CN103837512B - It is applied to the HVB high voltage bias circuit of the avalanche diode APD that week fluorescent is measured - Google Patents

Abstract

The invention discloses a high-voltage bias circuit of an avalanche diode APD applied to weak fluorescence measurement, including a control signal unit, a control signal conditioning unit, a temperature-free amplification unit, an output buffer unit and a feedback unit, and the control signal is processed through the control signal conditioning unit. The signal is conditioned, and then amplified by the temperature-free amplifying unit to obtain the required bias voltage value, and then the output buffer unit and the feedback unit are used to control the stability of the output. The invention adopts the method of mutual coupling of temperature drift coefficients between components, which eliminates the problem of voltage drift with temperature in the previous high-voltage bias circuit, and has the advantages of high-voltage output with high temperature stability, and the output does not decrease with the increase of the signal. Meet the high-voltage bias requirements for APD operation.

Description

High Voltage Bias Circuit of Avalanche Diode APD Applied in Weak Fluorescence Measurement

technical field

The invention belongs to the field of biomedical detection, and in particular relates to a high-voltage bias circuit of an avalanche diode APD used in weak fluorescence measurement.

Background technique

In the field of biomedicine, fluorescence technology is often used for qualitative and quantitative measurement of substances, research on immune proteins on the cell surface, and determination of DNA content. Because the fluorescence intensity is very weak, and APD (avalanche diode) can achieve avalanche multiplication, and has high quantum efficiency and low price, it is often used to test the fluorescence intensity. The normal operation of APD requires a high-voltage bias of tens to hundreds of volts, and its multiplication factor changes with the increase of the voltage. Therefore, in order to ensure the accuracy of the measurement results, a stable bias voltage needs to be provided to ensure that the APD can perform fluorescence accurately. A measure of strength.

APD has been widely used in the field of optical communication, such as US patents US5625181A, US6031219A, US6643472B1, etc., but its application requirements in the biomedical field are very different. In optical communication, optoelectronic receivers usually only need to distinguish the difference between '0' (none) and '1' (yes) of optical signals, while the research on fluorescence in the field of biomedicine does not only stop at '0' (none) and '1' '(there are) stages, but to distinguish more than two, or even 8 different intensity signals (flow cytometry applications), and to ensure good linearity, so for the stability of the bias voltage output by the APD The requirements are more stringent.

The optical receiving system described in US Patent US5625181A is mainly composed of three parts: SELF-BIASSECTION (self-bias part), APDBIASCONTROLLOOPSECTION (avalanche diode bias control loop part), and TEMPERATURE COMPENSATIONSECTION (temperature compensation part), which has two problems:

1. The bias voltage output will decrease as the optical signal increases. In the self-bias part, when the optical signal increases, the current flowing through the APD will increase, and the voltage drop formed by the current through R1 will increase (usually R1 is also relatively large by about 1M), which will cause the bias of the APD Set the voltage down;

2. The bias voltage will change with temperature drift. In the part of the avalanche diode bias control loop, when the temperature drifts, the inherent temperature drift of the PN junction of TR1 is 2mv/°C, that is, the voltage (Vbe) between the base and emitter of TR1 has a temperature drift of 2mv/°C, The total temperature drift can be calculated with the following formula: , assuming that R1/R4 is equal to 50, and the temperature drifts by 2°C, the bias voltage will drift by 200mV. Such bias voltage drift will cause the gain of the APD to change, thus affecting the accuracy of the results. Although it has a temperature compensation part, the temperature drift coefficient of TR1 is only an approximate value, and it is unrealistic to perform detailed experiments on each module to compensate, so TR1 is usually only used to compensate APD gain caused by temperature changes The change.

Contents of the invention

The purpose of the present invention is to overcome the problem that the bias voltage output of the traditional APD high-voltage bias circuit will decrease with the increase of the optical signal and the bias voltage will change with the drift of the temperature, so that the APD can be more accurately Perform bioluminescent tests.

