Background technology
Photodiode circuit is widely used in the fields such as laser ranging, rays safety detection apparatus, motion control, analytical instrument, biologic medical, optical communication, military affairs, Aero-Space, optical communication.Wherein, the photodiode circuit generally adopted in pulse type laser range finding field comprises photodiode mutual conductance amplifying circuit, as shown in Figure 1, the most basic photodiode mutual conductance amplifying circuit mainly comprises operational amplifier U11, photodiode LD1 and resistance R11 and electric capacity C11.But this circuit exports and has a direct current biasing, and as shown in Figure 2, this direct current biasing that is to say ground unrest, and it is caused by the input bias current of the natural light of co-wavelength (bias light), photodiode dark current and trsanscondutance amplifier.Due in laser distance measuring system based on the decision level of flight time often very low (about 200mV), this direct current biasing can affect decision level, therefore in the range measurement system of reality, this ground unrest is needed to eliminate, allow when not having pulse signal, the output of photodiode mutual conductance amplifying circuit is 0.
The maximum photodiode circuit can eliminating ground unrest of current application as shown in Figure 3, this circuit adds analog to digital converter (ADC) on the basis of basic photodiode mutual conductance amplifying circuit, digital to analog converter (DAC), single-chip microcomputer (MCU), the elements such as impact damper (BUFFER) and resistance R12, its principle gathers the output voltage of photodiode mutual conductance amplifying circuit by analog to digital converter and is sent in single-chip microcomputer, needing the voltage value compensated to give digital to analog converter after carrying out filtering scheduling algorithm by single-chip microcomputer, then the input of photodiode mutual conductance amplifying circuit is exported to, thus reach the object of the output voltage zeroing of photodiode mutual conductance amplifying circuit.
But there is following shortcoming in this circuit of prior art:
1, owing to employing digital element (single-chip microcomputer), cause additionally adding noise, the finding range of photodiode can be made to diminish, thus can make that the distance of range finding is remarkable must shorten;
2, add more extra element, cause cost compare high;
3, the Area comparison of integrated circuit is large, is unfavorable for the miniaturization of product.
Summary of the invention
The present invention is directed to exist in the photodiode circuit that prior art uses additionally add that noise causes finding range to diminish, element is more causes that cost is higher, integrated circuit area causes more greatly being unfavorable for the technical matterss such as product miniaturization, propose a kind ofly significantly to reduce noise, cost is lower, integrated circuit area the is less photodiode circuit eliminated based on ground unrest.
A kind of photodiode circuit eliminated based on ground unrest that the present invention proposes, it comprises photodiode mutual conductance amplification module, amplifier integrator module, filtration module, described filtration module is connected to the output terminal of described photodiode mutual conductance amplification module and the input end of described amplifier integrator module, and the output terminal of described amplifier integrator module is connected to the input end of described photodiode mutual conductance amplification module.
Concrete, described amplifier integrator module comprises the first operational amplifier, the first electric capacity, the first resistance and the second resistance; Between the inverting input that described first electric capacity is connected to described first operational amplifier and output terminal; Described first resistance one end is connected to the inverting input of described first operational amplifier, other end ground connection; Described second resistance one end be connected to described first operational amplifier output terminal, the other end is connected to the input end of described photodiode mutual conductance amplification module; The in-phase input end of described first operational amplifier is connected to the output terminal of described filtration module.
Concrete, described photodiode mutual conductance amplification module comprises photodiode, the second operational amplifier, the 3rd resistance and the second electric capacity; The negative electrode access bias voltage of described photodiode, anode is connected to the inverting input of described second operational amplifier; Between the inverting input being connected to described second operational amplifier after described 3rd resistance and the second Capacitance parallel connection and output terminal; The inverting input of described second operational amplifier also connects with described second resistance, output terminal also with the connecting of described filtration module.
Concrete, described filtration module comprises the 3rd electric capacity and the 4th resistance; Described 3rd electric capacity one end ground connection, the other end connects with the in-phase input end of described first operational amplifier and one end of described 4th resistance respectively, and the other end of described 4th resistance connects with the output terminal of described second operational amplifier.
