X-Parameters: The µ Stability Factor and its Application to Avoid Oscillation Problems During the Characterization of Power GaN FETs

This work investigates the influence of the input power on the stability of power GaN FETs by using the µ stability factor computed with X-parameters. The results of the proposed stability analysis corroborate the direct relation between the stability and the transistor gain and identify two operation bands in which the GaN FET tends to be more unstable at the low band. In the lower band, the transistor becomes more stable as the input power increases, whereas, in the high band, the stability behavior is the opposite. Furthermore, a technique to select the values of the frequency-dependent R-C stabilization network in the gate of the transistor is discussed. S-parameters measured data of an unstable power GaN FET CGH40006P was stabilized using our solution, obtaining data free of instabilities.