JUNCTION TEMPERATURE-MEASUREMENTS IN REVERSE-BIASED PIN DIODES

Designers using reverse-biased PIN diodes at high power levels (to thousands of watts) have always faced a complex problem in choosing the optimal reverse bias voltage. Because the conservative approach of using bias voltage equal to the peak applied rf voltage can lead to excessive cost and complexity, operation with reduced or weak bias where the diode makes excursions into the forward bias direction is attractive if heat dissipation can be controlled. A method is presented here for measuring temperature rise in the PIN diode under weak reverse bias. The measurement of junction temperature under actual operating conditions provides an important tool both for choosing the appropriate bias voltage and for evaluating the reliability of the design. For diodes operating in the capacitive (nonconductive) regime, it is further shown that temperature rise at high bias voltages and high rf power levels can be predicted accurately from low power data.