RU2222874C1 - Optical radiation video converter - Google Patents

Abstract

FIELD: multicomponent photosensitive devices. SUBSTANCE: video converter has matrix of photocells 1, each line of matrix being connected to read buses 2 through MOS transistors 3 whose gates are connected through bus 4 to line selection register 5; buses 2 are connected to read station through coupling transistor 7 whose gates are connected to coupling control buses 8; read station has read transistor 9 whose gate is connected to control bus 10 through its charging capacitor; it also has read diode 11 connected to gate of selection and storage transistor 13, source of recharge transistor 12 being connected to power bus 14 and gate, to recharge control bus 15; source of transistor 13 is connected to drain of item-by-item line selection transistor 15; drain of transistor 13 is connected to output signal bus connected to load resistor; read diode 11 is formed by source of transistor 9 and drain of transistor 12. EFFECT: simplified design, reduced supply voltage. 2 cl, 2 dwg

Description

 The present invention relates to multi-element photosensitive devices.

 Known video converters of optical radiation, made in the form of multi-element matrix radiation detectors, in which the charge from the photosensitive area to the output amplifier moves through the charge transfer registers (K. Seken, M. Thompset "Devices with charge transfer", M., Mir, 1978 ) The main disadvantages of such devices are sequential sampling of video information when reading a frame, the need to allocate a significant area of the photosensitive field for charge transfer registers.

 A known optical radiation video converter is a multi-element radiation detector in which the charge accumulated in the photosensitive element (PSE) determines the current of the control transistor of the source follower located in the matrix cell, the load of which is connected to the signal bus. Control of video signal readout is carried out using CMOS multiplexers, allowing the organization of sequential or arbitrary sampling of frame elements (see US Pat. No. 5,933,190, NKI 348-302, 1999). The disadvantage of such devices is the need to place three transistors in each matrix cell, which reduces the matrix cell area useful for photosensitivity.

 Known for the prototype video converter of optical radiation, containing a matrix of photosensitive elements, line-by-line connected to vertical read buses through MOS transistors, the gates of which are connected via horizontal buses to the shift registers of row sampling, the read buses are connected through communication transistors to a read unit consisting of a read diode , a sampling and storage transistor, a bitmap transistor connected to shift registers of a bitmap row sampling, and the cascade of the charge converter, consisting of three transistors (see. Japan 2714293, IPC 6 H 04 N 5/335, 1997). Reading information from the matrix radiation receiver is carried out according to the line-frame sampling scheme. According to this scheme, a row is selected using one shift register, and a column is selected using the second shift register. The photosensitive diode is recharged when the charge is read from it, and the read diode is recharged line by line after reading the information from the selected line.

The disadvantages of the prototype are:
1. The structural complexity of the charge-to-voltage converter using 9 transistors from a photosensitive diode to a signal bus.

 2. The need to use an additional potential difference to obtain a sufficiently high output voltage, as well as subtracting the background charge.

 3. The design does not allow changing the charge accumulation time.

 The technical result when using the present invention is to simplify the design of the charge-to-voltage converter, to provide the possibility of applying a lower supply voltage to the circuit, and to add functionality to the circuit by introducing control of the charge storage time.

 This is achieved by the fact that in an optical radiation video converter containing a matrix of photosensitive elements connected row-wise to vertical readout buses through MOS transistors, whose gates are connected via horizontal buses to a shift register of row samples, vertical readout buses are connected through communication transistors, whose gates are connected to communication control bus, with a reading unit, consisting of a reading transistor, the gate of which is connected to the control bus of their charge capacity of the readout diode formed by the source of the readout transistor and the drain of the recharge transistor and connected to the gate of the sample and store transistor, while the source of the reload transistor is connected to the power bus and the gate to the charge control bus, the source of the sample and store transistor is connected to the drain of the element transistor the source of which is connected to the power bus, and the gate is with the shift register of the element-wise row sampling, and the drain of the sampling and storage transistor is connected to the output signal bus, Connecting to a load resistor. Gates of MOS transistors connecting photosensitive elements with vertical buses, horizontal buses are also connected to a shift register for controlling the exposure time.

 New in the proposed device is that in it the read transistors are connected directly to the readout diodes. In addition, the exposure time control register is additionally connected to the control bus of the transistor for connecting photosensitive elements with vertical buses.

 The simplification of the design is ensured by the fact that the proposed circuit excludes the cascade of charge conversion consisting of three transistors.

 Since there is a direct connection between the supply voltage and the applicable design standards (sizes of circuit elements and the distance between them), the importance of lowering the voltage and unifying the power of all circuit elements is obvious. The use of reduced design standards allows you to increase the ratio of the area of the photosensitive element to the total area of the matrix cell, which improves the output characteristics of the radiation receivers, including the threshold sensitivity. Lowering the supply voltage reduces power consumption.

The invention associated with a change in design and control modes of its elements is illustrated by drawings. In FIG. 1 and 2 are an electrical diagram and a clock diagram, respectively, where
1 - photosensitive elements (diodes, Schottky diodes, etc.),
2 - vertical tires,
3 - MOS transistors for connecting photosensitive elements with vertical buses,
4 - horizontal tires,
5 - shift register of row selection,
6 - shift register control exposure time,
7 - communication transistors,
8 - control bus transistors for communication of vertical buses with a reading unit,
9 - reading transistors,
10 - bus control charge capacitance of read transistors,
11 is a reading diode,
12 - recharge transistors,
13 - transistors sampling and storage,
14 - power bus
15 - bus control transistor recharge,
16 - transistors of element-wise sampling,
17 is a shift register of element-wise selection of a row,
18 - bus output signal
19 - load resistance.