In order to achieve the above-mentioned technical purpose and achieve the above-mentioned technical effect, the present invention is realized through the following technical solutions:

The high-voltage bias circuit of the avalanche diode APD applied to weak fluorescence measurement includes a control signal unit, a control signal conditioning unit, a temperature-free amplification unit, an output buffer unit, and a feedback unit. The control signal output by the control signal unit passes through the After the signal conditioning unit is adjusted, the output signal is suitable for a specific APD tube. The output signal is amplified by the temperature-free amplification unit to output a high-voltage electrical signal. After the electrical signal passes through the output buffer unit, it outputs the bias of the APD tube. Voltage, the output voltage of the output buffer unit is input to the signal conditioning unit through the feedback unit to output a feedback signal to form a feedback loop, wherein:

The drift-free amplifying unit mainly includes two complementary PNP transistors and a first NPN transistor, wherein the emitter of the PNP transistor is connected to the base of the first NPN transistor;

Further, the control signal unit includes a temperature measurement chip, the signal conditioning unit mainly includes an adder, the output end of the temperature measurement chip is connected to the inverting input end of the adder through an adjustable resistor R22, and the adder The inverting input end of the device is also connected to the control signal terminal Vctrl, and the output end of the adder is also connected to the base stage of the PNP transistor;

Preferably, the value of the adjustable resistor R22 is adjusted according to the temperature coefficient of the avalanche diode, so as to compensate the change of the gain of the avalanche diode caused by the temperature change.

Further, the output buffer unit includes a second NPN transistor, the base of the second NPN transistor is connected to the collector of the first NPN transistor, and the feedback unit includes a voltage dividing resistor R51 and a resistor R52 One end of the resistor R52 is connected to the emitter of the second NPN transistor, the other end is respectively connected to the positive input end of the adder and the resistor R51, and the other end of the resistor R51 is grounded.

Preferably, the resistor R51 can be formed by connecting two or more resistors in parallel.

Preferably, the resistor R52 may be composed of two resistors or multiple resistors connected in series.

The beneficial effects of the present invention are:

The invention adopts the method of mutual coupling of temperature drift coefficients between components, which eliminates the problem that the voltage of the high-voltage bias circuit drifts with temperature in the past, and can realize high-voltage output with high temperature stability, and meet the high-voltage bias demand when the APD is working .

Description of drawings

Fig. 1 is a system composition block diagram of the present invention;

Fig. 2 is the bias circuit diagram of the present invention, wherein, for convenience of description, resistance 21, adjustable resistance 22, resistance 23, resistance 32, resistance 34, resistance 35, resistance 51 and resistance 52 correspond to R21, R22, R23, R32, R34, R35, R51 and R52.

detailed description

The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

Referring to Figure 1, the high-voltage bias circuit of an avalanche diode APD applied to weak fluorescence measurement includes a control signal unit 1, a control signal conditioning unit 2, a temperature-free amplification unit 3, an output buffer unit 4 and a feedback unit 5;

Referring to Fig. 2, the amplifying unit 3 without temperature drift mainly includes two complementary PNP transistors 31 and a first NPN transistor 33, wherein the emitter of the PNP transistor 31 is connected to the first NPN transistor 33, and connected to high level Vcc through resistor 32, the collector of the PNP transistor 31 is grounded, the emitter of the first NPN transistor 33 is grounded through resistor 35, and its collector is connected to resistor 34. High level HV;

The control signal unit 1 includes a temperature measurement chip 11, the signal conditioning unit 2 mainly includes an adder 24, the output end of the temperature measurement chip 11 is connected to the inverting input end of the adder 24 through an adjustable resistor 22, The inverting input end of described adder 24 also connects the output end of control signal terminal Vctrl and adder 24 by resistance 21 and resistance 23 respectively, and the output end of described adder 24 also connects the base stage of described PNP type transistor 31 ;

The output buffer unit 4 includes a second NPN transistor 41, the base of the second NPN transistor 41 is connected to the collector of the first NPN transistor 33, and the collector of the second NPN transistor 41 is connected to a high level HV, the feedback unit 5 includes a voltage dividing resistor 51 and a resistor 52, one end of the resistor 52 is connected to the emitter of the second NPN transistor 41, and the other end is respectively connected to the positive electrode of the adder 24. To the input terminal and the resistor 51, the other end of the resistor 51 is grounded.

Continuing to refer to Fig. 2, the proportional coefficient k1=R23/R21 of the control signal of the setting adder 24 in the present embodiment, the ratio k2=R23/R22 of the output signal of the temperature measurement chip of the adder 24, the gain of the amplification unit 3 without temperature drift Coefficient M=R34/R35, feedback unit 5 feedback coefficient β=R51/(R51+R52), the output APD bias voltage is Vapd, the input control signal Vctrl, the temperature measurement chip output signal Vt, the offset value b (refers to the triode 31 and the mismatch value between the triode 33 and the common influencing factors of the Vbe of the triode 41), so the output and input have the following relationship:

(1-1)

Among the three items in the above formula (1-1), the first item is the gain of the control signal, the second item is the output signal gain of the temperature measurement chip, the third item is the intercept, and the first two items are the voltage value output by the circuit at 0.

