RU2671295C1 - Cell of thermocouple ir image receiver - Google Patents

Abstract

FIELD: image processing means; physics.

SUBSTANCE: invention relates to infrared solid-state image receivers, and more particularly to infra-red uncooled solid-state infrared receivers based on thermocouple sensors. Cell of the IR thermocouple receiver contains a thermocouple sensor, a sampling transistor, and a charge-pumping amplifier that consists of 3 charge-coupled field electrodes between adjacent electrodes, an injection-discharge diode, a preset transistor and an input transistor of the source follower performing during the time of the IR image receiver frame the multiple conversion of the information signal into a charge and integration of the latter by the capacitance of the input transistor of the source follower.

EFFECT: invention provides a significant increase in the sensitivity of a thermocouple IR image receiver.

1 cl, 3 dwg

Description

The invention relates to infrared solid-state image pickups, and more particularly, to infrared uncooled solid-state IR image pickups based on thermocouple sensors.

The aim of the invention is to increase the sensitivity of thermocouple IR image receivers.

Cells of thermocouple silicon uncooled IR image detectors are known [1, 2], in which a thermocouple sensor in the form of a dielectric heat-sensitive membrane suspended from a substrate on heat-insulating microconsoles, one end of which is fixed to the membrane, is used as an element that is sensitive to radiation in the infrared region of the spectrum. and the other on the substrate. At least one “hot junction” thermocouple is formed on the surface of the consoles and is located on the membrane, and its “cold” contacts are located on a substrate with a stable temperature. The membrane, heated by the action of IR radiation, raises the temperature of the "hot junction", creating a thermo-EMF between the "cold" contacts. Reading the thermo-EMF arising in the thermocouple due to the temperature difference between the hot junction and the cold contacts is carried out by CMOS circuits integrated directly into the crystal [3].

A distinctive feature of thermocouple sensors is that, having a high signal to noise ratio, they are characterized by a low level of response to thermal radiation. Accordingly, in order to achieve high sensitivity of the IR image receiver based on these sensors, it is necessary to provide a signal amplification in the cell at which the input noise of the amplifier path of the IR image receiver does not reduce the signal-to-noise ratio of the sensor.

The design of the thermocouple sensor cell, which is most often used to implement an IR image receiver, is considered in [4], and is also described in detail in patent application [5], which is selected as a prototype of the present invention. The sensor cells provided in these sources contain a thermocouple sensor and a sampling transistor, which commutes the cells with the preamplifier.

When organizing matrix sensors of IR images on the basis of such sensors, the necessary initial signal amplification is carried out by preamplifiers located on the periphery of the crystal, one for each row (column) of the matrix. In the crystal of an IR image receiver with the number of elements M × N, where M is the number of columns and N is the number of rows, the signal generated by each matrix pixel during the frame time τ _{счит is} read out by multiplexing with sequentially selecting the matrix columns (or rows) of the matrix. This multiplexing method provides simultaneous switching of the elements of the column (or row) with the signal preamps during the time τ _ƒ / M (or τ _ƒ / N). With an increase in the number of elements in the receiver, the time the signal reads by the preamplifiers decreases, which leads to an increase in the frequency band of the amplifier path and, accordingly, to an increase in its noise and a decrease in the sensitivity of the receiver.

In the present invention, this restriction is removed due to the inclusion of a low-noise signal amplification cascade, which is implemented as a charge pump amplifier, which performs multiple conversion of the information signal into a charge and its integration over the course of the IR image receiver frame.

The technical result of the present invention is to increase the sensitivity of the thermocouple IR image receiver due to the amplification of the sensor signal with its multiple summation directly in the cell itself, which also provides an increase in the signal-to-noise ratio.

This result is achieved due to the fact that a charge pump amplifier is introduced into a known cell containing a thermocouple sensor and a sampling transistor, which consists of 3 field electrodes with charge coupling between adjacent electrodes, a charge injection-discharge diode, a preset transistor, and an input transistor source repeater, carrying out during the time frame of the receiver of the IR image, the multiple conversion of the information signal into a charge and the integration of the latter.

The list of graphic materials illustrating the claimed invention.

FIG. 1 illustrates a known cell of a thermocouple IR image receiver (prototype) and a matrix organization scheme of cells of an IR image receiver.

In FIG. 2 shows the proposed cell with a thermocouple sensor and a sampling transistor, which includes a charge pump amplifier consisting of three field electrodes G _B , G _TS , G _c with charge coupling between adjacent electrodes, a charge injection-discharge diode D _i , and a preset transistor T2 and input transistor T3 of the source follower, which during the time frame τ _{кадра of} the IR image receiver, repeatedly converts the information signal V _{TS of the} thermocouple sensor into a charge and integrates the latter on the shutter capacitance C _sum input transistor T3.

In FIG. 3 is a pulse diagram providing the operation of the cell of FIG. 2.

The cell in FIG. 2 operates as follows (FIG. 3).

1. The thermocouple sensor TS connected between the electrodes G _B and G _TS creates between them a small potential difference V _TS generated by the TS sensor under the influence of IR radiation. The electrodes G _B and G _TS are biased by a voltage V _B , which forms conductivity inversion regions under these electrodes in the surface regions of the semiconductor substrate. At the beginning of the frame at time τ _{1, the} injection-discharge diode D _i is biased in the opposite direction, the output electrode G _{c is} locked (Ф _set = 0), and the voltage pulse Ф _set on the gate of the preset transistor T2 charges the capacitance C _sum equal to the sum of the capacitances the gate of the transistor T3 and the source S _{T2 of the} transistor T2, to the potential V _DD . The cell returns to its original state.

