CN214793487U - Photoelectric detection circuit with high signal-to-noise ratio - Google Patents

Abstract

The utility model belongs to the technical field of the circuit, specifically disclose a high SNR photoelectric detection circuit, including photodiode D, photodiode D passes through the wire and connects operational amplifier's reverse input end, operational amplifier's forward input end ground connection, feedback compensation network is constituteed to parallelly connected feedback resistance Rf and feedback resistance Cf between operational amplifier's reverse input end and the output, operational amplifier output series resistance R and resistance R, electric capacity C is connected with the one end that resistance R is connected, electric capacity C ground connection, electric capacity C is connected to resistance R's the other end, electric capacity C ground connection. The utility model has the advantages of low output noise, good linearity and simple structure.

Description

Photoelectric detection circuit with high signal-to-noise ratio

Technical Field

The utility model belongs to the circuit field specifically discloses a high SNR photoelectric detection circuit.

Background

In recent years, a photoelectric detection technology taking a photoelectric detector as a core has been widely applied to the fields of military affairs, industry, agriculture, environmental science, medical treatment, aerospace and the like, and the technology mainly realizes detection and analysis of an original optical signal by converting an optical signal irradiated on a photodiode into a corresponding optical current signal and further optimizing subsequent circuits such as current-voltage signal conversion, amplification, filtering and the like.

The photodiode detection device is often used as a core device in a photoelectric detection system because of its advantages of fast response, high sensitivity, good linearity, low noise, etc., but if the detected optical signal is weak, an external photoelectric amplification circuit is often required, and due to the difference of the device chip type selection and the designed circuit structure, the electrical signal at the output end is easily affected by impedance shunt and various noise superposition in the detection circuit, so that the linear responsivity of the photoelectric detection circuit is often deteriorated or the signal-to-noise ratio is too low. The circuit structure form in weak photoelectric detection and the related requirements of device chip selection are analyzed in detail from two aspects of linear response and noise characteristics of the photoelectric detection circuit of the photodiode.

Disclosure of Invention

In view of this, the present invention provides a photoelectric detection circuit with high signal-to-noise ratio to solve the problems of the prior art.

In order to achieve the above object, the utility model provides a high SNR photoelectric detection circuit, including photodiode D, photodiode D passes through the wire and connects operational amplifier's reverse input end, operational amplifier's forward input end ground connection, feedback compensation network is constituteed to parallelly connected feedback resistance Rf and feedback resistance Cf between operational amplifier's reverse input end and the output, operational amplifier output series resistance R and resistance R, electric capacity C is connected to the one end that resistance R and resistance R are connected, electric capacity C ground connection, electric capacity C is connected to resistance R's the other end, electric capacity C ground connection.

In the above technical solution, preferably, the operational amplifier is connected to an operating voltage, and the operating voltage and the ground are connected to a capacitor C of 100 nF.

In the foregoing technical solution, preferably, the photodiode D is an InGaAs photodiode

Compared with the prior art, the utility model discloses following beneficial effect has: the circuit takes a G12181-020K photoelectric detection device and an OPA858 low-noise high-gain operational amplifier chip as examples, related weak photoelectric detection circuits are designed and tested, and test results show that the designed circuit has the advantages of low output noise, good linearity and simple structure. In the test, the equivalent noise of the output end does not exceed 10mV actually, and the linear correlation degree of the weak light signal condensed by the lens reaches 0.99 within the low illumination range of 0.1-10 Lux.

Drawings

FIG. 1 is a schematic diagram of an equivalent detection circuit structure of an InGaAs photodiode;

FIG. 2 is a schematic diagram of a photodetection circuit of the photodiode;

FIG. 3 is a noise equivalent model of a photodiode photodetection circuit;

FIG. 4 is a schematic diagram of a design of a photodetection circuit;

FIG. 5 output noise of the photodetection circuit;

FIG. 6 output voltage versus light.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention more clearly understood, the present invention will be described in further detail with reference to the accompanying drawings and detailed description.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced in other ways than those specifically described herein, and the present invention is not limited to the specific embodiments disclosed below.

