2 V_GS Compensation

I_DS is dependent on the temperature of the PA. The I_DS variations due to thermal drift create the need to compensate the PA by adjusting one of the other two variables in the system: V_DRAIN or V_GS. Although there are many reasons why adjusting V_DRAIN is implemented in different RF applications, the response of the output power is minimal compared to the change in the V_DRAIN voltage, as shown in Figure 1-2. Adjusting V_GS allows for faster response time and total amplitude of the output power making it more practical for temperature compensation and other applications.

Figure 2-1 GaN PA V_GS Bias Voltage vs Temperature to maintain constant I_DS

Figure 2-1 shows V_GS needs to be adjusted to ensure a static I_DS due to thermal drift. Applications utilizing these PAs require implementing this kind of compensation to ensure that the power of the antenna system is tightly controlled. V_GS compensation can be implemented by either measuring the temperature of the PA, or measuring the I_DS using a current shunt and adjusting the V_GS accordingly.