Bootstrapped Input For High Impedance

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Bootstrapping involves the use of a small amount of positive feedback from output to input of an amplifier, of nearly unity gain. The bootstrap technique is used to make a low value input resistor, R3 in this case, appear to have a much higher value as seen by the input signal. Without feedback the input resistance is R3 (1M) in parallel with the input resistance of U1 (1E13 ohms).Positive feedback applied through the voltage divider R1- R2 multiplies the effective input impedance of R3.Adding bootstrapping also increases the noise gain of the op amp, multiplying its Vos, drift, and noise. Adding a LARGE capacitor in series with R1 can eliminate the amplified DC offset and drift but the low frequency noise will still suffer.

  • Free
  • Simple
  • 11-20
  • TINA
  • 7+
  • No
  • output voltage AC response for R1 100 Ohm AC analysis for different R1 values


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