The Design Of The Data Sampling System In Electro-optic Sampling

In Chapter 1, 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 must be 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.The design of preamplifier mainly focuses on lowering the noise of preamplifier, the key point of which is to choose the proper input device. In Chapter 2, 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...