6.5.1 Simulation Using MINIMOS-NT

The output voltage of the oscillator simulated by MINIMOS-NT is plotted in Fig. 6.16. After approximately 80 ns the output voltage reaches its steady state value with a maximum of 7.6 V.

**Figure 6.16:** Oscillator output voltage simulated by *MINIMOS-NT*.
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Fig. 6.17 shows a plot of the oscillation frequency as function of the simulation time. During the first periods the frequency reduces from a maximum of 181 MHz to the steady state oscillation frequency of 109.8 MHz which is reached after approximately 40 ns. The change of the oscillation frequency is caused by the variation of the junction capacities which depend on the voltages applied to the junctions. During the first periods of the oscillation the amplitude is very small and gradually builds up to its steady state value. This changes the junction capacities and thereby the oscillation frequency.

**Figure 6.17:** Oscillation frequency simulated by *MINIMOS-NT*.
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Fig. 6.18 shows the base-emitter voltage which oscillates between 0.53 V and 0.98 V. This strong variation of the bias point causes strong variations of the current gain and of the base-emitter junction capacity.

**Figure 6.18:** Base-emitter voltage simulated by *MINIMOS-NT*.
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In the steady state the collector-emitter voltage oscillates between 0 V and 6.9 V. Resonance of the LC circuit which is used for feedback of the output signal and for tuning the oscillation frequency leads to output voltages which are more than double as high as the supply voltage (see Fig. 6.19).

**Figure 6.19:** Collector-emitter voltage simulated by *MINIMOS-NT*.
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The transient simulation was performed on a workstation equipped with a 266 MHz Pentium II processor and took approximately 3000 s of CPU time. The number of unknowns for this simulation was 3300.