##### From Wideband Amplifier Design

## 2.8 AN EXAMPLE

For an example, I will use a real-world transistor NEC part number NE851M03. It is an RF NPN small-signal device with an *f _{t}* approximately equal to 8 GHz at

*I*= 20 mA, and

_{C}*V*= 3 V. For purposes of this book, it has the advantage of being fairly well characterized with SPICE parameters, packaging parameters and "s-parameters" provided by the manufacturer. The actual parameters are given in Appendix A. With these data, one can now begin to compare the accuracy of the high-frequency models against the actual SPICE model.

_{CE}Assume that we are using the NE851M03 in the emitter-follower circuit shown in Figure 2-22 with a 4 pF load. The operating point is *V _{CE}* = 3 V,

*I*= 20 mA, making

_{C}*g*= 0.7737 S. There is a 10 nH inductor in the base. The NE851M03 has

_{m}*f*= 7.95 GHz at this operating point.

_{t}This gives *T _{t}* = = 20.03 ps and

*C*=

_{?}*g*= 15.5 pF.

_{m}T_{t}From the SPICE parameters table, we see that the transistor has an emitter resistance *R _{eb}* = 1.7 ?. (The actual SPICE parameter is labeled

*R*.) This gives

_{E}Because *C _{eb}* is in series with

*C*, the combination is

_{?}*C*

_{bt}: *R _{bb}*, as listed in the SPICE table, is 1 ?

*. R*

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