Concrete, described photodiode is avalanche photodide.
Accordingly, the present invention is corresponding proposes a kind of laser distance measuring system, and it comprises above-mentioned arbitrary photodiode circuit eliminated based on ground unrest.
Beneficial effect: a kind of photodiode circuit eliminated based on ground unrest that the present invention proposes, which employs amplifier integrator module, integration can be carried out to the direct current biasing that photodiode mutual conductance amplification module exports, and send back to the input end of photodiode mutual conductance amplification module, to reach the object of DC-offset correction.Meanwhile, the filtration module in the present invention can filter out the high frequency noise (high frequency noise is pulse signal itself mainly) of photodiode mutual conductance amplification module output terminal, thus makes amplifier integrator not by the impact of this high frequency noise.
In the present invention, amplifier integrator module can only use operational amplifier, electric capacity and resistance, filtering circuit can only use electric capacity and resistance, and whole circuit does not use digital element, can not bring additional noise, largely can improve the signal to noise ratio (S/N ratio) of circuit, increase finding range; Simultaneously owing to only using operational amplifier, resistance and electric capacity, cost hinge structure reduces many, and integrated circuit area also greatly reduces, thus is conducive to the miniaturization of product.
Embodiment
For the ease of it will be appreciated by those skilled in the art that the present invention is described further below in conjunction with accompanying drawing and embodiment.
Refer to Fig. 4, a kind of photodiode circuit embodiment eliminated based on ground unrest that the present invention proposes, it comprises photodiode mutual conductance amplification module, amplifier integrator module, filtration module, described filtration module is connected to the output terminal of described photodiode mutual conductance amplification module and the input end of described amplifier integrator module, and the output terminal of described amplifier integrator module is connected to the input end of described photodiode mutual conductance amplification module.
A kind of photodiode circuit eliminated based on ground unrest that the present embodiment proposes, which employs amplifier integrator module, integration can be carried out to the direct current biasing that photodiode mutual conductance amplification module exports, and send back to the input end of photodiode mutual conductance amplification module, to reach the object of DC-offset correction.Meanwhile, the filtration module in the present embodiment can filter out the high frequency noise (high frequency noise is pulse signal itself mainly) of photodiode mutual conductance amplification module output terminal, thus makes amplifier integrator not by the impact of this high frequency noise.
In the present embodiment, amplifier integrator module can only use operational amplifier, electric capacity and resistance, filtering circuit can only use electric capacity and resistance, and whole circuit does not use digital element, can not bring additional noise, largely can improve the signal to noise ratio (S/N ratio) of circuit, increase finding range; Simultaneously owing to only using operational amplifier, resistance and electric capacity, cost hinge structure reduces many, and integrated circuit area also greatly reduces, thus is conducive to the miniaturization of product.
In order to realize the object of the present embodiment better, the present embodiment has done optimal design for described amplifier integrator module, concrete, and described amplifier integrator module comprises the first operational amplifier U1, the first electric capacity C1, the first resistance R1 and the second resistance R2; Between the inverting input that described first electric capacity C1 is connected to described first operational amplifier U1 and output terminal; Described first resistance R1 mono-end is connected to the inverting input of described first operational amplifier U1, other end ground connection; Described second resistance R2 mono-end be connected to described first operational amplifier U1 output terminal, the other end is connected to the input end of described photodiode mutual conductance amplification module; The in-phase input end of described first operational amplifier U1 is connected to the output terminal of described filtration module.
In the present embodiment, described photodiode mutual conductance amplification module can be the most basic photodiode mutual conductance amplifying circuit, concrete, and it comprises photodiode LD, the second operational amplifier U2, the 3rd resistance R3 and the second electric capacity C2; The negative electrode access bias voltage of described photodiode LD, anode is connected to the inverting input of described second operational amplifier U2; Between the inverting input being connected to described second operational amplifier U2 after described 3rd resistance R3 and the second electric capacity C2 parallel connection and output terminal; The inverting input of described second operational amplifier U2 also connects with described second resistance R2, output terminal also with the connecting of described filtration module.
