A weak signal amplification and shaping circuit applied to a blood analyzer

Abstract

The present invention relates to the field of pulse technology, and discloses a weak signal amplification and shaping circuit applied to a blood analyzer. The signal in the blood analyzer enters the optoelectronic signal input terminal. The first infinite gain multiple feedback low-pass filter amplifies the pre-stage signal and filters out unnecessary high-frequency interference signals at the same time. The high-pass filter filters out low-frequency noise interference. The second infinite gain multiple feedback low-pass filter amplifies the pre-stage signal and filters out unnecessary high-frequency interference signals at the same time. The negative feedback amplification and rectification module amplifies the signal and shapes the waveform. At the same time, the channel is switched to perform different amplification gains. The voltage follower ensures that the signal is output to the next stage as losslessly as possible during transmission. The protection circuit output terminal adjusts the threshold voltage, so as to have the function of a band-pass filter, reduce noise, and can extract and amplify weak pulse signals with strong anti-interference ability.

Description

Technical Field

[0001] The present invention relates to the field of pulse technology, and particularly to a weak signal amplification and shaping circuit applied to a blood analyzer. Background Art

[0002] A blood analyzer can provide blood cell counting and classification in clinical tests, providing data support for doctors' diagnoses. The five-classification of blood cells refers to the five-classification examination of white blood cells. When performing a blood routine test, white blood cells are divided into five categories, and the number of each category of white blood cells is counted. These five categories of white blood cells include neutrophils, eosinophils, basophils, monocytes, and lymphocytes. Due to the different sizes and complexities of these 5 types of white blood cells, based on flow cytometry technology, the sheath flow wraps the cell suspension and passes through a light illumination area at a constant speed. In the light illumination area, the cells are irradiated by a laser. Due to the inconsistent sizes, shapes, and complexities of the cells, the intensity of the scattered light is different at different angles. By collecting the intensity signals of the scattered light of the cells in the sheath flow irradiated by the laser at various angles, the characteristics of the cells can be summarized. However, since the pulse signal is relatively weak. For various weak signals to be measured, they are generally converted into a low voltage by a corresponding sensor and then amplified in amplitude by an amplifier.

[0003] Since the signal to be measured is weak, the background noise of the sensor, the inherent noise of the amplifier circuit and the measuring instrument, and the external interference noise are often much larger than the amplitude of the useful signal. The process of amplifying the measured signal also amplifies the noise, and some additional noise will inevitably be added, such as the internal inherent noise and external interference noise of the amplifier. Therefore, the weak signal cannot be detected only by amplification. Only by increasing the amplitude of the weak signal under the condition of effectively suppressing the noise can the useful signal be extracted. In addition to classifying white blood cells, a blood analyzer can also test reticulocytes and related parameters. Since the reticulocyte signal is weaker than the white blood cell signal and is more difficult to test. The commonly used method is to set a set of amplification multiples at the front stage to simultaneously amplify the reticulocyte signal and the white blood cell classification signal. However, the adjustable margin of this method is insufficient. If the optical path system changes slightly later, for white blood cell classification, the signal amplification multiple is too large, but for the reticulocyte signal, this amplification multiple is still not enough. Summary of the Invention

[0004] The purpose of the present invention is to provide a weak signal amplification and shaping circuit applied to a blood analyzer, aiming to extract and amplify weak pulse signals and improve the anti-interference ability.

[0005] To achieve the above object, the present invention provides a weak signal amplification and shaping circuit applied to a blood analyzer, which includes a photoelectric signal input terminal, an IV conversion circuit connected to the photoelectric signal input terminal, a first infinite gain multiple feedback low-pass filter connected to the IV conversion circuit, a high-pass filter module connected to the first infinite gain multiple feedback low-pass filter, a second infinite gain multiple feedback low-pass filter connected to the high-pass filter module, a negative feedback amplification and rectification module connected to the second infinite gain multiple feedback low-pass filter, a voltage follower connected to the negative feedback amplification and rectification module, and a protection circuit output terminal connected to the voltage follower.

