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Next: 7.2.5 The Current Gain Up: 7.2 The Bias Dependence Previous: 7.2.3 The Gate Drain

7.2.4 Further Small-Signal Elements

The output conductance $ {\it g}_{\mathrm{ds}}$ is given in Fig. 7.13. The extracted RF- $ {\it g}_{\mathrm{ds}}$ is always positive. The qualitative and the quantitative behavior of $ {\it g}_{\mathrm{ds}}$ are modeled correctly. A typical value of $ {\it g}_{\mathrm{ds}}$= 50 mS/mm is observed for a class A bias, i.e. $ {\it I}_{\mathrm{D}}$ = 50% $ {\it I}_{\mathrm{Dmax}}$, for this pseudomorphic device. The dependence of the phase term $ {\it\tau }$ to $ {\mit g}_{\mathrm{m}}$ is found in Fig. 7.14 in comparison with measurements. Both the qualitative and the quantitative are reproduced by the simulations correctly. $ \tau$ rises as a function of $ {\it V}_{\mathrm{GS}}$ for $ {\it V}_{\mathrm{DS}}$= 2.0 V. A maximum can be observed for the maximum $ {\mit g}_{\mathrm{m}}$. For higher $ {\it V}_{\mathrm{GS}}$ $ \tau$ slightly drops. When the diode opens for $ {\it V}_{\mathrm{GS}}$$ \approx $ 0.7 V $ \tau$ sharply rises in the simulation in agreement with the measurements shown.

Figure 7.13: Simulated and measured RF-$ g_{ds}$ as a function of bias $ V_{GS}$ for $ V_{DS}$= 2 V.

\includegraphics[width=10 cm]{D:/Userquay/Promotion/HtmlDiss/fig43d.eps}
Figure 7.14: $ \tau$ as a function of $ V_{GS}$ bias for $ V_{DS}$= 2 V.
\includegraphics[width=10 cm]{D:/Userquay/Promotion/HtmlDiss/fig43e.eps}

Fig. 7.15 shows the bias dependence of $ {\it C}_{\mathrm{ds}}$ as a function of $ {\it V}_{\mathrm{GS}}$ for $ {\it V}_{\mathrm{DS}}$= 2 V. A nearly constant behavior is also observed in the simulation which underestimates the available data.

Figure 7.15: The drain-source capacitance $ C_{ds}$ as a function of $ V_{GS}$ bias for $ V_{DS}$= 2 V.


\includegraphics[width=10 cm]{D:/Userquay/Promotion/HtmlDiss/fig42a.eps}

next up previous
Next: 7.2.5 The Current Gain Up: 7.2 The Bias Dependence Previous: 7.2.3 The Gate Drain
Quay
2001-12-21