集成电路运算放大器的节拍场效应管输入电流-IC Op Amp Beats FETs on Input CurrentA monolithic operational amplifier having input error currentsin the order of 100 pA over a −55°C to 125°C temperaturerange is described. Instead of FETs, the circuit used bipolartransistors with current gains of 5000 so that offset voltageand drift are not degraded. A power consumption of 1 mW atlow voltage is also featured.A number of novel circuits that make use of the low currentcharacteristics of the amplifier are given. Further, special designtechniques required to take advantage of these low currentsare explored. Component selection and the treatmentof printed circuit boards is also covered.INTRODUCTIONA year ago, one of the loudest complaints heard about IC opamps was that their input currents were too high. This is nolonger the case. Today ICs can provide the ultimate in performancefor many applications—even surpassing FET amplifiers.FET input stages have long been considered the best way toget low input currents in an op amp. Low-picoamp input currentscan in fact be obtained at room temperature. However,this current, which is the leakage current of the gate junction,doubles every 10°C, so performance is severely degraded athigh temperatures. Another disadvantage is that it is difficultto match FETs closely.1 Unless expensive selection and trimmingtechniques are used, typical offset voltages of 50 mVand drifts of 50 μV/°C must be tolerated.