The asymptotic gain model (also known as the Rosenstark method) is a representation of the gain of negative feedback amplifiers given by the asymptotic gain relation:

${\displaystyle G=G_{\infty }\left({\frac {T}{T+1}}\right)+G_{0}\left({\frac {1}{T+1}}\right)\ ,}$

where ${\displaystyle T}$ is the return ratio with the input source disabled (equal to the negative of the loop gain in the case of a single-loop system composed of unilateral blocks), G_∞ is the asymptotic gain and G₀ is the direct transmission term. This form for the gain can provide intuitive insight into the circuit and often is easier to derive than a direct attack on the gain.

Figure 1 shows a block diagram that leads to the asymptotic gain expression. The asymptotic gain relation also can be expressed as a signal flow graph. See Figure 2. The asymptotic gain model is a special case of the extra element theorem.

As follows directly from limiting cases of the gain expression, the asymptotic gain G_∞ is simply the gain of the system when the return ratio approaches infinity:

${\displaystyle G_{\infty }=G\ {\Big |}_{T\rightarrow \infty }\ ,}$

while the direct transmission term G₀ is the gain of the system when the return ratio is zero:

${\displaystyle G_{0}=G\ {\Big |}_{T\rightarrow 0}\ .}$