Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1998-01-08
2001-06-12
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S2140RC
Reexamination Certificate
active
06246042
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to digital imaging devices and more particularly to digital pixel configuration.
2. Description of Related Art
Imaging sensing devices are the light detecting component in digital imaging systems, such as for example, digital cameras. An image sensing device, such as a camera, uses light to capture an image by a semiconductor-based chip. The chip replaces film in traditional film-based systems. In a camera, an image sensing device is configured, in its simplest form, to capture a monochrome or color image by way of semiconductor devices such as transistors, capacitors, and photodiodes. In one example, the image sensing device is a chip made up of a number of pixels, each pixel capable of absorbing light. In color applications, each pixel generally absorbs light through a filter and represents one color corresponding to the image sensed.
In general, a pixel contains a photosensing structure, such as a photodiode, and other pixel circuitry. The photosensing structure is the region of the pixel that responds to light. For example, a pixel circuit having a photodiode is charged to, for example, 5 volts. The photodiode is exposed to light and the pixel circuit discharges its stored energy depending on the intensity of the light exposure.
FIG. 1
illustrates an example of a prior art pixel circuit
10
described in U.S. Pat. No. 5,471,515. Prior art pixel circuit
10
contains a photosensing structure
20
, such as for example, a photodiode that is sensitive to light. The circuit also contains a SAMPLE capacitor
70
. SAMPLE capacitor
70
is initially charged to, for example, 5 volts by connecting the circuit to V
CCT
50
which is the source connection of transistor M
1
through transistor M
2
. Pixel circuit
10
also includes a RESET signal
30
that is coupled to the gate of transistor M
1
that charges diode
20
when desired. Pixel circuit
10
contains a SAMPLE signal
40
coupled to the gate of transistor M
2
. SAMPLE signal
40
regulates the amount of time that photodiode
20
is permitted to be exposed. In other words, SAMPLE signal
40
regulates the discharge time of capacitor
70
according to, for example, the light exposure. Pixel circuit
10
further contains a driver, represented by transistor M
3
, which receives power from V
CC
60
to take the signal from pixel circuit
10
and drive it off the chip to other process circuitry. Transistor M
4
selects when transistor M
3
drives bitline signal
90
which signals pixel
10
.
A digital imaging device is made up of a plurality of pixels. One problem in using a plurality of semiconductor devices to make the individual pixels is that each of the pixels across the chip can differ. This is particularly seen in the amount of underlying leakage occasioned by the circuitry associated with charging and storing the individual capacitors associated with each pixel circuit. The leakage problem is addressed by compensating for the leakage on a pixel by pixel basis. This is done by conducting a dark picture operation wherein capacitor
70
is charged by V
CCT
50
through transistors M
1
and M
2
. Transistor M
2
is turned off and the dark-picture reference signal in capacitor
70
is driven out. Through this operation, the device can compensate for individual leakage by each pixel by evaluating each pixel individually. Thus, the steps to, for example, take a picture include taking a picture of the desired image and then taking a dark-picture to calibrate the individual pixels.
FIG. 2
illustrates a schematic layout of a pixel array
100
for a digital imaging device, such as for example, a digital camera.
FIG. 2
shows six pixels
110
, each pixel being substantially square in shape and having individual pixel circuitry
10
, such as the circuitry described in FIG.
1
.
FIG. 2
also shows pixel circuitry
10
coupled to photosensing structure
20
, such as for example, photodiode
20
in FIG.
1
. As shown in
FIG. 2
, the individual pixels
110
that make up the pixel array
100
are formed substantially identically or replicated throughout pixel array
100
.
In digital imaging devices, the portion of the pixel that absorbs light is very important because that portion comprehends or interprets the amount of light that hits the pixel. Thus, the larger the photosensing structure, such as a photodiode, is, the better the interpretation or comprehension of the light that hits the pixel.
Prior art structures are limited in the size of the photosensing structure by the amount of additional circuitry needed to operate the chip, such as pixel circuitry
10
. Thus,
FIG. 2
illustrates the typical configuration of a substantially square pixel having a photosensing structure
20
that consumes about 50 percent of pixel
110
surface area. The other 50 percent of pixel
110
cannot interpret any light that strikes that portion of the pixel.
Photosensing structure
20
is typically formed in the chip substrate. For a semiconductor substrate, such as a silicon substrate, a photosensing structure that is a photodiode is formed commonly in the chip via a P-N junction. The additional circuitry
10
is formed of transistors and contacts to the individual transistors. Thus, the contacts require conductive, generally metal, layers to the devices. These contacts are generally formed of aluminum or an aluminum alloy in a manner similar to other integrated circuit chips by the deposition of multiple conductive layers each separately insulated from one another by a layer of dielectric material.
SUMMARY OF THE INVENTION
A pixel array is disclosed. The pixel array includes a first pixel having side portions and a first pixel layout. The pixel array also includes a second pixel adjacent to the first pixel, the second pixel having a second pixel layout configured to substantially mirror the first pixel layout about one of the side portions of the first pixel.
In a further aspect of the invention, a method of forming a pixel array is disclosed. The method includes providing a semiconductor substrate having a first pixel area and a second pixel area adjacent the first pixel area, forming a photosensing structure in the first pixel area and a second photosensing structure in the second pixel area, and forming a pixel operating circuit in a portion of the first pixel area and in a portion of the second pixel area, the pixel operating circuit having a signal line common to the first, the signal line coupled to both the first and the second photosensing structures.
Additional features and benefits of the invention will become apparent from the detailed description, figures, and claims set forth below.
REFERENCES:
patent: 5471515 (1995-11-01), Fossum et al.
patent: 5721422 (1998-02-01), Bird
patent: 5812192 (1998-09-01), Ishigami et al.
Blakely , Sokoloff, Taylor & Zafman LLP
Intel Corporation
Le Que T.
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