Other Parts Discussed in Thread: TL082
How is the value of R3 calculated when R2 =600k，R1=100k ?
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For an op amp with significant input bias current, R3 = R1 || R2 = (R1 * R2) / (R1 + R2)
TL082 does not have significant input bias current so R3 could be zero. However make R3 between 1k and 10k to protect input pin from system faults or poor layouts.
take care, your feedback resistors are such high ohmic that you will run into stability issues. Your phase margin is smaller than 4°:
Better add a phase lead capacitance of 4.7p...10p, as shown below:
C1 restores the phase margin to 74° and ensures stability