JPS5846068B2 - charge-coupled device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charge-coupled device (C) used for line or area imaging.
Regarding CD).

Charge-coupled semiconductor devices were first developed by W, S, Boyle and G,
It was invented by E. Sm1th.

This is described in U.S. Pat. No. 3,858,232, entitled "Charge Coupled Semiconductor Device" by Boyle and Sm1th, Bell System Technical Journal, Volume 49, Page 587.

Since then, the development of charge-coupled devices has been described in many publications.

For example, in Scientific American, February 1974, Volume 230, No. 2, Page 23, G11bert
A "charge-coupled device" is often shown in F. Amelio.

It is now well known that line and area imaging devices are fabricated with arrays of charge storage devices and that such devices are commercially available.

For example, the products CCD101 and CCD110 of the applicant Fairchild Camera and Instrument Corporation (hereinafter referred to as Fairchild)
, CCD121, and CCD201.

In suitable known constructions, the charge stored in the illumination aperture is transferred to and from the shift register by applying an appropriate signal and sensed;
Amplified or utilized by an electrical circuit.

Unfortunately, prior art charge-coupled imagers were unable to provide an internally generated reference signal indicative of the intensity or color tone of the light applied to the illumination aperture of the CCD.

In other words, it was only possible to provide information about the relative intensity of light falling on a particular illumination aperture in comparison with other illumination apertures.

The video output signal of a charge-coupled imager is applied to a DC level of several volts, for example +7 to +10 volts, so that only relative information is generated.

This DC level is typically set by a reset circuit, a floating gate potential, or an amplifier bias point and supply potential.

The precise voltage levels of the black and white signals of conventional CCDs have been set only by operating the COD in the dark and with appropriate optical conditions to produce saturation or near saturation.

Even when performed in this manner, the calibration of settings made in such tests is subject to drift due to changes in equipment operating conditions, such as ambient temperature, supply voltage, or circuit drift.

Furthermore, prior art charge-coupled devices are designed to reset and/or recirculate the charge-coupled device to transfer a new set of signals to the shift register after the entire previous series of data has been transferred from the shift register. Requires a relatively large amount of external circuitry.

For example, in a conventional line imager, a series of counters
Used to ascertain the number of cycles of the transfer signal supplied to the elements of the shift register before moving the transfer gate to transfer the new set of signals represented by the packets of charge from the illumination aperture to the shift register. .

This peripheral circuitry makes systems using CCDs multiple and increases cost.

The CCD structure of the present invention is used to provide black and white reference signals representing the minimum and maximum light, respectively, that the CCD can sense.

The black reference signal is generated by one or more optically dark and electrically isolated light sensitive regions of the CCD.

If light is prevented from hitting these illumination apertures, the signal from the illumination apertures will indicate the absence of light.

That is, it represents the black reference signal.

This black signal is transferred from one or more illumination apertures to a shift register and then transferred out of the CCD, where it is used as a reference signal for comparison with other signals from the CCD and sensed by the COD. Provide the darkest possible optical conditions.

A white signal is generated at a selected level representing a somewhat brighter, or less dark, condition that the CCD senses.

This is done by injecting a predetermined maximum amount of charge into one or more elements of the CCD shift register.

When these signals are transferred from the CCD, they are
provides a reference signal indicative of a selected bright optical condition sensed by the optical sensor.

Moreover, by injecting a predetermined amount of charge, either less or more, a reference signal is created that indicates the desired neutral color of gray or white.

The generation of black and white reference signals provides a fixed point at each end of the gray stage, thereby determining the optical range that the CCD senses.

Providing a reference signal that also recognizes the linearity of the CCD response over the entire optical range allows the CCD user to accurately measure the gray intensity of the optical conditions sensed by the CCD.

In one embodiment, the amount of charge injected to generate a white signal represents the brightest signal that can be linearly reproduced, rather than the brightest optical state that the COD senses (corresponding to saturation of the illumination aperture). .

Using this white and black signal, all intermediate signals generated by the CCD are measured linearly between black and white to accurately sense the colors between each of these, thereby ensuring their accurate retention and transfer. , or facilitate playback.

This is utilized, for example, by facsimile machines.

The charge packets, e.g. the white signal, are placed in an additional separate shift register which does not have an illumination aperture but has many elements similar to other CCD shift registers used to receive and transmit signals from the illumination aperture. An end-of-scan indication signal is generated by injecting a similar signal.

That is, the signal is injected into the farthest end of the shift register and is the only signal for that shift register.

By stepping this signal out of an empty shift register at the same rate that the signal generated by the illumination aperture is stepped out of its corresponding shift register, the signal is caused to start a new scan of the shift register. Used to provide a direct positive electrical command to reset the CCD.