[0006] Among them, the IV conversion circuit includes a first amplifier, a first resistor, and a first capacitor. The photoelectric signal input terminal is connected to the inverting input terminal of the first amplifier, the non-inverting input terminal of the first amplifier is grounded, the first resistor is connected in parallel between the inverting input terminal and the output terminal of the first amplifier, and the first capacitor is connected in parallel between the inverting input terminal and the output terminal of the first amplifier.

[0007] Among them, the first infinite gain multiple feedback low-pass filter includes a second amplifier, a second resistor, a third resistor, a fourth resistor, a fourth capacitor, and a fifth capacitor. The second resistor is connected to the output terminal of the first amplifier, one end of the third resistor is connected to the second resistor, the other end of the third resistor is connected to the inverting input terminal of the second amplifier, the fourth capacitor is connected between the non-inverting input terminal of the second amplifier and the end of the second resistor close to the third resistor, the fourth resistor is connected between the output terminal of the second amplifier and the end of the second resistor close to the third resistor, and the fifth capacitor is connected between the inverting input terminal and the output terminal of the second amplifier.

[0008] Among them, the high-pass filter module includes an eighth capacitor and a fifth resistor. One end of the eighth capacitor is connected to the output terminal of the second amplifier, and the other end of the eighth capacitor is connected to the fifth resistor.

[0009] Among them, the second infinite gain multiple feedback low-pass filter includes a third amplifier, a sixth resistor, a seventh resistor, an eighth resistor, a ninth capacitor, and a tenth capacitor. One end of the sixth resistor is connected to the eighth capacitor, the other end of the sixth resistor is connected to the eighth resistor, the inverting input terminal of the third amplifier is connected to the eighth resistor, one end of the ninth capacitor is connected to the end of the sixth resistor close to the eighth resistor, the other end of the ninth capacitor is grounded, one end of the seventh resistor is connected to the end of the sixth resistor close to the eighth resistor, the other end of the seventh resistor is connected to the output terminal of the third amplifier, and the tenth capacitor is connected in parallel between the inverting input terminal and the output terminal of the third amplifier.

[0010] Among them, the negative feedback amplification and rectification module includes a fourth amplifier, a two-way analog switch, a ninth resistor, a tenth resistor, an eleventh resistor, a second diode, and a third diode. The ninth resistor is connected to the output end of the third amplifier. The inverting input end of the fourth amplifier is connected to the ninth resistor. The positive electrode of the second diode is connected to the inverting input end of the fourth amplifier. The negative electrode of the second diode is connected to the output end of the fourth amplifier. The positive electrode of the third diode is connected to the output end of the fourth amplifier. The tenth resistor is connected to the negative electrode of the third diode. The eleventh resistor is connected to the negative electrode of the third diode. The two-way analog switch is connected to the inverting input end of the fourth amplifier and is arranged on one side of the tenth resistor and the eleventh resistor.

[0011] Among them, the voltage follower includes a seventh amplifier, a twelfth resistor, and an eleventh capacitor. The twelfth resistor is connected to the negative electrode of the third diode. The non-inverting input end of the seventh amplifier is connected to the twelfth resistor. The inverting input end of the seventh amplifier is connected to the output end of the seventh amplifier.

