronous noise from an output video signal from the element 13 and outputs a video signal free from the synchronous noise.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a CCD (Charge Coup
The present invention relates to a solid-state imaging device using a solid-state imaging device such as lsdDsvlcs).

[Technical background of the invention and its problems]

As is well known, it takes several V to I to drive a solid-state image sensor.
A clock signal having a peak value around OV is used. The frequency of the clock pulse signal in devices currently in practical use is approximately 14 MHz, and this clock pulse signal is used for two to four phases. In addition, to drive the solid-state image sensor, there are seven readout stages in addition to the clock and pulse signals mentioned above.) A? Pulse signals such as pulse signals and sample-hole pulse signals are also used.

In this way, various pulse signals are required to drive the solid-state image sensor.

Incidentally, the wiring between the solid-state image sensor and the various A' signal systems may be close to each other. Therefore, due to the influence of stray capacitance between lines, etc., the clock pulse signal and the like may be mixed as synchronous noise into the output signal (video signal according to the amount of incident light) of the solid-state image sensor. This noise is not constant for each imaging element or imaging device due to differences in stray capacitance, inductance, and ground potential between lines. Furthermore, since the factors contributing to this noise change depending on the surrounding environmental conditions and changes over time, there are many difficulties in designing and manufacturing to keep this synchronous noise stable and at an extremely low level. Moreover, even if the clock/malus signal is outside the video frequency band, this synchronous noise uses 2- to 4-phase pulses or other signal signals, so the difference in the induced level from each phase pulse etc. It appears as a video band component due to this. Therefore, although synchronous noise outside the video band can be removed by a low-pass filter, it has been difficult to remove synchronous noise within the video band without deteriorating the frequency characteristics within the video band.

[Purpose of the invention]

This invention was made based on the above circumstances, and its purpose is to eliminate synchronous noise in the video band in response to changes over time, and to obtain a high-quality video signal. The present invention aims to provide an imaging device.

[Overview of the invention]

The present invention shields at least one horizontal line of a solid-state image sensor, stores the output signal of this shielded portion, that is, synchronous noise that is not caused by the amount of incident light, and combines the stored synchronous noise with the effective screen of the solid-state image sensor. Synchronous noise within the video band is removed by subtracting the signal output from the video band.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, an image of a subject 11 is formed on a solid-state image sensor 13 via a lens optical system 12.

FIG. 2 shows this solid-state image sensor 13, and 21
is the light receiving part. Light receiving elements (not shown) for photoelectrically converting incident light are arranged in this light receiving section 21, and the portion located below this light receiving section 21 (upper side on the screen because the subject is an inverted image) For example, light shielding members 23 and 24 are provided to cover the light receiving elements for one horizontal line and the readout portion 22 for reading out the video signal components distributed on the horizontal line on the time axis. Further, 25 is an output terminal provided in the readout portion 22.

As is well known, the output signal of the solid-state image sensor has a waveform in which the read clock pulse signal is amplitude-modulated according to the amount of incident light. FIG. 3 shows the output signal of the portion covered by the light shielding members 23 and 24 of FIG. 2. Since this portion is shielded from incident light, only the read clock pulse signal of the solid-state image sensor 13 is output (strictly speaking, it is a clock pulse signal and a dark output voltage). When the output signal of this part is enlarged for part A, it becomes as shown in FIG. That is, the peak values of the read clock pulse signal are different for each phase of the clock pulse signal. This is synchronous noise for the reasons mentioned above. Therefore, the waveform of one horizontal line output (synchronous noise en(t)) of the shielded portion is not flat, as shown in FIG. 5(,l). In the case of the interline solid-state image sensor 13, this synchronous noise e n (t) is uniform over the entire screen, so it is included in the video signal output from the light receiving section 21 other than the shielded portion. Also included. That is, if the amount of incident light on one horizontal line of the light receiving section 2 is as shown in FIG. 5(b), the ideal output signal waveform en(
t) is also similar to FIG. 5(b). However, in reality, the synchronous noise en(t) is superimposed on the output signal waveform e(t), resulting in a waveform as shown in FIG. 5(c).

Next, an apparatus of the present invention using the solid-state image sensor 13 having the above configuration will be described.

In FIG. 6, reference numeral 13 denotes an interline solid-state imaging device similar to that in FIG. 2, and this solid-state imaging device 13 is driven by a plurality of clock pulse signals generated by a drive circuit 6.

This drive circuit 61 is supplied with horizontal and vertical drive/volume pulse signals SHP + svp. A signal etc. is generated.

The output video signal of the solid-state image sensor 13 operated by this clock pulse signal etc. is supplied to an amplifier circuit 62 and amplified to a predetermined level. The output signal of this amplifier circuit 62 is supplied to a delay circuit 63 and an AJ''D (analog/digital) converter 64. This converter 64 receives the output signal of the amplifier circuit 62 from the drive circuit 61. The signal for one horizontal line is converted in synchronization with each clock pulse signal, and the output signal of this ψ converter 64 is stored in a storage circuit 65. It is controlled by a control circuit 66 that generates write and read signals in synchronization with the shielding signals SHP and svp, and stores output signals corresponding to the shielded portions of the solid-state image sensor 13.
For example, if the converter 64 has an 8-bit configuration, 8
A bit output signal is stored every clock.

