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Historically, the biggest single problem with the application ofop amps has been the input offset voltage. This is indicatedby the fact that almost all important op amps from the μA741and LM101 on have offered offset null adjustment pins, specialscreening to low offset voltage values, and/or internalVOS trimming (laser or Zener-zap). Also consider the extensiveseries of specifications devoted to its variability withtemperature, time, common-mode voltage (CMRR), powersupply (PSRR), output voltage (AVOL), and sometimes evendown to variation of temperature drift with offset null correction.Contrast this with the treatment afforded one otherimportant (error-causing) input parameter, input bias current,which usually gets lust a specified value under one set ofconditions, a variation over temperature, and a term relatingto its matching between the two inputs. If variation with common-mode voltage, power supply voltage, etc., is covered, itis generally only in a “typical curve” buried in the middle ofthe data sheet.
