CN105352606A - Reading circuit of uncooled infrared focal plane array detector - Google Patents

Abstract

The embodiment of the present invention discloses a readout circuit of an uncooled infrared focal plane array detector, including: a bias thermal stabilization circuit 10, which includes a channel-level reference microbolometer R _b and provides a constant bias setting current; the detection circuit 20 is connected to the detection microbolometer R _s at the pixel level and the bias thermal stabilization circuit 10, and generates a detection output based on the reference microbolometer R _b and the detection microbolometer R _s signal; the integration circuit 30 is connected to the detection circuit 20 and integrates the detection output signal of the detection circuit 20 to obtain an output signal. The readout circuit of the embodiment of the present invention provides a stable current path for the reference microbolometer, realizes the stability of the bias heat, greatly improves the uniformity and reliability of the overall circuit, and greatly improves the high voltage resistance of the circuit and adaptability to the environment.

Description

A Readout Circuit of Uncooled Infrared Focal Plane Array Detector

A Readout Circuit of Uncooled Infrared Focal Plane Array Detector

technical field

The invention relates to the technical field of infrared focal plane array detectors, in particular to a readout circuit of an uncooled infrared focal plane array detector.

Background technique

Night vision technology is divided into two directions: low-light imaging technology and infrared thermal imaging technology. Night vision technology plays an important role in modern warfare. The weapons and equipment equipped with night vision equipment are all over the sea, land and air combat platforms, and are used in large, medium and small weapon systems. Therefore, mastering advanced night vision technology is of vital significance for controlling the battlefield situation. Compared with low-light imaging technology, infrared thermal imaging technology has complex manufacturing process and high production and maintenance costs, but it has significant advantages in terms of working distance, image quality, day and night sharing problems, and applicable fields.

The core technology of infrared thermal imaging technology is detector technology. According to the classification of working temperature, infrared detectors are divided into cooling type and uncooling type. Uncooled infrared thermal imaging technology has the advantages of low price, small size, low power consumption, reliable performance, and convenient operation, and has become an inevitable mainstream technology.

The uncooled infrared focal plane array detector can work at room temperature without refrigeration equipment, and has the advantages of light weight, small size, long life, low cost, low power consumption, fast startup and good stability, etc., which meets the needs of civilian infrared systems. And the urgent need for long-wave infrared detectors in some military infrared systems, so this technology has been developed rapidly and widely used. The readout circuit (ROIC) is one of the key components of the uncooled infrared focal plane array (IRFPA). Its main function is to preprocess the weak signal induced by the infrared detector (such as integration, amplification, filtering, sampling/holding, etc.) ) and parallel/serial conversion of array signals. Depending on the material used and the working method of the detector, the structure of the readout circuit changes accordingly to obtain the maximum signal-to-noise ratio (SNR) while meeting the requirements of the frame rate.

The microbolometer focal plane array (FPA) has high sensitivity and is the most widely used uncooled infrared focal plane array detector. Its working principle is that the temperature of the heat-sensitive material changes after absorbing the incident infrared radiation, which causes the change of its own resistance value, and detects the size of the infrared radiation signal by measuring the change of its resistance value. The microbolometer generally adopts the micro-bridge structure of cantilever beam made by micro-machining technology. The bridge deck is deposited with a layer of heat-sensitive material with high temperature coefficient of resistance (TCR). The bridge leg of the material is supported, and the contact point between the bridge leg and the substrate is a bridge pier, and the bridge pier is electrically connected to a silicon readout circuit (ROIC) under the microbolometer FPA. Through the bridge legs and piers, the thermally sensitive material is connected to the electrical channel of the readout circuit, forming a pixel unit that is sensitive to temperature and connected to the readout circuit. The heat absorbed by the thermosensitive material is mainly from three sources: the temperature change of the thermosensitive material caused by the temperature change of the substrate, the temperature change of the thermosensitive material caused by the absorbed infrared radiation, and the bias heat generated by the bias circuit of the microbolometer The temperature change of the thermosensitive material.

After years of development and technological progress, uncooled infrared focal plane array detectors have met the needs of use in terms of noise, but people have problems with uncooled infrared detector performance, image quality, stability, power consumption, volume and cost. higher requirements.

Contents of the invention

One of the objects of the present invention is to provide an uncooled infrared focal plane array detector that can make the bias heat of the bias circuit of the microbolometer more stable so as to eliminate or reduce the adverse effects caused by the change of the bias heat device readout circuit.

