JPS5856582A - Driving circuit for solid-state image pickup device - Google Patents

Abstract

PURPOSE:To prevent the generation of shading, by connecting one end of a current control element which is conducted when no horizontal transfer pulse exists to a power supply terminal of a current amplifying section supplying a drive pulse to a solid-state image pickup element and grounding the other end. CONSTITUTION:A driving pulse is inputted to an input terminal 12 and applied to an image pickup element such as CCD from an output terminal 13 after being current-amplified at a current amplification IC 11. A voltage from a power supply voltage line 14 is adjusted to a pulse voltage driven at the optimum state with a transistor (TR) 16 for current supply and a variable resistor 15, and applied to a power supply terminal 17 of the IC 11. A collector of a TR 22 for current uniforming is connected to the terminal 17 via a resistor 23 and the emitter is grounded. A pulse which is outputted only when no horizontal transfer pulse exists is applied to the base 24 of the TR 22. Thus, when flowing current to the IC 11 is decreased, a current from the TR 16 flows to ground via the resistor 23 to make the emitter current constant, allowing to prevent shading.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a driving circuit for a -dimensional or two-dimensional solid-state imaging device, and particularly to a driving circuit for a solid-state imaging device that prevents aging.

Conventionally, solid-state imaging devices produce images in the form of superimposed or modulated voltage fluctuation waveforms of the drive circuit caused by the difference in drive circuit current between when a drive signal is applied to the image sensor and when it is not. A phenomenon that appears in the output, that is, soning, was likely to occur.

Next, this soning will be specifically explained using a two-dimensional interline type image sensor as an example. 1st
The figure is a schematic diagram showing the principle of a two-dimensional interline type image sensor. This interline type image sensor basically consists of a light receiving section that converts optical information into an electrical signal and stores the electrical charge, and a section that transfers and reads out the electrical charge. In the figure, reference numeral 1 denotes a light receiving element arranged in a matrix. Charges accumulated in the light receiving element 1 are transferred to a charge coupled device (hereinafter referred to as COD) by controlling a transfer gate electrode 2 during a vertical graphing period. The signal is transferred to a vertical transfer unit 3 consisting of a CCD, and further transferred to a horizontal transfer unit 4 consisting of a CCD for each horizontal blanking. All of the charges transferred to the horizontal transfer section 4 are transferred to the leftmost output section 5 during the horizontal period and output as a video signal.

Here, assuming that the CCD is driven in two phases, these CODs are driven by each pulse signal shown in FIG. In FIG. 2, 6 is a vertical blanking pulse, 7 is a signal applied to the transfer case during the vertical blanking period, and 8 is a signal applied to the CCD 3 for vertical transfer. The period is one horizontal scanning period. Reference numeral 9 denotes a horizontal transfer/Prus, and 10 a cassette/Grus to be added to the output section 5.

FIG. 3 shows a pulse drive circuit, and the drive/Q pulse is as follows:
A signal from a signal generating circuit (not shown) is input to the input terminal 12 of the current amplifying circuit C11, and this ICI
After the current is amplified in step 1, it is applied to the image sensor from the output terminal 13. In the figure, the voltage from the power supply voltage line 14 is applied to a variable resistor 15 and a transistor 1 for supplying current.
6, the voltage is adjusted so that the image sensor can be driven in an optimal state.The voltage is applied to the power supply terminal 17 of the current amplifying ICII. In addition, 18
is a power supply/zoscon for AC components/9I/Yasu.

The -N pulse output from this drive circuit is applied to the image sensor, but since the image sensor is a so-called capacitive load such as a CCD, when the -P pulse is applied, fc'v C (however, fo is the clock frequency, ■ is the pulse voltage, and C is the load capacitance). For this reason, considering the voltage load capacity and frequency of each (drive/reset), the horizontal transfer/reset with the highest frequency
The circuit current of ZELS (usually more than 500 times that of other ZELS) is the highest, and the horizontal transfer ZELS with a larger load capacity has the highest circuit current. In order to transfer the signal charge from the vertical transfer section 3 to the horizontal transfer section 4 during the horizontal blanking period, the horizontal transfer/P pulse is
There is a break period for Gurus. Therefore, non-uniformity of drive current occurs in l horizontal periods. FIG. 4 shows the vertical transfer Psis 8, horizontal transfer Zolsu 9 (only one of the two phases is shown) for the horizontal blanking pulse 19, and the current waveform flowing from the power supply terminal 17 to the current amplification ICI 1. The phase relationship with 20 is shown. In order to suppress the voltage fluctuation of the power supply terminal 17 due to the change in the current flowing into the current increaser ICII (current waveform 20 in Fig. 4), the capacity of the power supply/guscon 18 should be increased appropriately, or The variation cannot be reduced unless the output resistance of the transoster 16 is made extremely small. This voltage fluctuation at the power supply terminal 17 affects the horizontal transfer signal and further affects the video output signal. In FIG. 4, 21 is
This is a waveform diagram showing the video output when the incident light to the image sensor is blocked, and the output should originally be horizontal in relation to the incident light, but due to the voltage fluctuation of the power supply terminal 17 mentioned above, the output is flat. There is no waveform and shading occurs.