In one embodiment, the white signal is generated by a diode that receives signals from a pair of MOS transistors.

The source of the single MOS transistor is connected to the drain of the second MOS transistor, and a bias voltage is applied to the drain and gate of the second MOS transistor.
The source and gate of the OS transistor are connected to each other.

By appropriate design of the first and second transistors, a fairly constant voltage can be supplied to the input diode.

The charge on the human diode is then transferred to the elements of the shift register in response to the same clock signal that transfers the collected charge from the illumination aperture to the shift register.

By suitably designing the MOS transistor and supplying it with suitable voltages, the injected charge can be made to the desired amount.

FIG. 1 shows a schematic plan view of an embodiment of the invention applied to a 1728 element linear imaging array.

Fairchild product CCD121 is cited as an example of a product prior to the present invention.

FIG. 1 shows 1728 illumination apertures that generate electrical charges in response to electromagnetic radiation impinging on them.

In a known manner, the charges collected in each illumination aperture are sent simultaneously to one of the two shift registers 10 or 11.

As shown in the first diagram, for example, the charges collected in the odd-numbered irradiation apertures are transferred to the shift register 11, while the charges collected in the even-numbered irradiation apertures are transferred to the shift register 10.

Shift registers 10 and 11 are each divided into two separate shift registers by a separation region 12.

Charge transfer from the irradiation apertures 1 to 1728 to the shift register 10.11 is performed by applying a signal φ to the electrode 14.

This technique is well known in CCD technology, but
It is explained in more detail in the figures.

Mutual interference of signals in adjacent elements of the CCD shift register causes the charges in the odd-numbered illumination apertures to flow in one direction, i.e., in the register 11.
and by transferring the charge of the even illumination aperture in the other direction, ie to the register 10.

Charge packets are thus transferred to each of the shift registers 10.11.

For example, the charge collected on the illumination aperture 1 is transferred to the area under the electrode 21, while the charge collected on the illumination aperture 3 is transferred to the area under the electrode 23.

This is because no charge is transferred under electrode 22.
1.23 is maintained at a different potential.

Therefore, the signals transferred to the area below the electrodes 21, 23 are spared from coming together and the resulting loss of information.

As shown in the first diagram, the signal from the illumination aperture 2 is transferred below the electrode 32.

The charges of 1728 irradiation apertures are transferred to shift register 10.1.
1, the potential of the signal φX is changed and a new string signal begins to collect within the 1728 illumination apertures.

Thereafter, by applying appropriate signals such as φT and VT to the shift register elements, the signals under the electrodes are stepped out of the shift register 10 and the shift register 11 is stepped out.
The lower part of is transferred to the output gate.

The transfer of these signals to the output gate is indicated by the arrow 30 in FIG.
31.

Output gate structures are well known in the art.

For example, it is shown in US Pat. No. 3,999,082 entitled "Charge Coupled Amplifier".

In one embodiment of the invention shown in FIG.
The signals from the illumination apertures are not transferred to the lower part of shift register 10 or the upper part of shift register 11.

Transfer of charge to these portions of the shift register is impeded by isolation regions 12, typically oxide, which effectively divide each shift register 10.11 into two separate shift registers.

Transfer of charge from each shift register electrode to the next may be effected by channel regions 15 between barriers 58 extending below the electrodes.

The upper portion of shift register 11 and the lower portion of shift register 10 prevent stray charges in the substrate from flowing to the elements of the shift register and distorting the information stored therein.

That is, stray charges are collected and harmlessly disposed of by these separate shift registers.

Arrows 33 and 40 indicate the transfer of these stray charges to the sink region or power supply.

However, as discussed below, in some embodiments the signal indicated by arrow 40 is provided to external circuitry.

The black and white reference signals are generated by the CCD structure shown in FIG. 1 as described below.

In the exemplary embodiment, the black reference signal is transmitted through several optically and electrically separated additional illumination apertures Bl, B2 . Generated by B3.

Any number of such irradiation apertures can be provided without droplets.

The irradiation aperture B1 (and B2 and B3) is divided into active irradiation apertures 1, 2...1 by the isolation area ■.
728.

These irradiation apertures are 1°2...172
It will be appreciated that they may be located anywhere within or along 8 as desired.

In particular, such an illumination aperture is a normal active illumination aperture 1...
... 1728, located at one end or the other end of the illumination aperture, or both ends, or a combination thereof.

In FIG. 1 they are shown at the right end of the linear array.

Black irradiation aperture B'l, B2. B3 is typically separated from the active illumination aperture by an isolation cell.