[0012] Among them, the output end of the protection circuit includes a voltage stabilizer, an eighth amplifier, a thirteenth resistor, a fourteenth resistor, a fifteenth resistor, a sixteenth resistor, a seventeenth resistor, an eighteenth resistor, a nineteenth resistor, a first triode, a second triode, and a fourteenth capacitor. The nineteenth resistor is connected to the output end of the seventh amplifier. The emitter of the second triode is connected to the nineteenth resistor. The collector of the second triode is grounded. The base of the second triode is connected to the eighteenth resistor. The output end of the eighth amplifier is connected to the eighteenth resistor. The emitter of the first triode is connected to the inverting input end of the eighth amplifier. The collector of the first triode is grounded. One end of the seventeenth resistor is connected to the base of the first triode. The other end of the seventeenth resistor is connected to the output end of the eighth amplifier. One end of the sixteenth resistor is connected to the inverting input end of the eighth amplifier. The other end of the sixteenth resistor is connected to the power supply end of the eighth amplifier. One end of the thirteenth resistor is connected to the power supply end of the eighth amplifier. The other end of the thirteenth resistor is connected to the non-inverting input end of the eighth amplifier. The fourteenth resistor is connected to the thirteenth resistor. One end of the fifteenth resistor is connected to the fourteenth resistor. The other end of the fifteenth resistor is grounded. One end of the fourteenth capacitor is connected to the non-inverting input end of the eighth amplifier. The other end of the fourteenth capacitor is grounded. The voltage stabilizer is arranged at both ends of the fourteenth resistor and the fifteenth resistor.

[0013] A weak signal amplification and shaping circuit applied to a blood analyzer. In the blood analyzer, the optical channel needs to amplify the three angular signals of the sheath flow to obtain (S1, S2, S3). Since the three signals belong to different angles, their respective amplification factors are adjusted according to actual needs. Here, only one channel will be described. Specifically, the signal to be processed has a center frequency of 120Khz and a bandwidth of 100khz. The photoelectric sensor inputs a signal at the nA level. The photoelectric sensor in the blood analyzer generates a current after being irradiated by light, and the current I is input from the photoelectric signal input terminal. s_in The first infinite gain multiple feedback low-pass filter is used to amplify the pre-stage signal and filter out the unwanted high-frequency interference signals at the same time. The function of the high-pass filter is to filter out the low-frequency noise interference. The function of the second infinite gain multiple feedback low-pass filter is to amplify the pre-stage signal and filter out the unwanted high-frequency interference signals at the same time. The negative feedback amplification and rectification module can amplify the signal and also shape the waveform. At the same time, it can also switch channels to suit different amplification gains. The voltage follower can prevent waveform overshoot or self-excitation oscillation of the amplification circuit during actual use. The output end of the protection circuit can adjust the threshold voltage, thus having the function of a band-pass filter to reduce noise. At the same time, it has a protection output circuit and a protection voltage setting, which can extract and amplify weak pulse signals and has strong anti-interference ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0015] Figure 1 FIG. is a module structure diagram of a weak signal amplification and shaping circuit applied to a blood analyzer according to the present invention;

[0016] Figure 2 FIG. is a detailed circuit diagram of a weak signal amplification and shaping circuit applied to a blood analyzer according to the present invention;

[0017] Figure 3 FIG. is a structure diagram of the IV conversion circuit according to the present invention;

[0018] Figure 4 FIG. is a structure diagram of the first infinite gain multiple feedback low-pass filter;

[0019] Figure 5 FIG. is a structure diagram of the high-pass filter module;

[0020] Figure 6 is the structural diagram of a second infinite gain multiple feedback low-pass filter;

[0021] Figure 7 is the structural diagram of a negative feedback amplification and rectification module;

[0022] Figure 8 is the structural diagram of a voltage follower;

[0023] Figure 9 is the structural diagram of the output end of a protection circuit;

[0024] Figure 10 is the schematic diagram of waveform shaping;

[0025] Figure 11 is the pulse diagram of the present invention.

