SBOA583 December   2023 OPA205 , OPA206 , OPA210 , OPA2206 , OPA2210 , OPA2392 , OPA2828 , OPA320 , OPA328 , OPA365 , OPA392 , OPA397 , OPA828

 

  1.   1
  2.   Abstract
  3. 1 Introduction
  4. 2 Circuit Configuration Impact on Common-Mode Range
  5. 3 Practical Input Limitations
  6. 4 Input Phase Reversal (Inversion)
  7. 5 Common-Mode Limitations Inside Bipolar Amplifiers
  8. 6 Common-Mode Limitations Inside CMOS Amplifiers
  9. 7 Rail-to-Rail CMOS Amplifiers
  10. 8 Output Swing Limitations Inside a Bipolar Op Amp
  11. 9 Linearity of Output Swing Specifications
  12. 10Output Voltage Swing vs Output Current
  13. 11Classic Bipolar vs Rail-to-Rail Output Stage for CMOS and Bipolar
  14. 12Rail-to-Rail Output and Open-Loop Gain Dependence
  15. 13Output Short-Circuit Protection
  16. 14Overload Recovery
  17. 15Supply Current During Input and Output Swing Limitations
  18. 16Summary
  19. 17References

8 Output Swing Limitations Inside a Bipolar Op Amp

At room temperature, the classic bipolar output stage shown in Figure 8-1 has an output swing limitation of approximately 0.9 V from the supply rail. In this example, for linear operation the minimum voltage from the output to the positive supply can be calculated as the sum of the base-to-emitter voltage of Q1 and the saturation voltage of Q3 (Vbe + Vsat = 0.7 V + 0.2 V = 0.9 V). Other more complex topologies can have even greater output swing limitations. It is not unusual for bipolar devices to have between 1-V and 2-V output swing limitations depending on the design. Later sections cover how both CMOS and bipolar rail-to-rail output configurations can swing much closer to the supply rails.

GUID-20230928-SS0I-PQMF-QPWD-JFJNQHPN9CZH-low.svg Figure 8-1 Bipolar Output Stage Example Where Swing is Limited to 0.9 V From Supply