The video converter of optical radiation contains a matrix of photosensitive elements (PSE) 1, composed of N lines and each line contains K elements. PSE 1 line-wise connected to the vertical read buses 2 through MOS transistors 3, the gates of which are connected via the horizontal buses 4 _{(1 ... N)} to the shift registers for selecting rows 5 and controlling the exposure time 6. Vertical read buses are connected through communication transistors 7 _{( 1 ... K)} , the gates of which are connected to the communication control bus 8, with readout nodes consisting of sensing transistors 9 _{(1 ... K)} , whose gates are connected to the control bus of their charge capacity 10, reading diodes 11 _{(1. ..K)} formed by the sources of reading transistors 9 and drains of the transistor 12 _{(1 ... K)} and connected to the gates of the sampling and storage transistors 13 _{(1 ... K)} . The sources of the recharge transistors 12 are connected to the supply bus 14, and the gates are connected to the recharge control bus 15, the sources of the sampling and storage transistors 13 are connected to the drains of the element transistors 16 _{(1 ... K)} , the sources of which are connected to the power bus 14, and the gates - with a shift register of element-wise sampling of line 17, and the drains of the sampling and storage transistors 13 are connected to the output signal bus 18 connected to the load resistance 19.

 The work of the proposed scheme for converting the charge accumulated in the photosensitive element to voltage is carried out as a variant of a matrix radiation receiver with line-frame reading organization. At the same time, shift registers are used as control schemes for selecting rows for reading, recharging, and element-by-element selection of row elements.

 The photosensitive elements of the matrix, for example photodiodes, are connected line-by-line with the shift register of the row selection 5 to the vertical buses when a trigger voltage is applied to the horizontal bus 4 connected to the gates of the MOS transistors 3. In this case, the unlocking voltage is also supplied to the communication transistors 7 and the reading transistors 9, and the charge accumulated in the PSE passes to the gates of the reading transistors 9. After that, the MOS transistors 3 and the communication transistors 7 are closed.

 The charging capacity of the reading transistors 9 (in the prototype, the potential of the gate of a similar transistor is kept constant) is determined by the area of the gate and the level of voltage applied to it when reading the charge. The maximum level of applied voltage is determined by the design standards, and the area should be sufficient so that the electric capacitance at maximum voltage is not less than the capacity of the PSE. This allows you to fully select the accumulated charge. If there is a background component in the accumulated charge package, the sample voltage on the read capacitance control bus 10 is set sufficient to read the information part, and the background component will be removed through the transistors 12 from the read circuit during recharging.

When the voltage on the bus 10 decreases with the transistors 7 and 12 of the buses 8 and 15 closed, the charge from under the gates 9 ₁ -9 _K goes to a readout unit having a relatively small electric capacitance, which will lead to a change in the gate potential of the sample transistors amplified in the ratio of these capacities and storage 13. Signals proportional to the gate potentials of the sampling and storage transistors 13 are alternately read when the register of element-wise sampling 17 unlocks potentials to the transistors 16 and is read through the bus 18 with a load resistance 19. It is not necessary to increase the supply voltage.

 The recharge cycle is necessary to restore potential on the PSE in the entire reading circuit. To do this, after reading the signals from the selected line by bit by bit, the unlocking potentials are fed to the horizontal buses 4, buses 8, 10 and 15, and the horizontal bus potential is determined by the additional reload time control register 6.

 In the design of the prototype, the recharging of the photosensitive element is combined with reading, while the accumulation time of the charge will be equal to the reading time of the frame. The introduction of an additional register allows recharging of photodiodes of any row, regardless of the time of reading information from it, that is, to implement the function of reducing the charge accumulation time. When the accumulation time is equal to the accumulation time of reading the frame, reloading of the selected line is carried out immediately after the completion of the reading process. Reducing the charge accumulation time allows you to work in a wider range of illumination.

To work in the mode with adjustment of the accumulation time after the completion of reading information from the selected, for example 4 ₁ , line in the recharge cycle, line 4 _n is selected. In this case, the accumulation time on the photosensitive elements after recharging t will be equal to:
t = T (Nn) / N,
where T is the reading time of the frame;
N is the number of rows in the matrix;
n is the number of lines skipped when recharging after reading.

 The proposed design was developed for an IR optical video converter with PSE with a Schottky barrier based on platinum silicide. An analysis of the application of design standards of 1.2 μm with a pixel pitch of 36 • 27 μm shows the possibility of obtaining a fill factor of up to 56% and operability with a supply voltage of 5 V. When implementing a similar design with the video converter circuit described in the prototype, it is necessary to increase the supply voltage, which will lead to to changes in design standards and the deterioration of output parameters by 1.5-2 times.

Claims (2)

1. An optical radiation video converter comprising a matrix of photosensitive elements connected row-wise to vertical readout buses through MOS transistors, whose gates are connected via horizontal buses to a shift register of row samples, vertical readout buses are connected through communication transistors, whose gates are connected to a communication control bus, with a readout unit consisting of a readout transistor, the gate of which is connected to the control bus of its charge capacity, readout diode, with the sampling and storage transistor connected to the gate, while the source of the recharge transistor is connected to the power bus, and the gate is connected to the reload control bus, the source of the sampling and storage transistor is connected to the drain of the element-by-line sampling transistor, the source of which is connected to the power bus, and the gate to a shift register of element-wise row sampling, and the drain of the sampling and storage transistor is connected to the output signal bus connected to the load resistance, characterized in that the readout diode is formed by the source readout transistor and drain transistor recharge. 2. The optical radiation video converter according to claim 1, characterized in that it comprises a shift register for controlling the exposure time connected via horizontal buses to the gates of the MOS transistors for coupling photosensitive elements with vertical read buses.

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