According to the above formula (1-1), the actual circuit can be built according to the demand, the example is as follows:

Assuming that the range of Vctrl is 0 to 3V, an APD tube from Hamamatsu is used, its temperature coefficient k=0.65V/℃, the high voltage HV is 200V, and the voltage range to be adjusted is from 70V to 150V. The output of the temperature measurement chip is 10mV/℃, and the output is 250mV when the room temperature is 25 degrees.

Build the circuit according to the circuit structure given in Figure 2, and determine the parameters according to the formula as follows:

1. Determine the control signal gain. The swing of the control signal 0 to 3v should correspond to the required voltage regulation range of 70V to 150V, so ;

2. Determine the output signal gain of the temperature measurement chip. In order to realize the temperature coefficient compensation of the APD tube, the output signal of the temperature measurement chip needs to be able to compensate the APD tube temperature coefficient k=0.65V/℃, so , combined with step 1, we can get, ;

3. Determine the minimum output voltage signal. The minimum output voltage signal is 70V. Considering that at room temperature, the output voltage value of the temperature measurement signal is not 0, take it as 25°C, that is, the output is 0.25V, Vh=200V so ;

4. Calculate the values of k1, k2, and β. Assuming that the gain of the amplifying unit without temperature drift in step 3 is M=50 (the problem of power consumption considered is R34=1MΩ, R35=20kΩ), when M is determined, b is a constant, and its influence is only on the calculated voltage value A constant is superimposed on it, and it is set to 5V according to experience, then , combined with And step 1, the formula in step 2 is calculated to get , , ;

5. Determine the resistance value. Take R23=10kΩ, then R21=5.17kΩ, R22=2.12kΩ,

Take R52=10.2M, then R51=70.6kΩ,

R32 is 1kΩ for the current limiting resistor, Vcc is 5V;

6. Fine-tuning. In order to reduce the cost, the resistance value that does not have strict requirements on the gain is adjusted to the standard value, take R21=5.1kΩ, R52 is two 5.1MΩ in series, and R51 is taken as 68kΩ. R22 is taken as an adjustable resistor of 5kΩ. Transistor model 31 uses MPSA92, 33 and 41 uses MPSA42. Depend on Recalculated as R22=2.212, control signal gain .

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (4)

1. The high-voltage bias circuit of the avalanche diode APD applied to weak fluorescence measurement, including the control signal unit (1), the control signal conditioning unit (2), the temperature-free amplification unit (3) and the output buffer unit (4) connected in sequence ), the output end of the output buffer unit (4) is connected to the input end of the control signal conditioning unit (2) through a feedback unit (5), wherein: The temperature-free amplifying unit (3) mainly includes a PNP transistor (31) and a first NPN transistor (33), wherein the PNP transistor (31) and the first NPN transistor (33) are complementary, wherein the The emitter of the PNP transistor (31) is connected to the base of the first NPN transistor (33); The control signal unit (1) includes a temperature measurement chip (11), the control signal conditioning unit (2) mainly includes an adder (24), and the output terminal of the temperature measurement chip (11) is passed through an adjustable resistor (22 ) is connected to the inverting input of the adder (24), the inverting input of the adder (24) is also connected to the control signal terminal Vctrl, and the output of the adder (24) is also connected to the PNP type The base of the triode (31); The output buffer unit (4) includes a second NPN transistor (41), the base of the second NPN transistor (41) is connected to the collector of the first NPN transistor (33), and the feedback The unit (5) includes a voltage dividing resistor (51) and a feedback resistor (52), one end of the feedback resistor (52) is connected to the emitter of the second NPN transistor (41), and the other end is respectively connected to the adder (24) positive input terminal and the voltage dividing resistor (51), and the other end of the voltage dividing resistor (51) is grounded. 2. The high-voltage bias circuit of the avalanche diode APD applied to weak fluorescence measurement according to claim 1, characterized in that, the value of the adjustable resistor (22) is adjusted according to the temperature coefficient of the avalanche diode, and the compensation changes with temperature Changes in the gain of the avalanche diode caused by the change. 3. The high-voltage bias circuit of an avalanche diode (APD) applied to weak fluorescence measurement according to claim 1, characterized in that, the voltage dividing resistor (51) is composed of two or more resistors connected in parallel. 4. The high-voltage bias circuit of an avalanche diode APD applied to weak fluorescence measurement according to claim 1, characterized in that, the feedback resistor (52) is composed of two resistors or a plurality of resistors connected in series.