[ 50W Transmission Line at the Base ] The base is extended by a length of 50W transmission line to move (or rotate) the fM to the real-axis on the -Y-Smith-Chart. From Serenade®, it will be 71° (183 mils) long (at 8.2GHz). The idea is figuratively described in Fig. 6.
The purpose of this piece of transmission line to rotate the GOUT curve to the left hand side of the -Y-Smith-Chart. Let's rename GOUT to GJ. Since our GJ is greater than one, the real part of ZJ is less than zero (also the real part of YJ,) we call this the negative resistance (or negative conductance.) Fig.6 shows these negative admittance (-YOUT and -YJ) Smith Charts. Fig.7 shows the simulation result. One may ask why we need this piece of transmission line. The answer is, since YJ (or ZJ) at this point is purely real, it will be easier for us to design each branch of the Coarse Tune, Fine Tune, and RF Output.
Fig.7 -YJ at the Junction
[ RF Output ] In order to loosely couple the system, the RF Output configuration is designed to be a 10mil wide l/4 transmission line connected to a 100mil wide l/4 transmission line. (Fig.8) This configuration is used to increase the system stability and reduce phase noise. If too much power is coupled from the system to the output, the circuit is no longer an isolated system.
[ Details of Load Network Parameters ] In order to have a more detailed discussion, we modify Fig.1 to include some more parameters (Fig.14)
Recall the oscillation condition. In order to make the Coarse Tune Design easier, we include RF Output to the left hand side, and leave only the Coarse Tune at the right hand side (Fig.16) Then the -YLHS Smith Chart is plotted in Fig.17
Fig.17 -YLHS Smith Chart
[ Coarse Tune Design ] Please go to the next page
| Introduction | Measurements | Fundamental Theory | Transistor Selection |
| Terminating Network Design | Load Network Design | Coarse Tune Design |
| DC Bias Circuit Design | Fine Tune Design | Phase Noise |