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TINA/Spice/LM7171: High value resistors causing DC shift in output

eshwar j
Prodigy 110 points
Part Number: LM7171
Other Parts Discussed in Thread: TINA-TI,

Tool/software: TINA-TI or Spice Models

Hi, i have simulated LM7171 for low and high resistor values for the same gain. For low resistance values, the simulation results are fine. However i have observed a DC shift of about 1.5V at output when i use high resistance values for same gain compared to low resistance values. It is a design requirement so i have to use high resistors in my design even for smaller gains. I have excited the circuit with 2Vpp at 2Meg in both cases. Please suggest way to remove DC offset.

  • 0
    Guru 140200 points

    Hi Eshwar,

    you have forgotten that the LM7171 has an input bias current of about 3µA. 3µA x 500k = 1.5V. :-)

    The LM7171 is a HF OPAmp and should be used in combination with small feedback resistors, especially to make the circuit immune to the impact of stray capacitance. See also figure 54 of datasheet.

    Kai