JPS61236277A - Image pickup device - Google Patents

Abstract

PURPOSE:To obtain an accurate black level by providing a clamping means which suppresses noises of a signal corresponding to the black level of each horizontal line and holding it, and fixes this level at the black level of a video signal. CONSTITUTION:Signal charges generated at an image pickup part PD according to the quantity of light with which a solid-state image pickup element 1 is irradiated are transferred by a synchronizing signal generating circuit 6 to a storage part SD in parallel and then transferred to a readout register RR to obtain a signal S1. Part of this signal S1 which is obtained in a blank read period and contains high frequency noises is noise-suppressed by a noise suppressing circuit 2 to obtain a signal S2. This signal S2 is sampled and held by an S/H 3 to obtain a signal S3 having a clock leak component removed. When a clamp pulse CP1 is inputted to a clamping circuit 4, the signal S3 in the entire horizontal blanking period is clamped to a new reference potential. Thus, a horizontal blanking signal level is fixed to the black level and a signal S4 obtained by reproducing a DC component is processed by a signal processing circuit 5 to obtain an NTSC signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an imaging device that obtains an accurate black level of a video signal.

[Prior art]

In general, video cameras that use an image pickup tube use a feedback clamp method, that is, a clamp circuit that clamps the level during the beam blanking period to a reference level as a black level, and a process that performs γ correction after amplifying this clamped signal. Considering a system consisting of a circuit, in order to stabilize the output of this system, the process circuit output is compared with a predetermined reference level, and a method can be considered to apply feedback to the clamp level so that the difference output becomes zero. ing. This method is possible with a camera using an image pickup tube.

However, when this method is used particularly in a solid-state imaging device, noise tends to enter the horizontal blanking period when attempting to secure a clamp period with a sufficient width for stable ramping.

In other words, in image pickup tubes, there is almost no noise mixed in during the blanking period, but in solid-state imaging devices, noise is generally large during the blanking period, and if normal clamping is performed during this period, the clamp level will fluctuate. ,
Also, while signal readout is stopped, it is normal to set the reference potential to a preset value, but since the reset potential fluctuates due to differences in the saturation resistance of the reset transistor and temperature characteristics, the blanking period remains unchanged during clamping. There was a problem in that it was not possible to use part or all of the signal.

〔the purpose〕

The present invention was made by focusing on such conventional problems, and it is possible to obtain an accurate black level. The purpose of the present invention is to provide an imaging device using a solid-state imaging device.

〔Example〕

A first embodiment of this invention will be explained using FIGS. 1 to 5.

In FIG. 1, 1 is a frame transfer type CCD (c
harge-coupled device ) (
As shown in FIG. 2, the imaging unit PD,
It is composed of a storage section SD, a readout register RR, an on-chip preamplifier AD, and a light shield @OS provided in the image pickup section FD. 2 is the signal S obtained from the CCD l during the blank read period OBI shown in FIG. 3(a).
1 (see FIG. 3(a)) in synchronization with the signal PN (see FIG. 3(b)). As shown in FIG. 4, the resistor 2a , 2b,
It is composed of a capacitor 2C, a transistor 2d, and a switching element 2e such as a switch. Reference numeral 3 denotes a sample and hold circuit (see FIG. 3(a)) from the noise suppression circuit 2 as a holding means for sampling and holding the signal S2 (see FIG. 3(a)) in synchronization with the signal PSH (see FIG. 3(c)).
Note that the noise suppression circuit 2 and S/H3 are
As shown in Figure 5.

Switches 2f, 2g, capacitors 2h, 2i, FET
2j and resistor 2, etc. may be configured in combination,
Reference numeral 4 denotes a clamp circuit (clamping means) for clamping the signal S3 from this S/H3, and as shown in FIG. 6, it is composed of an error amplifier 4a, a clamper 4b, a DC amplifier 4C, a sample and hold circuit 4d, capacitors C3 and C4, etc. has been done. 5 is a signal processing circuit that processes the output signal of this clamp circuit 4 to form an NTSC signal; 6 is a signal processing circuit that generates pulses for driving the CCD 1, noise suppression circuit 2, S/H 3, and clamp circuit 4; This is a synchronization signal generation circuit.

Next, the action will be explained.

