Asymptotic Gain Model - Implementation

Implementation

Direct application of the model involves these steps:

1. Select a dependent source in the circuit.
2. Find the return ratio for that source.
3. Find the gain G_∞ directly from the circuit by replacing the circuit with one corresponding to T = ∞.
4. Find the gain G₀ directly from the circuit by replacing the circuit with one corresponding to T = 0.
5. Substitute the values for T, G_∞ and G₀ into the asymptotic gain formula.

These steps can be implemented directly in SPICE using the small-signal circuit of hand analysis. In this approach the dependent sources of the devices are readily accessed. In contrast, for experimental measurements using real devices or SPICE simulations using numerically generated device models with inaccessible dependent sources, evaluating the return ratio requires special methods.