[0026] 1 - Photoelectric signal input end, 2 - IV conversion circuit, 3 - First infinite gain multiple feedback low-pass filter, 4 - High-pass filter module, 5 - Second infinite gain multiple feedback low-pass filter, 6 - Negative feedback amplification and rectification module, 7 - Voltage follower, 8 - Output end of protection circuit, U1-A - First amplifier, R1 - First resistor, C1 - First capacitor, U2-A - Second amplifier, R2 - Second resistor, R3 - Third resistor, R4 - Fourth resistor, C4 - Fourth capacitor, C5 - Fifth capacitor, U2-B - Third amplifier, R6 - Sixth resistor, R7 - Seventh resistor, R8 - Eighth resistor, C9 - Ninth capacitor, C10 - Tenth capacitor, U4-B - Fourth amplifier, U3-B - Two-way analog switch, R9 - Ninth resistor, R10 - Tenth resistor, R11 - Eleventh resistor, D2 - Second diode, D3 - Third diode, U4-A - Seventh amplifier, R12 - Twelfth resistor, U5 - Voltage stabilizer, U6-A - Eighth amplifier, R13 - Thirteenth resistor, R14 - Fourteenth resistor, R15 - Fifteenth resistor, R16 - Sixteenth resistor, R17 - Seventeenth resistor, R18 - Eighteenth resistor, R19 - Nineteenth resistor, Q1 - First triode, Q2 - Second triode, C8 - Eighth capacitor, R5 - Fifth resistor. Specific embodiments

[0027] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0028] Please refer to Figures 1 to 9 , the present invention provides a weak signal amplification and shaping circuit applied to a blood analyzer:

[0029] It includes a photoelectric signal input terminal 1, an IV conversion circuit 2 connected to the photoelectric signal input terminal 1, a first infinite gain multiple feedback low-pass filter 3 connected to the IV conversion circuit 2, a high-pass filter module 4 connected to the first infinite gain multiple feedback low-pass filter 3, a second infinite gain multiple feedback low-pass filter 5 connected to the high-pass filter module 4, a negative feedback amplification and rectification module 6 connected to the second infinite gain multiple feedback low-pass filter 5, a voltage follower 7 connected to the negative feedback amplification and rectification module 6, and a protection circuit output terminal 8 connected to the voltage follower 7.

[0030] In this embodiment, in a blood analyzer, the optical channel needs to amplify and obtain the three-angle signals (S1, S2, S3) of the sheath flow. Since the three signals belong to different angles and their respective amplification factors are adjusted according to actual needs, only one of the channels is described here. Specifically, the signal center frequency to be processed is 120Khz and the bandwidth is 100khz. The photoelectric sensor inputs a signal with a current level of nA.

[0031] In the blood analyzer, after being irradiated by light, the photoelectric sensor generates a current, and the current I is input from the photoelectric signal input terminal 1. s_in The first infinite gain multiple feedback low-pass filter 3 is used to amplify the pre-stage signal and simultaneously filter out the unwanted high-frequency interference signals. The function of the high-pass filter is to filter out the low-frequency noise interference. The function of the second infinite gain multiple feedback low-pass filter 5 is to amplify the pre-stage signal and simultaneously filter out the unwanted high-frequency interference signals. The negative feedback amplification and rectification module 6 can amplify the signal and also shape the waveform. At the same time, it can also switch channels to suit different amplification gains. The voltage follower 7 can prevent waveform overshoot or self-excited oscillation of the amplifier circuit during actual use. The protection circuit output terminal 8 can adjust the threshold voltage, thus having the function of a band-pass filter, reducing noise, and at the same time having a protection output circuit and a protection voltage setting, which can extract and amplify weak pulse signals and has strong anti-interference ability.

[0032] Further, the IV conversion circuit 2 includes a first amplifier U1-A, a first resistor R1, and a first capacitor C1. The photoelectric signal input terminal 1 is connected to the inverting input terminal of the first amplifier U1-A. The non-inverting input terminal of the first amplifier U1-A is grounded. The first resistor R1 is connected in parallel between the inverting input terminal and the output terminal of the first amplifier U1-A. The first capacitor C1 is connected in parallel between the inverting input terminal and the output terminal of the first amplifier U1-A.

[0033] In this embodiment, the output voltage U = -I s_in*R1. The capacitor C1 has a phase-advancing effect. In the basic I-V conversion circuit, due to the input parasitic capacitance causing phase lag, the circuit becomes prone to oscillation, so phase compensation is required.