For example, signal charges generated in the imaging unit PD during the l field period according to the amount of light irradiated to the CCD l are stored in the storage unit SD during the vertical blanking period by the synchronization signal generation circuit 6.
The signal charges of the storage unit SD are transferred in parallel to
Each horizontal row is transferred to the read register RR. Then, from the readout register RR, first, the signal of the light shielding part O8 is read out, then the image signal charge for one line of the image pickup part FD is read out, and furthermore, the blank readout signal obtained by driving the readout register RR is read out. P A M (pulse ampl 1t) as shown by the solid line in Fig. 3(a)
ude modulation) signal S1 is obtained.

In the signal Sl shown in FIG. 3(a), the OBI portion corresponds to the idle reading period, and the OH2 portion corresponds to the reading period from the light shielding portion O5.

Of the signals Sl, signals containing high frequency noise obtained during the idle reading period (the OBI portion shown in FIG. 3(a)) are suppressed by the noise suppression circuit 2 as described below. That is, when the pulse signal PN shown in FIG. 3(b) is input to the switching element 2e of the noise suppression circuit 2 and the switching element 2e is turned on, the signal input from the terminal A and obtained during the idle read period is teeth,
The signal is averaged with a time constant determined by the resistor 2a and the capacitor 2C, and is converted into a signal S2 having a waveform as shown in FIG. 3 (&).

Then, this signal S2 is processed by S/H3 as shown in Fig. 3 (C
), psua performs a sample and PSHb performs a hold operation in synchronization with the pulse signal PSH shown in ), signal S3, that is, the clock leak component as shown in FIG. 3(d) has been removed. Moreover, the level of most parts of the horizontal retrace period becomes a signal equal to the DC level of the signal S2. Now, the black level of OH2 in this signal S3 is sampled and held in the sample and hold circuit 4d in synchronization with the pulse CPoB, and this held voltage is applied to the error amplifier 4a.
Then, it is compared and amplified with the clamp reference voltage E, and is set as a new lamp reference potential.

This reference potential is held in capacitor C3. Therefore,
When the clamp pulse CPI shown in FIG. 3(f) is input to the clamper 4b, the signal S3 during most of the horizontal blanking period is clamped to this new reference potential. The video signal S4, whose horizontal blanking signal level is fixed to the black level by the clamp circuit 4 and whose DC component is reproduced, is processed by the signal processing circuit 5 and becomes an NTSC signal.

FIG. 7 is a block diagram showing a second embodiment of the invention.

In this second embodiment, a signal containing high frequency noise read out from the solid-state image sensor 1 and obtained during an empty readout period is first sampled and held by the S/H 7 to remove clock leak components, and then a clock leak component is removed. A noise suppression circuit 2 suppresses high frequency noise accompanying this sample and hold.

And by S/83 and clamp circuit 4.

The black level of the video signal input to the signal processing circuit 5 is fixed. In this way, the level of the signal S2 during the period OBI can be made almost equal to the level of the DC component of the signal obtained during the period OB2, which has the effect of narrowing the dynamic range of the clamp circuit 4.

In addition, the number of pixels of the light shielding part O8 of the solid-state image sensor l is increased,
The clamped signal may be obtained only from the signal OB2 corresponding to the light shielding part O5 without performing blank reading on the front porch during the horizontal blanking period. In this case, the signal for the black level of 082 is first obtained. The included high frequency noise is suppressed by the noise suppression circuit 2, and then the signal obtained from the noise suppression circuit 2 is passed to the clamp circuit 5.
This causes the lamp to be clamped to the new lamp reference potential. Even in this case, the same effects as in the first embodiment can be achieved.

Furthermore, it goes without saying that the light shielding section O3 may be provided at the right end of the imaging section FD, and a signal may be obtained from the light shielding section O3 during the period OBI.

〔effect〕

As described above, the present invention has the advantage that stable lamp operation can be performed, so that accurate black level can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention, FIG. 2 is an explanatory diagram of the COD used in this embodiment, FIG. 3 is a waveform diagram of each part shown in FIG. 1, and FIG. 5 is a diagram showing a specific example of the noise suppression circuit 2, FIG. 6 is a block diagram showing an example of the configuration of the clamp circuit 4, and FIG. 7 is a block diagram showing a second embodiment of the present invention. 2... Noise suppression circuit (noise suppression means) 3.
...Sample hold circuit (holding means) 4...
...Clamp circuit (clamping means) Fig. 7 Fig. 2

Claims (1)

[Claims] Noise suppressing means for suppressing noise in a signal corresponding to the black level of each horizontal line signal from the solid-state image sensor; holding means for holding this noise-suppressed signal; An imaging device comprising: clamping means for fixing to a level.