Transcription of MT-037: Op Amp Input Offset Voltage - Analog Devices
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MT-037: Op Amp Input Offset Voltage - Analog Devices
MT-037 TUTORIAL Op Amp Input Offset Voltage DEFINITION OF Input Offset Voltage Ideally, if both inputs of an op amp are at exactly the same Voltage , then the output should be at zero volts. In practice, a small differential Voltage must be applied to the inputs to force the output to zero. This is known as the Input Offset Voltage , VOS. Input Offset Voltage is modeled as a Voltage source, VOS, in series with the inverting Input terminal of the op amp as shown in Figure 1. , 10/08, WK Page 1 of 10 zzzzzzzOffset Voltage : The differential Voltage which must be applied to the Input of an op amp to produce zero :Chopper Stabilized Op Amps:<1 VGeneral Purpose Precision Op Amps:50-500 VBest Bipolar Op Amps:10-25 VBest JFET Input Op Amps:100-1,000 VHigh Speed Op Amps:100-2,000 VUntrimmed CMOS Op Amps:5,000-50,000 VDigiTrim CMOS Op Amps:<100 V-1,000 V-+VOS Figure 1: Typical Op Amp Input Offset Voltage Chopper stabilized (also called auto-zero) op amps have a VOS which is less than 1 V ( AD8538, AD8551, AD8571, AD8628, AD8630), and the best precision bipolar op amps (super-beta or bias stabilized) can have maximum offsets as low as 25 V (OP177F).
Input offset voltage varies with temperature, and its temperature coefficient is known as TCVOS, or more commonly, drift. Offset drift is affected by offset adjustments to the op amp, but when the offset voltage of a bipolar input op amp has been minimized, the drift may be as low as 0.1 µV/°C (typical value for
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