This shading phenomenon is not limited to the above-mentioned interline type, but also frame transfer type and MO
This phenomenon occurs even in image pickup devices such as S type, which have to discontinuously use horizontal transfer and P pulses, which have a high frequency and a large circuit drive current, due to their operating principle.

The purpose of the present invention is to actively equalize the non-uniformity of the drive current in order to prevent the above-mentioned shading, and to prevent fluctuations in the power supply voltage of the water/P-transfer/P-rus circuit. An object of the present invention is to provide a driving circuit for a solid-state imaging device.

Next, a drive circuit according to the present invention will be explained based on an example. FIG. 5 is a circuit diagram showing an embodiment of the present invention, in which elements having the same functions as those in FIG. 3 are given the same reference numerals, and detailed explanation thereof will be omitted. Reference numeral 22 denotes a newly added current equalizing transistor, whose collector is connected to the power supply terminal 17 of the current amplifying ICII via a resistor 23, and whose emitter is grounded.

Then, the signal is output to the base 24 of the transoster 22 only during the period when the pulse 9 does not exist in the horizontal transfer shown in FIG. Pulse 25 is applied. Therefore, when the inflow current 26 to the current amplifying ICI I decreases, the current from the transistor 16 is caused to flow through the resistor 23 to the ground. At this time, by setting the resistor 23 to an appropriate value, the emitter current flowing through the transistor 16 becomes constant as shown by the solid line 26 in FIG.
The broken line is the case of the conventional example in which the transistor 22 is not added).

As a result, minute electronic fluctuations in horizontal transfer and signals are also prevented, and the video output signal 27 is improved from the conventional one shown by the broken line to the one shown by the solid line, and shading is prevented. Although this embodiment has been explained using an interline type image sensor as an example, the same applies to other solid-state image sensors that discontinuously use high-frequency phantom response. It is clear that it can be done.

As explained earlier, a transistor is added to the power supply terminal of the drive/resistance current amplifier section to prevent fluctuations in the power supply terminal voltage of the current amplifier section, so shading is prevented as much as possible, and the power supply/region The capacity of the scone can also be reduced,
Another effect is that the size of the imaging device can be reduced.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the structure of an interline image sensor, Fig. 2 is a waveform diagram of each part of the interline image sensor, and Fig. 3 is a drive circuit of a conventional solid-state image sensor. A block diagram, FIG. 4 is a waveform diagram showing the relationship between the current of the current increasing IC and the video output, and FIG. 5 is a block diagram showing an embodiment of the drive circuit of the solid-state imaging device of the present invention. FIG. 6 is a waveform diagram showing the relationship between the current of the current amplifying IC of the drive circuit shown in FIG. 5 and the video output. 11... Current amplification IC112... Input terminal, 13
...Output terminal, 14...Power line, 15...Variable resistor, 16 - Current supply transformer 2-star, 17...Power terminal, 18...PSco/, 19...Horizontal planking ξ Tsurus, 20... IC inflow current waveform for current amplification,
21...Image sensor output waveform, 22...Transistor,
23...Resistor, 25...Nollus waveform applied to the base of the Toranostar 22, 26...Inflow current waveform of the current amplification IC, 27...Image sensor output waveform.

Claims (2)

[Claims] (1) Make sure that one end of the current control element, which is turned on when no horizontal transfer pulse is present, is connected to the power supply terminal of the current amplification unit that supplies the drive signal to the solid-state image sensor, and the other end is grounded. Features a drive circuit for solid-state imaging devices. (2) A driving circuit for a solid-state imaging device according to claim (1), characterized in that a current amplifier is connected to a power terminal of the current amplifying section of the driving circuit. .