The technical solutions disclosed in the present invention include:

A readout circuit of an uncooled infrared focal plane array detector is provided, which is characterized in that it includes: a bias thermal stabilization circuit 10, and the bias thermal stabilization circuit 10 includes a channel-level reference microbolometer R _b and providing a constant bias current for said reference microbolometer R _b ; a detection circuit 20 connected to a detection microbolometer R _s at the pixel level and said bias thermal stabilization circuit 10 , and generate detection output signals according to the reference microbolometer R _b and the detection microbolometer R _s ; the integration circuit 30, the integration circuit 30 is connected to the detection circuit 20 and detects the The detection output signal of the circuit 20 is integrated to obtain an output signal.

In an embodiment of the present invention, the bias thermal stabilization circuit 10 further includes a chip-level first transistor MP1, a chip-level second transistor MP2, a channel-level third transistor MP3, and a channel-level fourth transistor MP4, Wherein: the source of the first transistor MP1 is connected to the system power supply V _DD , the drain of the first transistor MP1 is grounded through the first constant current source 101 , and the gate of the first transistor MP1 is connected to the first The drain of a transistor MP1; the source of the second transistor MP2 is connected to the system power supply V _DD , the drain of the second transistor MP2 is grounded through the second constant current source 102, and the gate of the second transistor MP2 connected to the drain of said second transistor MP2 and to one terminal of said reference microbolometer _Rb ; the other terminal of said reference microbolometer _Rb is connected to the source of said third transistor MP3 pole; the drain of the third transistor MP3 is connected to the source of the fourth transistor MP4 and connected to the detection circuit 20, and the gate of the third transistor MP3 is connected to the gate of the fourth transistor MP4 pole; the drain of the fourth transistor MP4 is grounded.

In one embodiment of the present invention, the detection circuit 20 includes a fifth transistor MP5, wherein: the source of the fifth transistor MP5 is connected to the drain of the third transistor MP3 and connected to the integration circuit 30, The drain of the fifth transistor MP5 is connected to one end of the detection microbolometer R _s , the gate of the fifth transistor MP5 is connected to the bias voltage V _fid ; the detection microbolometer R The other end of _s is grounded.

In an embodiment of the present invention, the source of the fifth transistor MP5 is connected to the drain of the third transistor MP3 and the integrating circuit 30 through a switch S1.

The readout circuit of the embodiment of the present invention provides a stable current path for the reference microbolometer, realizes the stability of the bias heat, greatly improves the uniformity and reliability of the overall circuit, and greatly improves the high voltage resistance of the circuit and adaptability to the environment.

Description of drawings

Fig. 1 is a schematic structural diagram of a readout circuit of an uncooled infrared focal plane array detector according to an embodiment of the present invention.

Fig. 2 is a simulation diagram of the output voltage of the traditional readout circuit with the target temperature at different substrate temperatures.

FIG. 3 is a simulation diagram of the output voltage of the readout circuit according to the embodiment of the present invention with the target temperature at different substrate temperatures.

detailed description

The specific structure of the readout circuit of the uncooled infrared focal plane array detector according to the embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic structural diagram of a readout circuit of an uncooled infrared focal plane array detector according to an embodiment of the present invention.

As shown in FIG. 1 , in some embodiments of the present invention, a readout circuit of an uncooled infrared focal plane array detector includes a bias thermal stabilization circuit 10 , a detection circuit 20 and an integration circuit 30 .

The bias thermal stabilization circuit 10 includes a channel-level reference microbolometer _Rb and provides a constant bias current to said reference microbolometer _Rb . The detection circuit 20 is connected to the detection microbolometer R _s at the pixel level and the bias thermal stabilization circuit 10 and generates a detection output signal from the reference microbolometer R _b and the detection microbolometer R _s . The integration circuit 30 is connected to the detection circuit 20 and receives the detection output signal of the detection circuit 20, and integrates the detection output signal of the detection circuit 20 to obtain an output signal.

In the embodiment of the present invention, the bias heat stabilization circuit 10 provides a constant bias current for the reference microbolometer R _b , thereby ensuring that the bias heat of the blind pixel in the bias circuit is constant, and greatly improving the overall circuit performance. The uniformity and reliability of the circuit are also greatly improved.

