JPH02230747A - Charge-coupled device and driving method therefor - Google Patents

Abstract

PURPOSE:To obtain a good output waveform by a method wherein a capacitor is inserted in the signal route of an amplifier provided on the rear step of a floating diffused layer and the potential on the side of the output terminal of this capacitor is reset in a reference potential. CONSTITUTION:A capacitor 23 is connected between an output terminal of a first source follower circuit and an input terminal of a second source follower circuit. Moreover, a drain is connected to a reference potential VCC at the connection point of the capacitor 23 with the second source follower circuit and a source of a MOS transistor 23, to which a second reset pulse phiR2 is applied, is connected to a gate. In case the amount of a signal charge is a large quantity or in case the signal charge is transferred at high speed, the potential of the input terminal of the second source follower circuit is reset in the reference potential every constant period even if the potential of a floating diffused layer can be reset only incompletely. Thereby, the output waveform of an output terminal VOUT becomes a good one.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a charge-coupled device, and particularly to a charge-coupled device for obtaining a good output even when the floating diffusion layer is incompletely reset, especially when operating on a low-voltage power supply. This invention relates to a charge-coupled device having a circuit and a method for driving the same. [Prior Art] Conventionally, a charge coupled device shown in FIG. 5(a) is known as a charge coupled device having an output mechanism that can operate even with a low voltage power source. In the same figure, on the P-type semiconductor substrate 1,
An N-type transfer channel, a floating diffusion layer 3, a transfer region 5a, and a drain diffusion layer 4 are formed on the semiconductor substrate, and gate electrodes 10 to 17 are formed on the semiconductor substrate via an insulating film 2.
is formed. Further, P-type diffusion layers 6 to 9 are formed in the transfer channel 5 and the transfer region 5a to form a potential barrier. A two-stage source-flow lower circuit composed of MOS transistors 18 to 21 is connected to the floating diffusion layer 3. Next, the operation of the apparatus shown in FIG. 5(a) will be explained with reference to FIGS. 5(b) to 5(d) and FIG. 6(a). Figures 5(b), (c), and (d) show the sixth
FIG. 5 is a potential diagram in the cross section of FIG. 5(a) at timings 1, 12, and t3 shown in FIG. 5(a). As shown in FIG. 5(b), when 1=1, the transfer pulse φ1 is at a low level, the transfer pulse φ2 is at a high level, and the first reset pulse φR1 is at a low level, so that the potential under the gate electrode 13 is The signal charge Q accumulated in the well is transferred into the floating diffusion layer 3 through under the output gate electrode 14 to which the DC voltage V00 is applied. Here, the signal charge Q is converted into a voltage signal V 51G by the floating capacitance cpo of the floating diffusion layer 3, and is converted into a voltage signal V 51G by the MOS transistors 18 to 51G connected between the DC power supply VDD and the ground potential.
The impedance is converted by the source follower circuit consisting of 21 and output terminal ■. Retrieved from LIT. At t-t2, φl is at a high level, φ2 is at a low level, and φRl is at a high level, and the signal charge Q in the floating diffusion layer 3 passes under the gate electrode 15 into the potential well formed under the gate electrode 16. will be forwarded to. At this time, the potential in the floating diffusion layer 3 is reset to the potential below the gate electrode 15. Furthermore, when 1=1, φR1 becomes a low level, and the signal charge Q accumulated in the potential well under the gate electrode 16 passes under the gate electrode 17 to which the DC voltage VR is applied, and resets the DC voltage. Drain voltage ■R
It is discharged to the drain diffusion layer 4 to which D is applied. In this way, in the conventional example, the floating diffusion layer is reset to a potential deeper than the potential of the reset pulse φ, by taking advantage of the fact that an internal potential deeper than the gate voltage is formed in the buried channel. , a large dynamic range can be obtained even when the reset drain voltage VRD is low. [Problems to be Solved by the Invention] In the above-described conventional charge transfer device, when resetting the potential of the floating diffusion layer 3, the floating diffusion layer 3 is not depleted, so the charge transfer is performed by the bucket brigade. device·
mode, and when the signal charge is large or the transfer is high speed, it cannot be completely reset, and a portion of the charge ΔQ remains as shown in FIG. 5(d). in this case,
The potential of the floating diffusion layer 3 is reduced by the potential ΔVSIG corresponding to the residual charge amount ΔQ, and becomes lower than the normal reset level by Δ■sIo, as shown in FIG. 6(b).

Therefore, when the floating diffusion layer 3 subsequently receives a signal charge, the voltage value will be lower by ΔVSIa than the voltage value that should originally be output, so when the charge shown in FIG. 7(a) is transferred to the floating diffusion layer 3, , the output voltage of the output terminal vout is as shown in FIG. 7(b). When this output voltage is processed using a sample and hold circuit, the result is shown in Figure 7 (C).
A waveform shown in is obtained, but this waveform is deviated from the waveform that should originally be output (see FIG. 3(c)).

[Means for Solving the Problems] The charge-coupled device of the present invention includes a charge transfer region, a transfer electrode provided on the charge transfer region, and a floating diffusion layer provided at the final stage of the charge transfer region. , a rectangular reset mechanism for resetting the potential of the floating diffusion layer at regular intervals, and an amplifier circuit connected to the floating diffusion layer and having an output terminal, the amplifier circuit including the floating diffusion layer. A capacitor having a first terminal connected to the diffusion layer side and a second terminal connected to the output terminal side is inserted, and the second terminal of the capacitor is connected to a constant potential at a constant period. A reset circuit is connected to reset the

Further, in the driving method, the resetting of the potential of the second terminal of the capacitor by the reset circuit is such that after the potential of the floating diffusion layer is reset by the reset mechanism, the next signal charge is applied to the floating diffusion layer. This is done before the charge is transferred from the charge transfer region.

