Very low frequency s-parameter measurements for transistor noise modeling

Correct measurement of low frequency noise in a transistor requires prior knowledge of its s-parameters but the measurement of s-parameters at very low frequencies are difficult due to long time constants of the measurement setup and instabilities in the transistors. We report a method to stabilize and measure the s-parameters of GaAs heterojunction bipolar transistors (HBT) at frequencies as low as 10 Hz to 1 MHz, and discuss an industry standard transistor model at these frequencies.