Research On Virtual Function Generator Based On USB Interface In Photoelectron Test System

Under the traction of photoelectron test and the target of photoelectron test system, and with the direction of instrument development ,the article studys and manufactures a virtual function generator based on USB interface.Virtual instrument is an automation instrument system based on computers. It is the combination of fresh PC technology, advanced test techniques and powerful software.With the development of photoelectron and computer technology, photoelectron test system is very important in testing and debugging photoelectron equipments. Virtual machine acts as an important role in photoelectron test system. Different kinds of virtual instruments can be controlled, managed and data processed by computer. They are highly automated, who provide a powerful method of testing and debugging on photoelectron equipments developing and photoelectron experiment curriculum teaching. Virtual machine has the characteristic of convenient, fast, accurate and flexible.The virtual function generator in the article communicates with the computer by USB interface .In end of PC application software is implemented under delphi IDE,and the development of the USB driver under Win2000 is aided by Driver Studio 3.1. In the end of instrument three kinds of waveforms are developed by the chip MAX038, the changing of the frequency and the duty and the choice of the waveform which will be outputted are implemented by changing the corresponding pins' parameters,the high-resolution amplitude control is implemented by the voltage controlled gain amplifier--LMH6503, the high-resolution frequency control is implemented by the feedback of the frequency which is measured by cymometer.The characteristics of the virtue function generator are:1. It implements the interface between virtue machine and computer by USB, which is more convenient and has faster speed.2. It uses CPLD instead of 74 series chips to implement the control logics. It can be modified easily and is much flexible.3. The high-resolution frequency control is implemented by the feedback of the cymometer which is programmed in CPLD, Frequencies will be very stable.4. The waveform is generated by MAX038. It is very convenient to adjust the frequency, duty cycle and offset voltage of the waveform by changing parameters of the corresponding pins of the chip.5. It implements the high-resolution amplitude control of the waveform with the voltage controlled gain amplifier~LMH6503, which makes the range of the adjusting is±10 V,resolution is up to 2.5mV.6. It defined the control instructions referring to SCPI rules, which makes second-turn development much easier.7. The development of the USB driver under Win2000 is aided by Driver Studio 3.1, which is driver-development oriented software made by Compuwar Corporation.Compared with the GFG-8210 analog function generator in all indexes, the output of our equipment has reached the same level. What is more, ours has some advantages by virtual machine which analog function generator doesn't have. The output of our function generator has reach the requirement of ordinary equipments in the range of 0.1Hz~10MHz and -10V-10V. It can be safely used in teaching and researching of the labs.