[0034] Furthermore, the first infinite-gain multiple-feedback low-pass filter 3 includes a second amplifier U2-A, a second resistor R2, a third resistor R3, a fourth resistor R4, a fourth capacitor C4, and a fifth capacitor C5. The second resistor R2 is connected to the output terminal of the first amplifier U1-A. One end of the third resistor R3 is connected to the second resistor R2, and the other end of the third resistor R3 is connected to the inverting input terminal of the second amplifier U2-A. The fourth capacitor C4 is connected to the non-inverting input terminal of the second amplifier U2-A and the end of the second resistor R2 close to the third resistor R3. The fourth resistor R4 is connected to the output terminal of the second amplifier U2-A and the end of the second resistor R2 close to the third resistor R3. The fifth capacitor C5 is connected to the inverting input terminal and the output terminal of the second amplifier U2-A.

[0035] In this embodiment, the function of the module is to amplify the pre-stage signal and simultaneously filter out unwanted high-frequency interference signals. The gain G1 = -R4 / R2. The natural angular frequency Low-pass filter cut-off frequency

[0036] Furthermore, the high-pass filter module 4 includes an eighth capacitor C8 and a fifth resistor R5. One end of the eighth capacitor C8 is connected to the output terminal of the second amplifier U2-A, and the other end of the eighth capacitor C8 is connected to the fifth resistor R5.

[0037] In this embodiment, the cut-off frequency The function of the module is to filter out low-frequency noise interference.

[0038] Further, the second infinite gain multiple feedback low-pass filter 5 includes a third amplifier U2-B, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth capacitor C9, and a tenth capacitor C10. One end of the sixth resistor R6 is connected to the eighth capacitor C8, the other end of the sixth resistor R6 is connected to the eighth resistor R8, the inverting input terminal of the third amplifier U2-B is connected to the eighth resistor R8, one end of the ninth capacitor C9 is connected to the end of the sixth resistor R6 close to the eighth resistor R8, the other end of the ninth capacitor C9 is grounded, one end of the seventh resistor R7 is connected to the end of the sixth resistor R6 close to the eighth resistor R8, the other end of the seventh resistor R7 is connected to the output terminal of the third amplifier U2-B, and the tenth capacitor C10 is connected in parallel between the inverting input terminal and the output terminal of the third amplifier U2-B.

[0039] In this embodiment, the function of the second infinite gain multiple feedback low-pass filter 5 is to amplify the pre-stage signal and filter out the unwanted high-frequency interference signals at the same time. The gain G2 = -R7 / R6. The natural angular frequency Low-pass filter cut-off frequency Combined with the high-pass filter of the previous module, this module forms a band-pass filter circuit, which suppresses signals outside the frequencies f1 to f2.

[0040] Further, the negative feedback amplification and rectification module 6 includes a fourth amplifier U4-B, a two-way analog switch U3-B, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a second diode D2, and a third diode D3. The ninth resistor R9 is connected to the output terminal of the third amplifier U2-B, the inverting input terminal of the fourth amplifier U4-B is connected to the ninth resistor R9, the positive electrode of the second diode D2 is connected to the inverting input terminal of the fourth amplifier U4-B, the negative electrode of the second diode D2 is connected to the output terminal of the fourth amplifier U4-B, the positive electrode of the third diode D3 is connected to the output terminal of the fourth amplifier U4-B, the tenth resistor R10 is connected to the negative electrode of the third diode D3, the eleventh resistor R11 is connected to the negative electrode of the third diode D3, and the two-way analog switch U3-B is connected to the inverting input terminal of the fourth amplifier U4-B and is arranged on one side of the tenth resistor R10 and the eleventh resistor R11.