By the way, the number of output lines from which images can be taken out of the solid-state image sensor 13 is determined by the number of horizontal lines. This number is designed to be greater than the number of lines in an l frame specified by the scanning method minus the number of horizontal lines in the entire vertical blanking period, and the blanking of the final mixed system allows Solid-state image sensor 13
This is to prevent blanking portions from occurring due to an insufficient number of lines. That is, in FIG. 7, 71 is the phase of the trailing edge of the system vertical blanking, and 72.73
．． 74.75 is the output video signal of the solid-state image sensor 13 whose phase is advanced by υ. Of these, 72.73 is the output signal of the light shielding part, that is, the synchronous noise en(t
). Therefore, in the example shown in FIG.
A line portion of 2.73 is written into the memory circuit 65 under the control of the control circuit 66.

On the other hand, after 74 shown in FIG. 7, the control circuit 66 causes the storage circuit 65 to perform a read operation for each horizontal line, and the stored synchronous noise an(t) is read out and D/11. (Diphthal/analog) converter 67
supplied to In this D/A converter 67, synchronous noise e
n(t) is converted into an analog signal, and this converted signal is supplied to a subtracter 68 together with the video signal whose phase has been horizontally aligned by the delay circuit 63. As mentioned above, the output video signal of the solid-state image sensor 13 is composed of the signal component e(t) and the synchronous noise en(
The sum of t) is e(t) + en(t) (1). In the subtracter 68, e(t) + en(t) - en(t) = e(t
) ...... (2) is performed, and the above (
1) According to equation 1, the synchronous noise e n (t) is subtracted. Therefore, this subtracter 68 outputs synchronous noise e n(t
) is removed and only the video signal is output.

According to the above embodiment, one horizontal line and the readout portion of the solid-state image sensor 13 are covered by the light shielding members 23 and 24, and the output signal of this light shielding portion, that is, the synchronous noise caused by the amount of incident light is stored. Synchronous noise within the video band is removed by subtracting the stored synchronous noise and the signal output from the effective screen area of the solid-state image sensor.

Therefore, even if the synchronous noise changes over time, the noise can be reliably removed and a high quality video signal can be obtained.

Note that this invention is not limited to the above embodiments,
For example, the output signal of the amplifier circuit 62 is A/'D converted and then supplied to the delay circuit 63 and the memory circuit 65, and the output signal of the delay circuit 63 and the synchronous noise read out from the memory circuit 65 are digitally converted. It may also be configured to perform subtraction and then convert into an analog signal. In this case, the delay circuit 63 is digital.

In addition, in the amplifier circuit 62, a portion of the output video signal of the solid-state image sensor 13 that does not depend on the amount of incident light of the pulse amplitude modulated wave, that is, an output signal component due to the clock pulse signal, is cut out to some extent or most of it by a slice circuit. After that, it is also possible to perform subsequent processing.

Furthermore, the delay circuit 63 may be provided between the VA converter 67 and the subtracter 68.

Although the above embodiments have been described with reference to a case in which a single solid-state image sensor is used, the present invention can also be applied to a case where a plurality of solid-state image sensors are used, such as in a color television camera. In this case, A
The /D converter 64 may be provided corresponding to the solid-state image sensor of each primary color, or the output signal of each primary color may be time-divided and supplied to the A/D converter 64.

Further, writing of synchronous noise into the memory circuit 65 may be performed only when the solid-state imaging device 13 is powered on, but by constantly operating, noise can be stably removed against drift during operation.

Furthermore, although the above explanation has been made regarding an interline type solid-state image sensor, the present invention can be applied to any solid-state image sensor that generates synchronous noise with a uniform phase over the entire screen. is possible.

It goes without saying that various other modifications can be made without departing from the gist of the invention.

〔Effect of the invention〕

As detailed above, according to the present invention, it is possible to remove synchronous noise in the video band in response to changes over time.
A solid-state imaging device capable of obtaining high-quality video signals can be provided.

[Brief explanation of the drawing]

The drawings are for explaining the present invention, and FIG. 1 is a diagram showing the relationship between a subject, an optical system, and a solid-state image sensor, FIG. 2 is a diagram showing the configuration of a solid-state image sensor applied to this invention, and FIG. 4 and 5 (a), (b), and (c) are diagrams shown to explain the output signals of the solid-state imaging device shown in FIG. 2, respectively, and FIG. 6 is a solid-state imaging device according to the present invention. FIG. 7 is a block diagram showing one embodiment of the present invention, and FIG. 7 is a diagram shown to explain the operation of FIG. 6. 13... Solid-state image sensor, 61... Drive circuit, 63...
...Delay circuit, 64...A/D converter, 65...Storage circuit, 67...D/A converter, 68...Subtractor. Applicant's agent Patent attorney Takehiko Suzue 3 Figure 5 Figure 6 1'-1 SHP SVP Figure 7

Claims (1)

[Claims] a solid-state image sensor in which at least one horizontal line is shaded;
A drive circuit drives the solid-state image sensor in synchronization with the horizontal and vertical drive pulse signals, and a drive circuit that drives the output signal of the solid-state image sensor in synchronization with the horizontal and vertical drive pulse signals. 1. A solid-state imaging device, comprising: storage means; and means for subtracting the stored signal from a signal output from the solid-state imaging device.