Scaling of microwave noise and small-signal parameters of InP/InGaAs DHBT with high DC current gain

The scaling of noise and small-signal parameters of InP double heterojunction bipolar transistors (DHBTs) with high dc gain are presented for the first time in this brief. As InP DHBTs have very low surface recombination and high dc current gain, the large size device can be viewed as consisting of n identical subcells. Using this approach, a set of equations was derived, which relate the noise and small-signal parameters between the large-size device and the subcells for scaling purposes. The experimental and theoretical results show that at the same collector current density and collector-emitter voltage, good scaling of the noise and small-signal parameters can be achieved between the large-size device and the subcells. Because of the nonscalable external base-collector capacitor (C_bc), the effects of C_bc on the noise and small-signal parameters are also investigated. The large base-collector capacitance acts as a negative feedback providing the lower minimum noise figure value and higher value of the imaginary part of the optimum source admittance. The good agreement between the measured and the calculated results supports the scaling approach developed in this work for InP DHBTs that may be useful for the design of high frequency circuits using InP-based HBTs.