SBOA550 October   2022 OPA1671 , OPA2990 , SN74HCS04 , SN74HCS164 , SN74HCS30 , SN74LVC1G00 , SN74LVC1G123 , TLC04 , TLC14 , TS5A9411

 

  1.   Abstract
  2.   Trademarks
  3. 1 Introduction
  4. 2 The Davies Generator
  5. 3 Optimizing Standard Resistance Values for THD Performance
  6. 4 Simulation Examples
  7. 5 Compensating for Shift Register Output Resistance
  8. 6 Voltage-Mode Thevenin Equivalent
  9. 7 Harmonic Filtering
  10. 8 Tracking Harmonic Filter
  11. 9 Multiphase Output
  12. 10Conclusion
  13. 11Acknowledgment
  14. 12References
  15.   A Analytical Solution for Resistance Network Values
  16.   B Forbidden States of the Johnson Counter

6 Voltage-Mode Thevenin Equivalent

The examples shown so far have operated in a current-mode fashion, that is, driving current into a virtual ground. Due to the numerous parallel resistors involved, this mode of operation is easier to analyze (per Appendix A) than the voltage mode equivalent. Often it is useful to operate in voltage mode and a simple Thevenin transformation results in a voltage source having peak-to-peak amplitude of VCC – VEE and an output resistance of the parallel combination of all the resistors, which is chosen as a design parameter. Figure 6-1 shows a voltage mode version and the open-circuit voltage response; notice the common mode DC offset of
2.5 V in the output.

Figure 6-1 Voltage Mode Operation and Open-Circuit Output Transient Response, RThev. ≈ 597.6 Ω

The Thevenin output resistance can be used as an element of a harmonic filter to further improve distortion performance as demonstrated in Section 7.