Typical small-signal parameter measurements are shown in Figure 5 and performance data for various models is presented in Table 1.
In the development process, simulations were used, together with microwave measurements, to optimize small-signal parameters and third-order intermodulation products.
Using small-signal parameters
, the start-up condition can be checked, and with the transistor's large-signal S-parameters at a certain input or output power, the oscillator can be designed the way that the true loop power will meet the large-signal estimate.
The small-signal parameters
of the transistor equivalent circuit are listed in Table 1.
In this article, small-signal parameters
are defined, a simple unstable RLC circuit for which the criterion of Equations 1 and 2 fails is analyzed, conditions under which it can be applied are presented and the Nyquist stability criterion is discussed.
A DC large-signal model defines the set of nonlinear equations describing the behavior of the drain-source current, transconductance and output conductance, which LASIMO optimizes to match the corresponding measured, bias-dependent small-signal parameters
. Similarly, a capacitance large-signal model defines the nonlinear equations describing the behavior of the gate-source capacitance and gate-drain capacitance, which the program optimizes to match the corresponding measured, bias-dependent small-signal parameters
An automatic data-acquisition program with the capability to extract the heterostructure FET (HFET) small-signal parameters
directly is presented.
Since small-signal parameters
are derivatives of a nonlinear function, accuracy cannot be ensured by this method by deriving the small-signal parameters