[0041] In this embodiment, in a hematology analyzer, in order to save costs, white blood cells and reticulocytes often share the same channel. However, the optical signal received when measuring reticulocytes is much weaker than that of white blood cells, which makes it difficult to find a compromise point. For example, if an operational amplifier is used to amplify the collected signal so that the system can identify it and adjust the reticulocyte signal to an appropriate size, the signal of white blood cells will be amplified too much at this time. If the white blood cell signal is adjusted to an appropriate size, the reticulocyte signal will be too small. Therefore, a two-way analog switch U3-B is used here to switch according to the needs of the measurement signal. The gain G3 = -R10 / R9 or G3 = -R11 / R9. The combination of diodes D2 and D3 realizes waveform rectification. Therefore, in addition to amplifying the signal, this module also needs to shape the waveform. However, this module no longer performs filtering because, due to inconsistent feedback resistors, when the filtering frequency is adjusted and then switched to another channel, the filtering parameters will change. The waveform shaping principle is as follows Figure 10 , during the positive half-cycle (0 to t1) of the input signal, D2 is turned on and D3 is turned off, and the circuit is equivalent to a voltage follower 7: Before D2 and D3 are turned on, the circuit is in an open-loop state with a very large voltage amplification factor. At this time (during the positive half-wave input of the input signal), a tiny input signal makes the input terminal of the amplifier become negative. Diode D2 is forward-biased and turned on (equivalent to a short circuit), and D3 is reverse-biased and cut off (equivalent to an open circuit), forming the mode of voltage follower 7. Since the non-inverting terminal is grounded, the circuit becomes a voltage follower 7 following the ground level, and the output terminal can still maintain zero potential. During the negative half-cycle (t1 to t2) of the input signal, D2 is turned off and D3 is turned on, and the circuit is equivalent to an inverter. During the negative half-wave of the input signal (before D2 and D3 are turned on), a tiny input signal makes the output terminal become positive. Diode D2 is reverse-biased and cut off, and D3 is forward-biased and turned on, forming the circuit mode of an inverting (amplifying) amplifier, and the negative half-wave signal is inverted and output.

[0042] Furthermore, the voltage follower 7 includes a seventh amplifier U4-A and a twelfth resistor R12. The twelfth resistor R12 is connected to the negative electrode of the third diode D3. The positive input terminal of the seventh amplifier U4-A is connected to the twelfth resistor R12, and the negative input terminal of the seventh amplifier U4-A is connected to the output terminal of the seventh amplifier U4-A.

[0043] In this embodiment, the output impedance of the voltage amplifier is generally relatively high, usually ranging from a few kiloohms to dozens of kiloohms. If the input impedance of the subsequent stage is relatively small, a considerable part of the signal will be lost in the output resistance of the previous stage. At this time, the voltage follower 7 is required to buffer it, playing a role of connecting the preceding and the following. The twelfth resistor R12 and the eleventh capacitor C11 are reserved for use. To prevent waveform overshoot or self-excited oscillation of the amplifier circuit during actual use, corresponding values can be set according to actual use conditions or they can be left unconnected.

[0044] Further, the output terminal 8 of the protection circuit includes a voltage regulator U5, an eighth amplifier U6-A, a thirteenth resistor R13, a fourteenth resistor R14, a fifteenth resistor R15, a sixteenth resistor R16, a seventeenth resistor R17, an eighteenth resistor R18, a nineteenth resistor R19, a first triode Q1, a second triode Q2, and a fourteenth capacitor C14. The nineteenth resistor R19 is connected to the output terminal of the seventh amplifier U4-A. The emitter of the second triode Q2 is connected to the nineteenth resistor R19. The collector of the second triode Q2 is grounded. The base of the second triode Q2 is connected to the eighteenth resistor R18. The output terminal of the eighth amplifier U6-A is connected to the eighteenth resistor R18. The emitter of the first triode Q1 is connected to the inverting input terminal of the eighth amplifier U6-A. The collector of the first triode Q1 is grounded. One end of the seventeenth resistor R17 is connected to the base of the first triode Q1. The other end of the seventeenth resistor R17 is connected to the output terminal of the eighth amplifier U6-A. One end of the sixteenth resistor R16 is connected to the inverting input terminal of the eighth amplifier U6-A. The other end of the sixteenth resistor R16 is connected to the power supply terminal of the eighth amplifier U6-A. One end of the thirteenth resistor R13 is connected to the power supply terminal of the eighth amplifier U6-A. The other end of the thirteenth resistor R13 is connected to the non-inverting input terminal of the eighth amplifier U6-A. The fourteenth resistor R14 is connected to the thirteenth resistor R13. One end of the fifteenth resistor R15 is connected to the fourteenth resistor R14. The other end of the fifteenth resistor R15 is grounded. One end of the fourteenth capacitor is connected to the non-inverting input terminal of the eighth amplifier U6-A. The other end of the fourteenth capacitor is grounded. The voltage regulator U5 is provided across the fourteenth resistor R14 and the fifteenth resistor R15.

