ＢＪＴ參數(shù)測試儀中數(shù)控微電流源研究與實(shí)現(xiàn)

摘 要：對(duì)BJ參數(shù)測試儀中數(shù)控微電流源進(jìn)行研究與設(shè)計(jì)。系統(tǒng)采用owland電流泵構(gòu)成高精度V/I轉(zhuǎn)換器，V/I轉(zhuǎn)換器輸入為數(shù)/模轉(zhuǎn)換器的輸出電壓，微控制器通過改變輸入數(shù)/模轉(zhuǎn)換器的數(shù)字量實(shí)現(xiàn)對(duì)電流源輸出電流控制。對(duì)數(shù)控微電流源的工作原理做了定性和定量分析，并通過實(shí)驗(yàn)驗(yàn)證設(shè)計(jì)的正確性。該數(shù)控微電流源通過雙電阻反饋網(wǎng)絡(luò)構(gòu)成閉環(huán)控制系統(tǒng)，其輸出電流精度高、穩(wěn)定性好，具有良好的負(fù)載特性。

關(guān)鍵詞：BJ;微控制器;數(shù)控微電流源;閉環(huán)控制

Research and Realization of NC Micro[CD2]current ource in BJ Parametric est ystem

LIANG Wenhai

(Department of Physics and Electronic Engineering，ichuan Normal University，Chengdu，610068，China)

Abstract：he NC micro[CD2]current source of BJ parametric test system is researched and designedhe system consists of a high[CD2]precision V/I converters based on owland current pump，and the D/A output and the V/I input is connected，herefore the MCU can control the current[CD2]sources′ output by adjusting D/A dataQualitative and the quantitative analysis to the NC micro[CD2]current source′s principle are made，and the design accuracy through the experiment is confirmedhe NC micro[CD2]current source constituted the closed[CD2]loop control system through the double resistance feedback networkherefore，its output current precision is higher，the stability is good，and has good load characteristics

Keywords：BJ；MCU；NC micro[CD2]current source；close[CD2]loop control

在數(shù)字式BJ(Bipolar Junction ransistor，雙極面結(jié)型晶體管)參數(shù)測試系統(tǒng)中為了準(zhǔn)確測量交直流放大倍數(shù)、輸入/輸出特性曲線等特性參數(shù)，需要在被測三極管的基極加合適的偏置電壓，并且所加的偏置電壓根據(jù)測試的具體參數(shù)不同其大小要能程控變化；另一方面，小功率BJ的基極輸入電流較小，對(duì)其進(jìn)行取樣、處理過程中需要較大放大倍數(shù)的直流放大器，放大器設(shè)計(jì)較困難，而且零漂、干擾較大，會(huì)增大參數(shù)的測試誤差；在實(shí)際使用時(shí)有NPN型和PNP型BJ，所以要求電流源輸出是雙極性的。為此設(shè)計(jì)了滿足小功率BJ參數(shù)測試要求的雙極性高精度數(shù)控微電流源，預(yù)置電流直接送入被測三極管的基極，這樣就不需對(duì)基極電流進(jìn)行采樣，不但簡化了電路設(shè)計(jì)，而且減小了系統(tǒng)測試誤差。

1 數(shù)字式BJ參數(shù)測試原理

根據(jù)BJ主要特性參數(shù)的定義［1］設(shè)計(jì)的數(shù)字式BJ參數(shù)測試系統(tǒng)原理框圖如圖1所示。該系統(tǒng)主要包括測試模塊（圖1中虛線框中的部分）和控制模塊。測試模塊主要完成集電極電流以及vBE和vCE等的取樣及信號(hào)調(diào)理；控制模塊主要實(shí)現(xiàn)數(shù)控電流源、數(shù)控電壓源的控制以及數(shù)據(jù)的采集、LCD液晶顯示器的控制等。測量放大倍數(shù)時(shí)，微控制器通過控制數(shù)控電流源為三極管基極提供合適的基極電流iB；通過數(shù)控電壓源為三極管的集電極提供適當(dāng)?shù)募姌O電壓vC。現(xiàn)假設(shè)通過的集電極電流為iC，iC經(jīng)集電極取樣電阻取樣后進(jìn)行差動(dòng)放大，這樣就可以得到與iC成正比的電壓信號(hào)kiC（k為放大系數(shù)），再將該信號(hào)送入A/D轉(zhuǎn)換器進(jìn)行模/數(shù)轉(zhuǎn)換，微控制器讀入采樣的電壓值，并根據(jù)數(shù)控電流源提供的基極電流iB通過BJ直流放大倍數(shù)的定義式(1)即可算出直流放大倍數(shù)。