In order to realize the object of the present embodiment further better, filtration module described in the present embodiment can be common RC low-pass filter, concrete, and the filtration module of the present embodiment comprises the 3rd electric capacity C3 and the 4th resistance R4; Described 3rd electric capacity C3 one end ground connection, the other end connects with the in-phase input end of described first operational amplifier U1 and one end of described 4th resistance R4 respectively, and the other end of described 4th resistance R4 connects with the output terminal of described second operational amplifier U2.
In the present embodiment, described photodiode LD can be avalanche photodide.
Based on the particular circuit configurations of above-mentioned amplifier integrator module, photodiode mutual conductance amplification module and filtration module, below carry out circuit analysis, to be described in further detail the process realizing the present embodiment object.
Please continue to refer to Fig. 4, in the present embodiment, the first operational amplifier U1 and the second operational amplifier U2 is used as desirable operational amplifier.Owing to employing this energy-storage travelling wave tube of electric capacity, therefore following employing S domain analysis method, the variable of capitalization all represents S territory function, and the variable of small letter is real number, and resistance and condenser symbol all represent real number.
In order to simplify calculating, the second electric capacity C2 (filter capacitor) is not counted in derivation.First electric capacity C1 (integrating capacitor) is reduced to C in derivation, and the resistance of the first resistance R1, the second resistance R2, the 3rd resistance R3 and the 4th resistance R4 is designated as R respectively
1, R
2, R
3and R
4, then:
The output voltage V of photodiode mutual conductance amplification module
ofor:
V
o=-I
i·R
3
The electric current flowing through the first electric capacity C1 equals the electric current flowing through the first resistance R1, this electric current I
1for:
The output voltage V of amplifier integrator module
0mfor:
Offset current (flowing through the electric current of the second resistance R2) I
mfor:
The input current I of the second operational amplifier U2
i, photocurrent I
pdwith offset current I
malso have following relation:
I
i=I
pd-I
m
Will above two containing I
mequation merge, cancellation I
m:
Background photo current is made to be step input signal, then I
pdcan be expressed as:
Wherein, i
pdbe the actual electric current out of photodiode LD, substitute into I above
iformula, and simplify obtain:
Ask granny rag Lars inverse transformation can obtain the input current i of the second operational amplifier U2
itime-domain expression:
Time-domain expression can be seen thus, and the actual electric current being input to the second operational amplifier U2 inverting input successively decreases with the trend of the negative exponent of natural logarithm, finally can be substantially equal to 0.Because all circuit components are not desirable, so this electric current can be finally zero.So the output of mutual conductance is also zero.Select suitable resistance and electric capacity, this decline trend can be allowed faster.
From above conclusion of deriving, no matter bias light is how many, the output of described photodiode mutual conductance amplification module finally all can be adjusted to 0 automatically.
Meanwhile, from the circuit result of reality, also demonstrate the feasibility of the present embodiment scheme, refer to Fig. 5, Fig. 5 is the result after the electrical block diagram of Fig. 4 in the present embodiment adopts MATLAB to emulate.According to the configuration of each resistance in Fig. 5 left side and electric capacity, if there is ground unrest electric current (the i.e. I of 100uA
pd=100uA), this Circuits System can allow the VD of photodiode mutual conductance amplification module drop to 0.1V, circuit successful within the time of 0.53ms.Parameter adjustment can be carried out as required, to obtain the attenuation characteristic wanted.
Accordingly, the invention allows for a kind of laser distance measuring system embodiment, it comprises above-mentioned based on arbitrary circuit structure scheme in the photodiode circuit embodiment of ground unrest elimination, its beneficial effect please refer to the introduction of the above-mentioned photodiode circuit embodiment based on ground unrest elimination, repeats no more here.
The above embodiment only have expressed several embodiment of the present invention, and it describes comparatively concrete and detailed, but therefore can not be interpreted as the restriction to the scope of the claims of the present invention.It should be pointed out that for the person of ordinary skill of the art, without departing from the inventive concept of the premise, can also make some distortion and improvement, these all belong to protection scope of the present invention.Therefore, the protection domain of patent of the present invention should be as the criterion with claims.