Application Of Optical Receiver System Based On The Electro-optical Measuring

Photoelectric measurement technique is the traditional optical technology and modern electronic and computer technology closely linked to a new high technology, is to obtain optical information-extraction or on the backs of other information (eg, temperature, sound, electrical, biological) an important means. Use electro-optical measuring method is to modulation of the optical carrier useful signal transfer, and optical signal and signal conversion. In this paper, the study is aimed at integrated circuits fluorescent measurement system of the receiving part of the photoelectric applied research. The system needs to measure the optical signal is very weak ( pAtonA order), Therefore light detector and preamplifier have very high demands. How to improve the signal-to-noise ratio and improve the accuracy of the detection system is a key area of our research objectives. Furthermore, in order to achieve the intelligence system and equipment, Click on the photoelectric signal digital processing is the content of our study. This paper mainly for the following studies :Firstly,the sources of the noises of Electro-optic sampling system and the properties of photodiode detector are discussed. The noises of the circuit can be sorted into two groups: one comes from the objects being detected and the interior of the detecting system, namely narrow sense noise, which includes resistance thermal noise, dark current noise, low frequency noise and etc. Narrow sense noise can only be lowered down but never be eliminated completely. Other kinds of noises come from the environment, which differ from the narrow sense noise by their property of being regular and emerging periodically or instantly, which can be eliminated by some means.In this experiment, a PIN photodiode is used, which has high sensitivity of light detection and good frequency response. Since the output current ranges from hundreds of pA to tens of nA, the first-order current-voltage conversion mustbe conducted to enlarge the voltage signal to the required level before the final display. In order to achieve this purpose, a low noise preamplifier is designed, which has not only the function of current-voltage conversion and adjustable voltage gain mentioned above, but also the function of filtering circuit,adder and voltage follower.Secondly ,We noise preamplifier and the study . The design of preamplifier mainly focuses on lowering the noise of preamplifier, the key point of which is to choose the proper input device. The integrate operation amplifier is chosen as the amplifying device. The input bias current and open-loop input resistance of the integrate operation amplifier are two factors which effect the feeble current-voltage conversion. The input bias current of the integrate operation amplifier is the base current, which affects the amplifier by that the output value is not zero even though the input value is zero. Ideally, it's often supposed that the open-loop resistance of the operation amplifier is infinite, which means that the input part of the amplifier is open. However practically, every amplifier has its limited input resistance which effects the accuracy of the current-voltage conversion result, results in that the factual voltage is slightly less than the ideal voltage or the needed voltage. In order to solve these two problems, we selected an integrate operation amplifier with field-effect transistor (FET) as the input, which has a very high input resistance, about 10 8 ~1013? , and a feeble input bias current.The structure of the selected operation amplifier with the FET as the input is very simple. By connecting a feedback resistance between input part and output part of the operation amplifier, we can get the transimpedance or parallel negative feedback amplifier, which fulfill the function of current-voltage conversion. In real circuit, some measures of protective circuit and floating techniques are adopted. The negative feedback of the voltage parallel amplifier has many necessary effects on the whole circuit, including enhancing the stability, improving the nonlinearity, reduce the distortion and lowering the noise of the amplifier circuit. It can also decrease the usefuloutput signal and the noise proportionally. If the input signal is increased to make the output signal same with the signal without feedback, noise will be decreased with the same proportion. However, the negative feedback only has the rejection function to the noise coming from the interior of the amplifier system and has no effect to the noise outside of the system. we set out in detail the levels preamplifier circuit diagram, and the corresponding experimental results, in the paper.Finally, we study the measurement of the electro-optical signal processing and digital virtual show. Virtual instruments usually combines the hardware of the computer with the outside circuit to meet the request of some apparatus. Virtual instruments often take the form of data acquisition cards inserting into the computer. Furthermore, correspondent software must be designed in order to fulfill some factual functions such as the information exchange, data transporting, reading, storing, signal displaying, printing and etc.In the experiment, Call Library Function of LabVIEW is used to call the dynamic linking library(DLL)of USB chip, through which, the connection between the hardware and software is achieved. By setting up the buffer and index, the signals coming from USB are collected and then reverted into factual analog signals through some mathematical algorithms and displayed. These signals can be printed, stored, read, and processed of peak-peak, max.-minimum, period and frequency detection on virtual oscillograph.