Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Charge transfer device
Reexamination Certificate
1997-01-27
2001-10-30
Ngô ;, Ngâ ;n V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Charge transfer device
C257S240000, C257S315000
Reexamination Certificate
active
06310369
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a charge-to-voltage converter for converting signal charge packets transferred thereto from a charge transfer region into a signal voltage. In particular, it relates to a charge-to-voltage converter of a floating diffusion output type and a floating gate output type.
In a horizontal charge transfer region of a CCD area sensor or in a charge transfer region of a CCD delay line, a charge-to-voltage converter of a floating diffusion output type or a floating gate output type is employed as an output circuit for detecting input signal charge packets obtained from a charge transfer region and converting such signal charge packets into a signal voltage.
As shown in
FIG. 5
, in a conventional charge-to-voltage converter of a floating diffusion output type, a positive pulse is applied to a precharge gate
7
to switch on the PG
7
, so that a potential in an floating diffusion (FD) region
1
can be used as a precharge voltage Vpd applied to a precharge drain (PD) region
2
. Subsequently,in a state where the precharge gate is switched off, the signal charge packets transferred from a CCD transfer region
3
are injected into the FD region
1
via an output gate (OG). A signal voltage is produced by detecting the signal potential variation caused in the FD region
1
.
Meanwhile as shown in
FIG. 6
, in another conventional charge-to-voltage converter of a floating gate output type, an floating gate (FG)
4
is provided on a substrate and is partially overlapped by output gate (OG) of a CCD transfer register
3
, and the switching (on/off) action of a MOS transistor
5
is controlled by reset clock pulses &phgr; reset of a predetermined period, so that the FG
4
can be reset periodically to a reset voltage Vreset. A signal voltage is obtained by utilizing the potential variation caused in the FG
4
in accordance with the signal charge passed through the channel under the FG
4
.
However, in the conventional charge-to-voltage converter of a floating diffusion output type and a floating gate output type mentioned above, the capacitance of the converter is of a fixed value. It is, therefore, impossible to selectively change the charge-to-voltage conversion factor of the converter, and the conversion factor is determined merely as a single value as follows.
With regard to the signal charge quantity Q, the signal amplitude V in the FD region
1
(in
FIG. 5
) and
11
(in
FIG. 6
) is expressed as
V=Q/C=Ne−/C (1)
where N is the number of electrons; e-denotes an elemental charge (−1.6×10−19[C]); and C is the capacitance of the FD region
1
(in
FIG. 5
) and
11
(in FIG.
6
).
Therefore the conversion factor &eegr;H, i.e., the signal amplitude obtained at the time of input of one electron to the FD region
1
(in
FIG. 5
) and
11
(in FIG.
6
), is given by
&eegr;H=V/N=e−/C (2)
As a result, if the conversion factor is once set to a great value in design, the amplitude of the converted voltage is rendered excessively high when a large quantity of signal charge packets is input. Consequently such amplitude exceeds the maximum allowable limit of the converter to eventually raise a problem that proper charge-to-voltage conversion fails to be executed, whereby a sufficient dynamic range of conversion is not achievable.
To the contrary, if the conversion factor of the converter is set to a small value in design for the purpose of complying with a large quantity of input signal charge packets as well, the amplitude of the converted voltage is rendered excessively low when the input signal charge packets are small in quantity. Harmful influence of noise is prone to be induced by the excessively low voltage which eventually raises a problem in practical use. In this case also, therefore, a sufficient dynamic range of conversion is not achievable either.
SUMMARY OF THE INVENTION
In view of the circumstances mentioned, it is an object of the present invention to provide an improved charge-to-voltage converter which is changeable of the charge-to-voltage conversion factor of the converter by changing the capacitance of the floating diffusion or floating gate.
It is another object of the present invention to provide an improved charge-to-voltage converter which is capable of realizing a sufficiently wide dynamic range in the conversion to comply with any state where the input signal charge packets are extremely small or great in quantity.
In one aspect of the present invention, there is provided a charge-to-voltage converter of a floating diffusion output type for producing a signal voltage by injecting signal charge packets transferred from a charge transfer region into a floating diffusion region via an output gate. The converter includes a precharge drain region which is supplied with a reset voltage, a diffusion region which is formed between the floating diffusion through a first channel region and the precharge drain region through a second channel region, a first precharge gate electrode which is formed on the first channel region and a second precharge gate electrode which is formed on the second channel region.
In another aspect of the present invention, there is provided a charge-to-voltage converter of a floating gate output type for producing a signal voltage out of signal charge packets transferred thereto from a charge transfer region by detecting a potential variation in a floating gate provided on a substrate and is partially overlapped by output gate electrode of the charge transfer register. The converter includes a first diffusion region which is supplied with a reset voltage, a plurality of diffusion regions which are formed between the floating gate and the first diffusion region through a first channel region, at least one channel region which are formed between the diffusion regions and a plurality of reset gate electrodes which are formed on the first channel region and the at least one channel region.
In accordance with the present invention, since the capacitance of the floating diffusion or floating gate is changeable, hence achieving advantageous effects that the dynamic range of conversion can be widened. Therefore, when the invention is applied to a CCD imager or the like, a remarkable compliance is attainable in any state where the quantity of input light is extremely small or great.
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Maki Yasuhito
Narabu Tadakuni
Sato Maki
Ngô ; Ngâ ;n V.
Sonnenschein Nath & Rosenthal
Sony Corporation
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