The high signal-to-noise ratio photodetection circuit shown in fig. 1-6 comprises a photodiode D9, a photodiode D9 is connected with the reverse input end of the operational amplifier 1 through a wire, the forward input end of the operational amplifier 1 is grounded, a feedback resistor Rf 3 and a feedback resistor Cf 4 are connected in parallel between the reverse input end and the output end of the operational amplifier 1 to form a feedback compensation network, the output end of the operational amplifier 1 is connected with a resistor R15 and a resistor R26 in series, one end of the resistor R26 connected with a resistor R15 is connected with a capacitor C18, the capacitor C18 is grounded, the other end of the resistor R26 is connected with a capacitor C27, and the capacitor C27 is grounded. The operational amplifier 1 is connected to an operating voltage which is connected to a capacitor C32 of 100 nF connected to ground. The photodiode D is an InGaAs photodiode.

In order to make the circuit more convincing, the development process and device model selection of the circuit will be described in detail through some noise analysis and noise test.

In various experiments or projects applying photodetection, for more accurate evaluation of the measured quantity, a photosensor is often required to have a good linear output response, i.e., a photo-generated current is converted into an output current input to an external load with as low loss as possible, and therefore, analysis of the linear response of the output of its photodetection circuit is particularly important. Theoretically, the photodiode structure can be equivalent to a form that a constant current source is connected in parallel with a shunt structure thereof, and light composed of photodiode detection devices can be combined with a photodiode detector SPICE (simulation program with integrated circuit emulation model) equivalent model

The electrical detection circuit is simplified to an equivalent model as shown in fig. 1. In the context of figure 1 of the drawings,

is an equivalent constant current source, D is the shunt resistance of the photodiode which is the equivalent ideal diode structure and the value of which is related to the size of the photodiode and is influenced by the temperature, the lower the temperature is, the smaller the junction area is,

the larger;

is a photodiode junction capacitance whose value is affected by an applied bias voltage and junction area, the larger the bias voltage, the smaller the junction area,

the smaller the size of the tube is,

its equivalent series resistance, its value is also related to its bias and structure;

，

respectively an equivalent load resistance and an equivalent load capacitance of the subsequent detection circuit.

When the applied optical signal is a weak low-frequency optical signal, the optical current will be changed into a weak direct current signal between several nanoamperes and several microamperes after being output by the photodetector, so that fig. 1 shows that

，

The shunting effect of (a) can be neglected. In FIG. 1, the current flowing through the equivalent ideal diode D and the parallel resistor

，

：

In the formula:

the reverse saturation current after biasing the photodiode, i.e. the dark current without illumination, has a value related to the junction area of the photodiode itself, and the smaller the junction area, the smaller the dark current

Smaller, q is the electronic quantity, k is the boltzmann constant;

is the voltage applied to the photodiode, A is a constant having a value equal to about 2

And if k/q is about 0.026V, the current on the load is increased

Can be expressed as:

therefore, in order to improve the linearity of the output end of the photodiode detection circuit, the following requirements are satisfied:

1) load connected to photodiode end

=0；

2) The photodiodes are selected to meet the requirements of dark current

Extremely small, parallel shunt resistance

Large series resistance

The smaller condition.

In order to detect as much as possible a weak photocurrent signal mixed in the detection circuit noise, it is essential to analyze the circuit noise characteristics. Through the analysis of the linear equivalent model of the photodiode detection circuit, the photodiode detection device receives the luminous flux signal and converts the luminous flux signal into an electric signal to be outputIn the process, the load at the output end of the photodiode is required to meet the requirement as much as possible

The output end of the detection circuit has good linear response only if the output end of the detection circuit has 0. Therefore, according to the "virtual short" characteristic of the input terminal when the operational amplifier circuit works normally, the photodiode can be connected across the positive and negative input terminals of the operational amplifier circuit, and the schematic diagram of the detection circuit is shown in fig. 2. In the context of figure 2, it is shown,

is a feedback resistor;

for feedback capacitance, connected in parallel at

Two ends can effectively prevent the diseases caused by

The self-excitation of the detection circuit caused by the overlarge phenomenon can reduce the bandwidth of the detection circuit and inhibit the noise interference. Fig. 3 shows an equivalent noise analysis model of the circuit structure.