[0045] In this embodiment, by the voltage regulator U5 according to the proportional relationship of different values of the fourteenth resistor R14 and the fifteenth resistor R15, the threshold voltage V we want can be obtained. linit . The calculation formula is as follows: V limit = V ref (1 + R14 / R15) + Iref *R14, where V ref and I ref can be obtained by referring to the chip data sheet. The specific principle is that the positive terminal input voltage of the eighth amplifier U6-A is V limit , then under the feedback effect, the negative terminal input angular voltage will also reach V limit , and at this time the output of the operational amplifier is also V limit , otherwise there will be current passing through the seventeenth resistor R17 and the entire circuit will not be balanced. Assume the output voltage is V s_out . When V s_out >V limit , the conduction voltage drop of the second triode Q2 is zero, the second triode Q2 is turned off again, the voltage rises, and finally when it reaches equilibrium, V s_out = V limit , thus achieving the protection of the subsequent circuit. For example Figure 11 of the three pulse signals, when the signal is greater than V limit , it will be clamped at V limit .

[0046] For example Figure 11 as shown, the 4 pulses at time T, the pulse signals at t3~t4 and t5~t6, because the amplitude exceeds V limit , so they are limited at V limit , protecting the subsequent circuit.

[0047] The above-disclosed is only a preferred embodiment of the present invention. Of course, the scope of the rights of the present invention cannot be limited by this. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A weak signal amplification and shaping circuit applied to a blood analyzer, characterized in that, it includes a photoelectric signal input terminal, an IV conversion circuit connected to the photoelectric signal input terminal, a first infinite gain multiple feedback low-pass filter connected to the IV conversion circuit, a high-pass filter module connected to the first infinite gain multiple feedback low-pass filter, a second infinite gain multiple feedback low-pass filter connected to the high-pass filter module, a negative feedback amplification and rectification module connected to the second infinite gain multiple feedback low-pass filter, a voltage follower connected to the negative feedback amplification and rectification module, and a protection circuit output terminal connected to the voltage follower; The protection circuit output terminal includes a voltage stabilizer, an eighth operational amplifier, a thirteenth resistor - a nineteenth resistor, a first triode, a second triode, and a fourteenth capacitor. One end of the nineteenth resistor is connected to the output terminal of the voltage follower, the emitter of the second triode is connected to the other end of the nineteenth resistor, the collector of the second triode is grounded, the base of the second triode is connected to one end of the eighteenth resistor, the output terminal of the eighth operational amplifier is connected to the other end of the eighteenth resistor and one end of the seventeenth resistor, the other end of the seventeenth resistor is connected to the base of the first triode, the emitter of the first triode is connected to the inverting input terminal of the eighth operational amplifier and one end of the sixteenth resistor, the other end of the sixteenth resistor is connected to the power supply terminal of the eighth operational amplifier, the collector of the first triode is grounded, the non-inverting input terminal of the eighth operational amplifier is connected to the thirteenth resistor, the fourteenth resistor, the fourteenth capacitor, and one end of the negative electrode of the voltage stabilizer. The other end of the thirteenth resistor is connected to the power supply terminal of the eighth operational amplifier, the other end of the fourteenth resistor is connected to the control terminal of the voltage stabilizer and one end of the fifteenth resistor, and the other end of the fifteenth resistor, the positive electrode of the voltage stabilizer, and the other end of the fourteenth capacitor are respectively grounded.

