Analysis of intermodulation distortion in GaAs/AlGaAs HBT´s

An attempt has been made to explain the third-order intermodulation distortion properties of the heterojunction bipolar transistor (HBT) at millimeter wave frequencies. The frequency and bias dependence of the third-order intercept point is presented for a typical HBT. A conventional tuner system was used for measurements from 8 to 16 GHz. Beyond 27 GHz, an active load pull system was used to circumvent insertion loss problems. Appropriate corrections to the active load pull intercept measurements are described. To aid in understanding the measured results, a simple model which includes transit time effects was developed. From the measured and modeled results, it was found that reductions in V/sub ce/ resulted in a reduction in third-order intercept point. This degradation was attributed to increased nonlinearity in base collector capacitance.<>