Therefore, in order to improve the output signal-to-noise ratio, it is necessary to:

selecting shunt resistor in parallel

Large and output photocurrent

Also larger photodiode (

The choice is not easily too large, mainly because

Larger increases photodiode dark current);

2) selection inputTerminal voltage equivalent noise density

Current noise density

The operational amplifier chip has a smaller bandwidth gain product B;

3) feedback resistance of feedback loop

Feedback capacitor

Under the condition of not influencing the normal work of the circuit and meeting the circuit bandwidth, a larger value is required.

Through the analysis, the G12181-020K optical detection device of InGaAs photoelectric detection series of hamamatsu company is taken as an example, and is matched with a low-noise high-gain OPA858 operational amplifier chip to design a low-light-level detection circuit and perform related tests.

A schematic diagram of a photoelectric detection amplifying circuit designed by the selected device and chip is shown in FIG. 4 according to the equivalent linear response of the photoelectric detection circuit of the photodiode and the analysis result of the noise characteristic model.

In FIG. 4, the feedback resistor

3 and

form a feedback compensation network, the photoelectric current is output by 10 pins after being amplified, and then output by the amplifier

And

the passive second-order RC filter network further filters noise interference in the output electric signal. In fig. 4, the capacitor C32 at 100 nF of the operating voltage and ground terminal is a power filter capacitor;the capacitors connected to pins 1 and 2 of the chip are memory capacitors, and play a role in automatic zero stabilization.

An experimental board circuit is built according to the design principle diagram shown in fig. 4, and the output noise of the built circuit is tested by using an oscilloscope under the condition of no illumination, as shown in fig. 5. The test shows that the noise DC offset of the output end is about 2 mV, and the actual noise effective value does not exceed 10mV on average, which means that the sensitivity of the detection circuit can reach 10 mV.

In the low-illumination weak light environment, in order to fully collect weak light signals and eliminate the influence of uneven light irradiation on the experimental precision after the light irradiates the surface of the photoelectric device, the experiment enables the weak light signals to be detected to be firstly condensed by a lens, the effective photosurface of the photoelectric detector is vertically irradiated by the front side of the low-illumination light signals with the illumination intensity of 0.1-10 lux after condensation, and the measured illumination relation of the output end voltage and the input end is shown in fig. 6.

FIG. 6 shows that, for a weak optical signal with an illuminance of 0.1-10 lux (corresponding to a photocurrent of 5-500 nA at the output end of the detector), the linear correlation degree of the photoelectric detection circuit can reach 0.99, and the linear output response is good.

The design tests related weak photoelectric detection circuits, and test results show that the designed circuit has the advantages of low output noise, good linearity and simple structure. In the test, the equivalent noise of the output end does not exceed 10mV actually, and the linear correlation degree of the weak light signal condensed by the lens reaches 0.99 within the low illumination range of 0.1-10 Lux.

In the present invention, the terms "mounting", "connecting", "fixing" and the like are used in a broad sense, for example, "connecting" may be a fixed connection, a detachable connection, or an integral connection; may be directly connected or indirectly connected through an intermediate. The specific meaning of the above terms in the present invention can be understood according to specific situations by those skilled in the art.

In the description herein, the appearances of the phrase "one embodiment," "some embodiments," "a specific embodiment," or the like, are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the above embodiments, and that the principles of the present invention may be applied to any other embodiment without departing from the spirit and scope of the present invention. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (3)

1. The utility model provides a high SNR photoelectric detection circuit, includes photodiode D (9), its characterized in that, photodiode D (9) pass through the reverse input end of wire connection operational amplifier (1), the forward input end ground of operational amplifier (1), parallelly connected feedback resistance Rf (3) and feedback resistance Cf (4) constitute feedback compensation network between the reverse input end of operational amplifier (1) and the output, operational amplifier (1) output series resistance R1 (5) and resistance R2 (6), the one end that resistance R2 (6) and resistance R1 (5) are connected is connected electric capacity C1 (8), electric capacity C1 (8) ground connection, electric capacity C2 (7) are connected to the other end of resistance R2 (6), electric capacity C2 (7) ground connection.

2. A photodetection circuit with high snr according to claim 1, characterized in that the operational amplifier (1) is connected to an operating voltage, which is connected to a capacitor C3 (2) with 100 nF to ground.

3. The photodetection circuit with high signal-to-noise ratio according to claim 1, wherein the photodiode D is an InGaAs photodiode.

Images