This means that the charge in any of the active cells is the black reference cell Bl,
This prevents leakage to either B2 or B3.

In addition, in this manner, the manufacturing tolerances for forming the window 35 can be relaxed.

Window 35 allows electromagnetic radiation, typically visible light, to impinge on the illumination aperture.

Although not shown in FIG. 1, there is a black reference cell Bl around the window 35.

B2. There is a light shield that prevents light from hitting B3.

In some embodiments of the invention, window 35 is a material that is opaque to visible electromagnetic radiation of a predetermined wavelength, even if, for example, a blue or other color signal is to be sensed.

The position of the window 35 is the black reference irradiation aperture B1. Since they prevent light from hitting B2 or B3, these illumination apertures do not collect any charge, ie they collect a charge that represents the entire state of the substrate excluding the effects of visible light.

In this way, the black reference irradiation aperture B1. B2. B3 automatically corrects for dark current or other errors due to temperature or chemical composition, or other ambient conditions.

One technique for producing a white reference signal is shown at the left end of shift register 10.

By applying the signal vR to the diode 38,
The signal charge is supplied to the diode, and when the potential of φX increases appropriately, the shift register elements 39, 42? This will be transferred.

As discussed with respect to Figures 4a-4e, this charge is suitably sized to represent a saturated brightness level or other desired reference charge level such as a less bright condition or gray.

This charge is referred to herein as the white reference signal.

That portion of the charge injected into shift register element 42 by adding signals vT and φ1 is transferred to shift register 1 following the transfer of the signal charge produced by the 1728 illumination apertures.
Transferred from 0.

The white reference signal may be injected at other desired locations along shift register 10 by suitably modifying the structure shown in FIG.

That portion of the white reference signal injected below electrode 39 is used as an end-of-5can indication.

That is, by placing the white reference signal at the farthest end of shift register 10, as shown in the first illustration, the signal transferred below electrode 39 emerges from shift register 10 after the signal produced at illumination aperture 1728.

Therefore, the white reference signal is also used as an electrical signal indicating completion of signal transfer from the shift register 10.

In contrast, prior designs required a separate counting device to find the appropriate time to provide signal φX.

The white reference signal from area 38, when transferred from the lower portion of shift register 10, is transferred to some well-known external logic circuit, which then operates signal φX.

Figure 2a is a partial cross-sectional view of the structure shown in Figure 1 when constructed using buried channels.

Isolation regions 51a and 51b, typically made of silicon diodes, are formed in series on a substrate 50, which is typically of P conductivity type.

P+ conductivity type region 53a. 53b may be formed under the isolation region 51 to prevent floating ions from forming a conductive path under the isolation region 51.

The N conductivity type regions formed in substrate 50 collect charge in response to surrounding electromagnetic radiation.

Buried channel regions 56at56b, typically doped with phosphorous, arsenic, or other N-type materials, and regions 58a, 58b, typically doped with boron or other P-type materials.
t 58c forms a barrier region that changes the potential phase diagram of the structure, as discussed below.

Also shown in FIG. 20 are electrodes on the substrate 50.

Electrode 59a is connected to receive signal φT, while electrode 61a is connected to receive signal φX.

Electrode 62 is connected to receive signal VPG.

Immediately below the structure shown in FIG. 2a are sections 2b, 2c, and 2c showing how the charge 73 collected in region 55 is transferred to the region below electrode 59a when signal φ is applied. 2
A series of potential state diagrams in diagram a are shown.

Once the charge has been transferred, it is transferred from the CCD by applying the signals φT and vT as described in FIG.

The potential state diagram shown in FIG. 2b shows the state of the structure shown in FIG. 2a when the signals .phi. and .phi.T are each at zero potential.

In this state, charge collects in the potential well created by region 55.

The collected charge is indicated by the shaded area 73 in Figure 2b.

Next, as shown in FIG. 2c, by increasing the potential of the signal φX, the potential well under the electrode 61a is deepened, and part of the charge 76 is transferred from the region 55 and temporarily stored under the electrode 61a. It will be done.

Next, as shown in FIG. 2d, the potential of signal φT increases, whereby the charge 76 stored under electrode 61a is transferred under electrode 59a and stored in region 56a.

Once the charge 78 is stored in the region 56a under the electrode 59a, the potential of the signal φX is lowered and the appropriate signal φT,
VT converts the charge 78 in the region 56a under the electrode 59a to CCD.
Further charge is prevented from being transferred from region 55 to region 56a until it is applied to transfer from the device to other electrical circuitry as desired.

