Time-Domain Spectrometry of High Frequency Transistors Measured under Transient Bias Conditions

Time-Domain Spectrometry has been used to measure S-parameters of high frequency power transistors, bipolar and MOS, under pulsed bias conditions to reduce the mean dissipation and hence the rise in temperature of the active device. For the bipolar transistors, |S2l| shows a much slower decrease at high currents than conventional measurements made under steady bias. In the case of the MOS device, |S2l| approaches a constant value at high currents showing that the fall in magnitude normally observed is due entirely to the increase in device temperature. It is suggested that this method can be applied to measurements under other transient conditions provided that the system response does not change within the sampling window of 10 ns.