2. The weak signal amplification and shaping circuit applied to a blood analyzer according to claim 1, characterized in that, the IV conversion circuit includes a first operational amplifier, a first resistor, and a first capacitor. The photoelectric signal input terminal is connected to the inverting input terminal of the first operational amplifier, the non-inverting input terminal of the first operational amplifier is grounded, the first resistor is connected in parallel with the inverting input terminal and the output terminal of the first operational amplifier, and the first capacitor is connected in parallel with the inverting input terminal and the output terminal of the first operational amplifier.

3. The weak signal amplification and shaping circuit applied to a blood analyzer according to claim 2, characterized in that, The first infinite gain multiple feedback low-pass filter includes a second operational amplifier, a second resistor, a third resistor, a fourth resistor, a fourth capacitor, and a fifth capacitor. One end of the second resistor is connected to the output terminal of the first operational amplifier, and the other end of the second resistor is connected to one ends of the third resistor, the fourth resistor, and the fourth capacitor. The other end of the third resistor is connected to the inverting input terminal of the second operational amplifier, and the other end of the fourth capacitor is connected to the non-inverting input terminal of the second operational amplifier. The other end of the fourth resistor is connected to the output terminal of the second operational amplifier. The other end of the fourth capacitor is also grounded. One end of the fifth capacitor is connected to the inverting input terminal of the second operational amplifier, and the other end of the fifth capacitor is connected to the output terminal of the second operational amplifier.

4. The weak signal amplification and shaping circuit applied to a blood analyzer according to claim 3, wherein The high-pass filter module includes an eighth capacitor and a fifth resistor. One end of the eighth capacitor is connected to the output terminal of the second operational amplifier, and the other end of the eighth capacitor is connected to one end of the fifth resistor. The other end of the fifth resistor is grounded.

5. The weak signal amplification and shaping circuit applied to a blood analyzer according to claim 4, wherein The second infinite gain multiple feedback low-pass filter includes a third operational amplifier, a sixth resistor, a seventh resistor, an eighth resistor, a ninth capacitor, and a tenth capacitor. One end of the sixth resistor is connected to the other end of the eighth capacitor, and the other end of the sixth resistor is connected to one ends of the eighth resistor, the seventh resistor, and the ninth capacitor. The inverting input terminal of the third operational amplifier is connected to the other end of the eighth resistor. The non-inverting input terminal of the third operational amplifier is grounded. The other end of the ninth capacitor is grounded. The other end of the seventh resistor is connected to the output terminal of the third operational amplifier. The tenth capacitor is connected in parallel between the inverting input terminal and the output terminal of the third operational amplifier.

6. The weak signal amplification and shaping circuit applied to a blood analyzer according to claim 5, wherein The negative feedback amplification and rectification module includes a fourth operational amplifier, a two-way analog switch, a ninth resistor, a tenth resistor, an eleventh resistor, a second diode, and a third diode. One end of the ninth resistor is connected to the output terminal of the third operational amplifier, and the other end of the ninth resistor is connected to the input terminal of the two-way analog switch, the positive electrode of the second diode, and the inverting input terminal of the fourth operational amplifier. The negative electrode of the second diode is connected to the output terminal of the fourth operational amplifier. The positive electrode of the third diode is connected to the output terminal of the fourth operational amplifier. The negative electrode of the third diode is connected to one ends of the tenth resistor and the eleventh resistor. The other end of the tenth resistor is connected to the first output terminal of the two-way analog switch. The other end of the eleventh resistor is connected to the second output terminal of the two-way analog switch. The non-inverting output terminal of the fourth operational amplifier is grounded.

7. The weak signal amplification and shaping circuit applied to a blood analyzer according to claim 6, wherein The voltage follower includes a seventh operational amplifier, a twelfth resistor, and an eleventh capacitor. One end of the twelfth resistor is connected to the negative electrode of the third diode. The positive input terminal of the seventh operational amplifier is connected to the other end of the twelfth resistor and one end of the eleventh capacitor. The negative input terminal of the seventh operational amplifier is connected to the output terminal of the seventh operational amplifier, and the other end of the eleventh capacitor is grounded.

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