FIG. 3 shows a series of CCD light sensing elements, 1725.1, at the end of the active cell opposite the black cell shown in FIG.
A cross-sectional view of a series of four black reference cells as placed to the left of 726, 1727, 1728 is shown.

Black reference cell B4. B5. B6jB7 are separated from adjacent active cells or other circuitry by isolation cells 11, I2.

The cover 36 prevents visible light from irradiating the black cells B4 to B7.

Cover 36 is a suitable material, such as aluminum.

Cover 36 is typically formed over insulating layer 37 to prevent it from contacting the surface of substrate 50 or areas formed thereon.

Black cells B4-B7 generate signals representing only conditions within the substrate, such as temperature, for example.

Isolation cell ILI2 is a reverse biased N+ diffused diode that serves to remove stray charge carriers within its region.

The isolated cells are simply reverse biased by connecting them to an aluminum light shield 36 as shown in FIG. 3 and then applying the desired potential to the shield 36.

FIG. 4a is a partial sectional view of FIG. 1, showing the operation of the white reference signal generator as well as the operation of instructing the end of scanning.

The reference numerals for the structure shown in FIG. 4a are the same as those for the structure in FIG.

To generate the white reference signal, two MOS transistors 71, 72 are used to generate a signal vR applied to region 38.

As shown in FIG. 4a, the gate electrode of transistor 71 is connected to receive signal vT, while the drain electrode is connected to receive signal VDD.

MOS transistor 72 has a gate electrode connected to a source electrode connected to ground.

In practice, transistor 72 provides a constant current source to transistor 71 since it produces a signal vR substantially equal to vT minus the threshold voltage.

By appropriate selection of transistors 71, 72, signal VR is selected to inject the desired amount of charge.

The maximum amount of charge injection packets that the shift register receives from the illumination aperture, ie, the amount of saturated charge, is determined by the barrier height vB created by barrier 58 and the physical dimensions of the area or region 80 into which it is transferred. Ru.

Area 77 in FIG. 4d graphically represents this quantity.

However, the amount of charge actually transferred from region 38 may be less as determined by the potential barrier VB created by barrier 58, which is the physical dimension of region 68.

This amount of charge is shown diagrammatically as area 75 in FIG. 4e.

Since the height of the barrier is equal in both cases, the physical dimension 68 is adjusted to limit the white signal charge to a selected small fraction of the saturated charge corresponding to the upper limit of the linear range of sensitivity of the CCD illumination aperture, for example. be done.

One advantage of generating a white signal as described above is that the magnitude of the signal can be changed by changing the structure dimensions without changing the processing parameters.

Since the dimensions are controlled more precisely than the processing parameters, the white signal can be controlled more precisely.

This linearity allows a signal to be generated by any illumination aperture area 1-1728 that is precisely related to the gray linear region between black and white.

The charge collected in region 38 as a result of signal vR from transistors 71, 72 is transferred along the upper portion of shift register 10 shown in FIG. 1 to produce a white signal as shown in FIGS. 4b-4e. is supplied to other circuits to supply

As shown in FIG. 4b, when signal φX is low, it is due to the total charge 7 collected in region 38 as a result of signal vR.
Create a potential barrier that stores 4.

Next, as shown in FIG. 4e, the area 38 is
The charge 74 within also collects below the electrode 14.

However, the signal φT held at a low potential is
This prevents charge 74 from being transferred from the electrode 39 to the electrode 39.

Thereafter, as shown in Figure 4d, the potential of the signal φT supplied to the electrode 39 increases, while the signal vT supplied to the electrode 65 is maintained at the previous level.

This causes charge 74 from below electrode 14 to be transferred to below electrode 39.

Next, as shown in Figure 4e, the potential of the signal φT supplied to the electrode 39 decreases.

In fact, this lowers the potential φT which separates the charge of portion 75 from the bulk of the charge remaining under electrode 14 and in region 38, so that this portion of charge 75 is transferred under electrode vT.

Thereafter, the charge packet 75 is gradually transferred from one electrode to the next by a series of pulses of the signal φT, and finally reaches the right-hand end of the upper portion of the shift register 10 shown in FIG. As shown, the signal is supplied to other circuits as necessary.

In a manner similar to that described above in connection with the upper part of shift register 10, the signal injected below electrode 39 is transferred to electrode 4.
Injected under 2.

This signal is generated by 1728 illumination apertures.
Following the 728 signals, a scan end signal is supplied.

Thereby, the injected charge is used in a well-known manner to activate other electrical circuits and expose the CCD to illumination apertures 1-172.
8 to transfer a new set of charges to the shift register.

The structure of the present invention has many advantages over conventional structures.