As shown in FIG. 1, in some embodiments of the present invention, the bias thermal stabilization circuit 10 further includes a chip-level first transistor MP1, a chip-level second transistor MP2, a channel-level third transistor MP3, and a channel-level first transistor MP3. Four-transistor MP4.

The source of the first transistor MP1 is connected to the system power supply V _DD ; the drain of the first transistor MP1 is grounded through the first constant current source 101 ; the gate of the first transistor MP1 is connected to the drain of the first transistor MP1 .

The source of the second transistor MP2 is connected to the system power supply V _DD ; the drain of the second transistor MP2 is grounded through the second constant current source 102 ; the gate of the second transistor MP2 is connected to the drain of the second transistor MP2 and connected to the reference One terminal of the microbolometer R _b ; the other terminal of the reference microbolometer R _b is connected to the source of the third transistor MP3.

The drain of the third transistor MP3 is connected to the source of the fourth transistor MP4 and connected to the detection circuit 20 (for example, connected to the source of the fifth transistor MP5, as shown in FIG. 1 ); the gate of the third transistor MP3 is connected to to the gate of the fourth transistor MP4; the drain of the fourth transistor MP4 is grounded.

As shown in FIG. 1 , in some embodiments of the present invention, the detection circuit 20 includes a fifth transistor MP5, wherein the source of the fifth transistor MP5 is connected to the drain of the third transistor MP3 and connected to the integration circuit 30 (for example, connected to to the negative input of the operational amplifier of the integrating circuit 30, as shown in Figure 1); the drain of the fifth transistor MP5 is connected to one end of the detection microbolometer R _s , and the gate of the fifth transistor MP5 is connected to the bias Set the voltage V _fid ; the other end of the detection microbolometer R _s is grounded.

In some embodiments of the present invention, the detection circuit 20 may further include a switch S1, and the source of the fifth transistor MP5 is connected to the drain of the third transistor MP3 and the integration circuit 30 through the switch S1.

In the embodiment of the present invention, the integration circuit 30 may be an integration circuit commonly used in the art, for example, as shown in FIG. 1 , which will not be repeated here.

The working principle of the circuit of the embodiment of the present invention will be briefly described below.

For example, in the embodiment shown in FIG. 1 , the bias voltage V _eb generated by the current mirror structure of the chip-level PMOS transistor MP1 provides input to bias the gates of the PMOS transistors MP3 and MP4 of the thermal stabilization circuit 10 . The source level of MP3 is connected to the channel-level reference microbolometer Rb, and the other end of the reference microbolometer Rb is connected to the bias voltage V _SK generated by the chip-level PMOS transistor PM2 current mirror structure. The drain of MP4 is connected to ground. When the scanning is neutral and the detection circuit 20 is not connected, the channel-level reference microbolometer R _b , MP3 and MP4 form a complete circuit, and the current flowing through the drain of MP3 is I _BIAS . During the scanning period, the detection circuit 20 is connected to the bias thermal stabilization circuit 10. Due to the negative feedback amplification structure of the operational amplifier in the integrating circuit 30, the virtual short condition is satisfied, and the positive and negative input terminal voltages of the operational amplifier are equal. Therefore, when the detection circuit 20 is connected to the bias thermal stabilization circuit 10, the drain terminal voltage of MP3 is equal to the positive input terminal voltage V _ref of the integrator. Since MP4 is a PMOS transistor, when the gate-source voltage V _GS of the PMOS transistor is less than or equal to the threshold voltage V _th , the PMOS transistor is turned on to generate a drain-source current _ID . Taking the proper positive input terminal voltage V _ref of the integrator and the chip-level bias voltage V _eb , the drain-source voltage V _GS =V _G ?V _S =V _ref ?V _eb satisfies V _ref ?V _eb >V _th , that is, When the detection circuit 20 is connected to the bias thermal stabilization circuit 10, MP2 is turned off due to V _ref −V _eb >V _th . Taking an appropriate width-to-length ratio of MP2 can make the current flowing through the drain terminal of MP3 remain unchanged at I _bias .

In the circuit of the embodiment of the present invention, the reference microbolometer R _b flowing through the channel level and the current I _bias of the PMOS transistor MP3 are kept constant, so that the obtained integrated current I _int is only related to the pixel level detection microbolometer The bolometer R _s is related, that is:

I _int =I _BIAS –I _s =b–alpha×ΔT _scene (1)

In formula (1), b is a constant, I _s is the current flowing through the detection microbolometer R _s , alpha represents the temperature coefficient of the microbolometer, ΔT _scene represents the detection microbolometer R caused by infrared radiation _s temperature change. .

