SLAA946 April   2021 AFE10004

 

  1.   Trademarks
  2. 1LDMOS and GaN Power Amplifier FET Basics
  3. 2VGS Compensation
  4. 3Sequencing
  5. 4An Integrated PA Biasing Solution
  6. 5Temperature Compensation
  7. 6Fast Output Switching
  8. 7Controlled Sequencing With the AFE10004
  9. 8Conclusion

2 VGS Compensation

The IDS also depends on the temperature of the FET. The IDS variations due to thermal drift create the need to compensate by adjusting one of the other two variables in the system: VD or VGS. It is easier to adjust VGS, as only small voltage changes are required. Conversely, VD needs to change significantly if the device is operating in the flat areas of Figure 1-2, making it infeasible to compensate for the thermal drift by adjusting VD.

GUID-B9873847-A5D6-4882-AF54-7E951480E4B8-low.gifFigure 2-1 FET VGS Bias Voltages

Figure 2-1 shows VGS needs to be adjusted to ensure a static IDS. Applications utilizing these FETs require this kind of compensation to ensure that the power of the antenna system is tightly controlled. VGS compensation can be implemented by either measuring the temperature of the FET, or measuring the IDS using a current shunt and adjusting the VGS accordingly.