SBOA503 July   2021 INA101 , INA103 , INA111 , INA114 , INA115 , INA118 , INA121 , INA122 , INA125 , INA126 , INA128 , INA128-HT , INA129 , INA129-EP , INA129-HT , INA141 , INA155 , INA156 , INA1620 , INA163 , INA1650 , INA166 , INA188 , INA2126 , INA2128 , INA2141 , INA217 , INA2321 , INA2331 , INA2332 , INA317 , INA321 , INA322 , INA326 , INA327 , INA330 , INA331 , INA332 , INA333 , INA333-HT , INA333-Q1 , INA337 , INA338 , INA818 , INA819 , INA821 , INA823 , INA826 , INA826S , INA827 , INA828 , INA848 , INA849

 

  1.   Trademarks
  2. 1Typical Instrumentation Amplifier Operation
  3. 2Problem Statement
  4. 3Common Mistake
  5. 4Proposed Solution
  6. 5Component Selection and Trade-Offs
  7. 6Common Applications
  8. 7Conclusion

3 Common Mistake

Eliminating the dc nonlinearity at the output due to the presence of a dc input voltage is important. Engineers often mistakenly configure an ac-coupled IA circuit by adding a capacitor in series with each input terminal, but without providing a path for the input bias current. This mistake is illustrated in Figure 3-1. If a capacitor is connected in series with an instrumentation amplifier input without a dc path for current to flow, then over time, the Ib of the IA charges the capacitor until the output is driven to one of the rails, as shown by the IN+ trace in Figure 3-1.

Figure 3-1 Incorrect AC-Coupling Schematic and Transient Analysis