It can be seen from equation (1) that since the integrated current I _int has nothing to do with the bias heat of the channel-level reference microbolometer R _b , the final integrated output voltage V _out is obtained as:

In formula (2), V _ref is the reference voltage, t _int is the integration time, and C _int is the capacitance value of the integration capacitor in the integration circuit 30 . It can be seen that the obtained integrated output voltage V _out is only related to the radiation temperature, microbolometer and circuit parameter characteristics, and has nothing to do with the bias heat.

It can be seen that the present invention utilizes a method of providing a stable current branch for the channel-level microbolometer R _b to obtain a stable bias heat, so that the bias heat of the microbolometer does not change with time, thereby making the microbolometer The resistance change of the meter is only related to the intensity of the incident infrared radiation absorbed by it, which improves the output accuracy of the uncooled infrared focal plane readout circuit.

For example, FIG. 2 and FIG. 3 respectively show the simulation diagrams of the output voltage of the conventional readout circuit and the readout circuit according to the embodiment of the present invention with the target temperature at different substrate temperatures. It can be seen that the bias heat of the readout circuit of the embodiment of the present invention is more stable than that of the conventional readout circuit.

It can be seen that the readout circuit of the embodiment of the present invention provides a stable current path for the reference microbolometer, realizes the stability of bias heat, greatly improves the uniformity and reliability of the overall circuit, and greatly improves the reliability of the circuit. High pressure resistance and adaptability to the environment.

The present invention has been described above through specific examples, but the present invention is not limited to these specific examples. Those skilled in the art should understand that various modifications, equivalent replacements, changes, etc. can also be made to the present invention. As long as these changes do not deviate from the spirit of the present invention, they should all be within the protection scope of the present invention. In addition, "one embodiment" described in many places above represents different embodiments, and of course all or part of them may be combined in one embodiment.

Claims (4)

1. A readout circuit of an uncooled infrared focal plane array detector, characterized in that it comprises: a bias thermal stabilization circuit (10) comprising a channel-level reference microbolometer (R _b ) and providing _a constant bias current; A detection circuit (20) connected to the pixel-level detection _{microbolometer} (Rs) and the bias thermal stabilization circuit (10), and based on the reference microbolometer (R _b ) and said detection microbolometer (R _s ) generate a detection output signal; An integration circuit (30), the integration circuit (30) is connected to the detection circuit (20) and integrates the detection output signal of the detection circuit (20) to obtain an output signal. 2. The readout circuit according to claim 1, characterized in that, the bias thermal stabilization circuit (10) further comprises a chip-level first transistor (MP1), a chip-level second transistor (MP2), a channel The third transistor (MP3) of the stage and the fourth transistor (MP4) of the channel stage, where: The source of the first transistor (MP1) is connected to the system power supply (V _DD ), the drain of the first transistor (MP1) is grounded through the first constant current source (101), and the first transistor (MP1) the gate of is connected to the drain of the first transistor (MP1); The source of the second transistor (MP2) is connected to the system power supply (V _DD ), the drain of the second transistor (MP2) is grounded through the second constant current source (102), and the second transistor (MP2) the gate of is connected to the drain of said second transistor (MP2) and to one terminal of said reference microbolometer (R _b ); The other end of said reference microbolometer ( _Rb ) is connected to the source of said third transistor (MP3); The drain of the third transistor (MP3) is connected to the source of the fourth transistor (MP4) and to the detection circuit (20), the gate of the third transistor (MP3) is connected to the the gate of the fourth transistor (MP4); The drain of the fourth transistor ( MP4 ) is grounded. 3. The circuit according to claim 1 or 2, characterized in that the detection circuit (20) comprises a fifth transistor (MP5), wherein: The source of the fifth transistor (MP5) is connected to the drain of the third transistor (MP3) and to the integrating circuit (30), the drain of the fifth transistor (MP5) is connected to the Probing one terminal of the microbolometer (R _s ), the gate of said fifth transistor (MP5) is connected to a bias voltage (V _fid ); The other end of the detection microbolometer (R _s ) is grounded. 4. The circuit according to claim 3, characterized in that the source of the fifth transistor (MP5) is connected to the drain of the third transistor (MP3) and the integrating circuit ( 30).