In particular, the black reference cell is a black reference that compensates for dark current signals, for temperature effects, for changes in the clock signal, for changes in the output amplifier, and generally for errors induced in the entire photosensitive area. supply the signal.

On the other hand, a white reference cell provides many advantages by generating a signal representing the desired brightness of white light or gray.

Moreover, the same white reference signal, when injected into a remote shift register, acts as an end-of-scan indication to reset the operation of the CCD device, thus eliminating the need for counting circuits used in conventional high-capacity CCD devices. It becomes necessary.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the structure of one embodiment of the present invention, Figure 2 is a schematic diagram showing the structure of an embodiment of the present invention.
Figure a is a partial sectional view of the structure in Figure 1, and Figure 2b-2d is a partial cross-sectional view of the structure in Figure 1;
Figure 2a is a potential energy state diagram for the structure of Figure 2a showing how charge packets are transferred from the illumination aperture to the shift register; Figure 3 is a cross-sectional view of a set of black reference cells; Figure 4a is a cross-sectional view of a set of black reference cells;
Figure 4 is a schematic diagram showing one method of generating a white reference signal.
Figure b-4e shows how a charge packet (white reference signal) is transferred from one element of the shift register to the next in a shift register that transfers an end-of-scan indication signal or a conventional CCD shift register. FIG. 2 is a potential energy phase diagram of the structure of 10.11...Shift register, 12...
... Separation region, 14 ... Electrode, 1 to 1728.
...Irradiation aperture, B1. B2. B3...Black irradiation aperture, 35...Window, 3B...Diode, 50...Substrate, 51a. 51b... Separation area, 71, 72...
transistor.

Claims (1)

[Scope of Claims] 1. A plurality of collection means each collecting charge packets in response to light, and at least one first transfer means for transferring the collected charge from each collection means to a second transfer means. , a second transfer means for transferring the plurality of collected charges to the signal processing means, at least one dark collection means for collecting charge packets indicative of the absence of light, and a selected intensity of the light. at least one bright collection means for collecting charge indicative of the output signal, third transfer means for supplying the charge collected by the dark and bright collection means to the signal processing means, and a plurality of charge packets represented by charge-coupled device for generating a signal indicative of ambient light conditions, characterized in that the device comprises signal processing means for obtaining information about ambient light conditions. 2. A charge-coupled device according to claim 1, wherein the second transfer means and the third transfer means are the same means. 3. The device according to claim 1, comprising logic means for generating a first signal for moving the first transfer means, and logic means for transmitting a portion of the charge collected by the bright collection means to the logic means. a fourth transfer means connected thereto, thereby causing the logic means to generate the first signal. 4. The apparatus of claim 1, wherein each dark collection means is an illumination aperture of a charge-coupled device, and light is prevented from entering each illumination aperture by an optically opaque cover, and the light collection means is an illumination aperture of a charge-coupled device. is a diode connected to an electrical signal source, and the second transfer means is a first shift register. 5. A device according to claim 4, characterized in that each collection means is an illumination aperture of a charge-coupled device, and the second transfer means are both a second shift register and a first shift register. Charge-coupled device. 6% The charge-coupled device according to claim 3, wherein the fourth transfer means is a third shift register. 7. The device according to claim 1, wherein the light collection means is a diode freely connected to the third transfer means, and the first and second transistors are connected to the diode for supplying signals thereto. A charge-coupled device characterized by: 8. In the device according to claim 7, the first and second transistors are insulated gate field effect transistors, the source of the first transistor is connected to the drain of the second transistor, and the source of the second transistor is connected to the drain of the second transistor. The gate is connected to ground potential, and the selected electrical signal is supplied to the source and gate of the first transistor.
A charge-coupled device characterized in that the source of the transistor is connected to a diode. 9 a plurality of light-sensing illumination apertures, a first signal output means, first and second shift registers for transmitting signals from the illumination apertures to the signal output means, and an opaque cover whose light is blocked by means. a selected number of illumination apertures, an input diode connected to a second shift register, a circuit for supplying a signal to the input diode, a second signal output means, and a second signal output means for transmitting a signal therefrom. A charge-coupled device characterized in that it comprises a third shift register connected to a human power diode for supplying the means. 10. The device of claim 9, wherein the circuit includes first and second transistors connected together to a power source. 11. In the device according to claim 10, the first and second transistors are insulated gate field effect transistors, the source of the first transistor is connected to the drain of the second transistor, and the source of the second transistor is connected to the drain of the second transistor. A charge-coupled device, characterized in that the gate is connected to ground potential, the power supply is connected to the source and gate of the first transistor, and the source of the first transistor is connected to a diode.