2. At the time t = τ _{2, the} injection-discharge diode D _i is displaced in the forward direction (Ф ₁ = 0), injecting a charge under the electrodes G _B and G _TS over time and then passing at the time t = τ ₂ + τ _i to the reverse biased state. Thus under electrode G _TS remains part of the injected charge ΔQ _n = C _TS V _TS, where C _TS - capacitance electrode G _TS.

3. At time t = τ ₃ , the electrode G _c opens and the charge ΔQ _n is read onto the capacitance C _sum , decreasing the gate potential of the transistor T3 by

4. The cycles of converting the information signal V _TS into a charge and its reading described in paragraphs 2 and 3 are repeated n times. Due to this, during the frame time τ _ƒ , n-fold summation of the charge on the capacitance C _sum and

после чего на транзистор выборки подается импульс напряжения Ф_reset, производящий считывание интегрированного информационного сигнала на вход внешнего предусилителя. Таким образом, коэффициент усиления ячейки, приведенный ко входу истокового повторителя, составляет величину, равную:the gate potential of the transistor T3 by

after which a voltage pulse Φ _reset is applied to the sampling transistor, which reads the integrated information signal to the input of an external preamplifier. Thus, the cell gain, reduced to the input of the source follower, is equal to:

For a thermocouple sensor, V _TS = αΔT _TS , where α is the Seebeck coefficient, reaching 300 μV / K for a sensor with polycrystalline silicon thermocouples, and ΔT _TS is the temperature difference between the hot junction and the cold contacts of the thermocouple. The temperature difference ΔT formed on the sensor membrane is determined by its thermophysical parameters and the amount of absorbed thermal radiation:

- постоянная времени, характеризующая время реакции мембраны сенсора на изменение мощности теплового излучения, С - теплоемкость мембраны [Дж/K]. Стационарное значение ΔT_TS определяется следующим выражением:where G is the thermal conductivity of the thermocouple, ΔP is the power of the thermal radiation absorbed by the sensor,

- the time constant characterizing the reaction time of the sensor membrane to a change in the power of thermal radiation, C is the heat capacity of the membrane [J / K]. The stationary value ΔT _TS is determined by the following expression:

where h _t is the thickness of the thermocouple, g _t is the specific thermal conductivity of the material (polysilicon) of the thermocouple, Δp is the excess radiation power of the absolutely black bodies absorbed by the unit area of the membrane, w is the width of the thermocouple, L is the length of one arm of the thermocouple, and A is the area of the heat-receiving membrane of the sensor. It is taken into account that the thermal conductivity of the thermocouple is the sum of the thermal conductivities of each of the two arms of the thermocouple and, accordingly, is equal to

Taking into account that (Δp / ΔT) = ηqj, where ΔT is the change in the temperature of the thermal scene, η is the fraction of the incident radiation absorbed by the heat-receiving membrane, q is the optical factor equal to q = Ht _o / 4, where H is the aperture, t _o - the transmission of the lens, and j≈2.62 W / m ² ⋅K for the range of 8 ÷ 14 μm, we obtain:

Then, for a sensor with a polysilicon thermocouple and parameters that can be implemented by MEMS technology with design standards of 0.35 μm, namely, h _t = 0.2 μm, w _t = 2 μm, А≅2500 μm ² , L≅60 μm , and also taking into account g _t = 25 W / m⋅K, η = 0.8, H = 1, t _o = 0.9, we obtain:

and correspondingly,

Based on this, with a thermal relief of the scene of the order of 80 K, it is necessary to reproduce signals from the sensor to V _TS ≈100 μV.

получим для максимального число циклов n_max:Assuming, taking into account the magnitude of the supply voltage V _DD = 3.0 V, the maximum range of changes in the potential of the summing capacitance C _{sum is} equal to ΔV _sum = 1.0 V, and also taking into account the technologically possible ratio

get for the maximum number of cycles n _max :

Accordingly, the maximum gain realized by the proposed cell in this case will be equal to:

что существенным образом снижает требования к усилителям на периферии кристалла.In this case, the signal-to-noise ratio in comparison with the prototype can be increased to a maximum value equal to

which significantly reduces the requirements for amplifiers on the periphery of the crystal.

Information sources

1. US Patent No. US 8,592,765 B2

2. US Patent No. US 6,163,061

3. US Patent No. US 7842922

4. M. Hirota, Y. Nakajima, M. Saito, F. Satou, M. Uchiyama, 120 × 90 Element Thermopile Array Fabricated with CMOS Technology, Proceedings of SPIE Vol. 4820 (2003), pp. 239-249.

5. European Patent Application No. EP 2312286 A1

Claims (1)

A cell of a thermocouple infrared image detector containing a thermocouple sensor and a line sampling transistor, characterized in that in order to increase the sensitivity, a charge pump amplifier is introduced into the cell, which consists of 3 field electrodes with charge coupling between adjacent electrodes, an injection-discharge diode , a transistor of preset and an input transistor of a source follower, carrying out multiple conversion of an information signal into a charge and s last capacitance of the source follower input transistor.

Images