[Example] Next, an example of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view and a circuit diagram showing one embodiment of the present invention, and the same parts as in the conventional example shown in FIG. Explanation will be omitted. The difference between this embodiment and the conventional example is that a capacitor 23 is connected between the output terminal of the first source follower circuit and the input terminal of the second source follower circuit; At the connection point with V, the train is at the reference potential V. 0 and the source of the MOS transistor 23 to which the second reset pulse φa2 is applied is connected.

Next, the operation of the apparatus of this embodiment will be explained with reference to FIGS. 2 and 3. In this device, the transfer pulses φ1, φ2 and the first reset pulse φ8 shown in FIG.
The potential states at times 1, t2, and t3 when , are applied are the same as those of the conventional example shown in FIGS. At time t2, a second reset pulse φR2? is applied to the gate electrode of the MOS transistor 22. Therefore, the potential of the capacitor 23 is equal to the reference potential VCC.
As a result, the output voltage at the output terminal VOUT can return to the standard level as shown in FIG. 2(b).

At this timing, the second reset pulse φ8■
By setting to high level, the output waveform diagram of each part is as follows.
The results are as shown in FIGS. 3(a) to (c). That is, the input waveform at the input terminal VIN of the first source-flat lower circuit is shown in FIG. Therefore, the output waveform of the output terminal vOUT becomes as shown in FIG. 3(b), and when this output is passed through a sample and hold circuit, a signal having the waveform as shown in FIG. 3(c) is obtained.

As explained above, in this embodiment, in a charge-coupled device that can operate at a low power supply voltage, when a large amount of signal charge is transferred or when transferring at high speed, the potential of the floating diffusion layer is set in an incomplete manner. Even if this is not possible, a good output waveform can be obtained by inserting a capacitor in the signal path of the amplifier provided after the floating diffusion layer and resetting the potential on the output terminal side of this capacitor to the reference potential.

Next, another embodiment of the present invention will be described with reference to FIGS. 4(a) and 4(b). FIG. 4(a) is a time chart showing the pulse waveform of the driving pulse in this embodiment, and FIG. 4(b) is an output waveform diagram when driving using this driving pulse.

In this embodiment, after the first reset pulse φR1 becomes low level, the second reset pulse φR2 is set to high level. In this way, the signal component △V! due to the residual charge △Q! In addition to being able to compensate for JIG, it is also possible to remove the distribution noise component when φRl becomes low level.

[Effects of the Invention] As explained above, the present invention provides a charge transfer device having an output a-shaped using a floating diffusion layer and capable of operating at a low power supply voltage, in which an amplifier that is not provided after the floating diffusion layer is used. A capacitor is inserted in the signal path of , and a reset circuit is connected to the output terminal of this capacitor, so the potential of the output terminal of this capacitor can be changed after resetting the potential of the floating diffusion layer. Before the next signal charge is transferred to this diffusion layer, it is reset to the reference potential, so according to the present invention, when the amount of signal charge is large or when the driving speed is high, Even if the potential of the floating diffusion layer cannot be completely reset, an accurate signal waveform can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view and a circuit diagram showing an embodiment of the present invention, and FIGS. Figure 3 (a
冫～(c) is an explanatory diagram of the operation of the device in FIG. 1, FIG. 4(a)
) and (b) are drive pulse waveform diagrams showing other embodiments of the present invention and output waveform diagrams when the drive pulses are used, respectively, and FIG. 5(a) is a cross-sectional diagram and circuit diagram of the conventional example. figure,
Figures 5(b) to (d) are potential diagrams for the cross section shown in Figure 5(a), and Figures 6(a) and (b) are respectively for the device shown in Figure 5(a). The drive pulse waveform diagram and its output waveform diagram, FIGS. 7(a) to (C), are explanatory diagrams of the operation of the conventional example. 1... P-type semiconductor substrate, 2... Insulating film, 3...
・Floating diffusion layer, 4...Drain diffusion layer, 5...
Transfer channel, 5a...Transfer area, 6~
9...P-type diffusion layer, 10-17...gate electrode, 18-22...MoS transistor, 23...
・Capacitor.

Claims (2)

[Claims] (1) A charge transfer region, a transfer electrode provided on the charge transfer region, a floating diffusion layer provided at the final stage of the charge transfer region, and the potential of the floating diffusion layer are reset at regular intervals. and an amplifier circuit connected to the floating diffusion layer and having an output terminal, the amplifier circuit has a first terminal connected to the floating diffusion layer side and the output terminal side A capacitor having a second terminal connected to the capacitor is inserted, and a reset circuit for resetting the terminal to a constant potential at regular intervals is connected to the second terminal of the capacitor. charge-coupled device. (2) A charge transfer region, a transfer electrode provided on the charge transfer region, a floating diffusion layer provided at the final stage of the charge transfer region, and resetting the potential of the floating diffusion layer at regular intervals. an amplifier circuit connected to the floating diffusion layer and having an output terminal; a first terminal connected to the floating diffusion layer side and a second terminal connected to the output terminal side; A method for driving a charge-coupled device comprising: a second terminal of the capacitor; and a reset circuit connected to a second terminal of the capacitor and resetting the terminal to a constant potential at regular intervals, The potential of the second terminal is reset after the potential of the floating diffusion layer is reset by the reset mechanism and before the next signal charge is transferred from the charge transfer region to the floating diffusion layer. A method for driving a charge-coupled device characterized by: