JPH0763093B2 - Driving method for charge transfer device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for driving a charge transfer element, and more particularly to a method for driving a charge transfer element suitable for reducing noise.

[Background of the Invention]

In recent years, charge transfer devices, especially CCDs (Charge Coupled Devices)
ce) is being applied in a wide range of fields such as signal processing such as analog delay and memory.

Conventionally, the diode cutoff method has been used as the input method of CCD signals. The potential balance method and the like are known.

For details of the prior art, see, for example, "Charge Transfer Device (CCD
BBD basics and applications) ”As described in Takeshi et al., Modern Science Co., Ltd. (February 1978), pp. 43-46, the potential balance method is used as a driving method for low noise. There is.

The low-frequency noise generated in the input section is a particular problem for the noise generated in the CCD, and it is necessary to reduce the input section capacitance in order to suppress it. However, in the conventional potential balance method, the amount of charge that can be transferred at this time is limited by the capacitance of the input section and the DC potential applied to the input gate, so the dynamic range is reduced. Also, when trying to increase the DC potential of the input gate to expand the dynamic range,
The drive potential of the transfer gate also has to be increased, which causes a problem of increased power consumption.

[Object of the Invention]

An object of the present invention is to provide a method for driving a charge transfer device, which solves the above-mentioned problems of the prior art, prevents the dynamic range in the CCD input section from being lowered, and enables reduction in miscellaneousness.

[Outline of Invention]

In order to achieve this object, the present invention transfers charges from the input diffusion layer, through the first input gate, and under the second input gate, to a potential difference between the first and second gates. A high-level pulse is applied to the second gate to increase the amount of charge during the period for storing the corresponding charge, and a low-level pulse is applied to the second gate during the period for transferring the charge from below the second gate to the transfer unit. Is characterized in that it is driven so as to transfer charges efficiently by applying the pulse.

Example of Invention

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

FIG. 1 is a sectional view of a CCD to which the present invention is applied, in which 1 is an N ⁺ diffusion layer of an input diode, 2 is a substrate, 3 and 3 ′ are input gates, 4 and 4 ′ are transfer gates, and 5 is It is a terminal.

FIG. 2 shows a CC when driven according to the first embodiment of the present invention.
FIG. 3 is a potential diagram of D, and FIG. 3 is a timing chart of drive pulses. The potential diagram of FIG. 2 shows the potential of electrons, the voltage V is directed downward in the drawing, 6,6 ′ represent the potential under each gate, 7,7 ′ represent the charge, and t ₁ , t ₂ , t
₃ corresponds to the pulse timings t ₁ , t ₂ and t ₃ in FIG. ₃ , respectively. The pulse timing in FIG. 3 is applied to each input terminal in FIG. 1, and 8 is an input signal.
The ID at time t ₁ is applied to the IG terminal to a low level, charges over the IG gate enters to IS gate. At this time, the IS pulse is set to high level to lower the potential and increase the amount of charge that can be transferred. The signal is applied to the IG gate to change the potential according to the signal voltage.

The time t ₂ the ID to a high level, accumulated under IS gate charge corresponding to a potential difference between IG and IS as the signal charges. Times of Day
t ₃ The low level of IS pulse, for transferring signal charges in H1 the H1 as a high level. In this way, as shown in FIG.
According to the H1 and H2 pulses, signal charges are sequentially transferred under the H1 and H2 gates.

In this embodiment, it will be explained below that even if the capacitance of the input gate IS is reduced, the dynamic range can be increased by applying a pulse to the IS gate as shown in FIG.

The potential of IG is ig, the potentials of IS at high level and low level are iS _h , iS _l , and the capacitance of IS is C, respectively. At this time, IS
The amount of charge Q that can be stored in Q is C = ig (i−iS _h ) ... (1), and by increasing the high level voltage of IS,
The electric charge Q can be increased by lowering the potential iS _h of IS. When this charge is transferred to H1, the IS potential must be higher than the potential of H1, but it can be easily transferred by setting the IS pulse to low level. In this way
The dynamic range can be expanded by pulse-driving IS.

Next, a second embodiment of the method of driving the charge transfer device according to the present invention will be described with reference to FIGS. In this embodiment, a CCD which is a horizontal register of the image pickup device is driven, and FIG. 4 shows the structure of the image pickup device.

In FIG. 4, 9 is a light receiving part, 10 is a CCD horizontal register, and 11 is an output part. FIG. 5 is a cross-sectional view taken along the line AA showing the structure of the portion a in FIG. 4, and has a structure similar to that shown in FIG. Further, FIG. 6 is a potential diagram when driving is performed according to this embodiment, and FIG. 7 is a timing chart of drive pulses.

In this embodiment, the transfer unit of the CCD is a three-phase drive of H1 to H3. Also, a DC voltage is applied to the IG gate to inject a constant bias charge, and the signal charge is directly applied to the light receiving unit 9 by CC
Transfer to D. The amount of charge to be injected is determined by the potential difference between IG and IS. At time t ₁ , ID is set to low level and IS is set to high level to lower the potential and increase the amount of charge. At time t _3, raising the potential IS as low, and transfers the H1. Thus, by driving the IS gate with a pulse, the dynamic range can be expanded as compared with the case where a DC voltage is applied.

〔The invention's effect〕

As described above, according to the present invention, even if the capacitance of the CCD input section is reduced to suppress low-frequency noise, driving can be performed without causing a decrease in the dynamic range, and the drawbacks of the above-mentioned conventional techniques are Except for this, it is possible to provide a driving method of a charge transfer device having an excellent function.

[Brief description of drawings]

1 is a sectional view of a CCD to which the present invention is applied, FIG. 2 is a potential diagram of the CCD when driven by the first embodiment of the present invention,
FIG. 3 is a timing chart of drive pulses, FIG. 4 is a configuration diagram of an image pickup device according to a second embodiment of the present invention, FIG. 5 is a sectional view taken along line AA in FIG. 4, and FIG. FIG. 7 is a potential diagram of the CCD when driven by the second embodiment of FIG. 7, and FIG. 7 is a timing chart of drive pulses. 1 ... N ⁺ diffusion layer, 2 ... substrate, 3,3 '... input gate, 4,4'
... Transfer gate, 5 ... Terminal, 6,6 '... Potential, 7,7' ... Charge,
8 ... Input signal, 9 ... Light receiving part, 10 ... Horizontal register, 11 ... Output part.

Claims (1)

[Claims] 1. A diffusion layer which supplies charges, a first input gate which is provided following the diffusion layer and whose potential is determined by the amount of charges to be transferred, and a first input gate which is provided subsequent to the first input gate, A second input gate to which a predetermined potential is applied, and a second input gate which is provided subsequent to the second input gate and transfers the charge accumulated by the potential difference between the first input gate and the second input gate. In a method of driving a charge transfer device having a transfer section, a high-level pulse is applied to the second input gate during a period in which charges from the diffusion layer are accumulated under the second input gate, During the period in which a low-level pulse is applied to the transfer unit adjacent to the second input gate and the charge accumulated under the second input gate is transferred to the transfer unit, the second input gate Low level It applies a pulse, the driving method of the charge transfer element and applying a pulse of high level to the transfer portion adjacent to the second input gate.