# An Adaptive 24 GHz PSO-Based Optimized VCO in Next-Generation Wireless Sensor Networks
## 4 Result and Discussion  
Figures 12 and 13 show the comparison of the simulated phase noise of the designed VCO using GA and SA and by using the adaptive PSO algorithm and without the adaptive PSO algorithm, respectively. In Figure 12, at 1 MHz frequency offset, we can see the VCO phase noise performance using GA and SA. The phase noise of the VCO using GA is \(-118.5\) dBc/Hz. Meanwhile, for SA, it is \(-116.9\) dBc/Hz. In Figure 13, at 1 MHz frequency offset, we can see that the adaptive PSO outperformed the VCO without the adaptive PSO algorithm with almost \(-4.7\) dbc/Hz enhancement in the phase noise value. The phase noise of the VCO with the adaptive PSO algorithm is \(-120\) dBc/Hz @ 1 MHz and \(-140\) dBc/Hz @ 10 MHz. The phase noise of VCO without an algorithm is \(-115.3\) dBc/Hz @ 1 MHz and \(135.3\) dBc/Hz @ 10 MHz.  
Figure 14: VCO phase noise performance versus tuning voltage.  
Figure 12: VCO phase noise performance using GA and SA.  
Figure 13: VCO phase noise performance with and without an adaptive PSO.  
The optimized VCO oscillating frequency range with respect to the tuning voltage of varactors, which ranges from 0 V to 1 V, is illustrated in Figure 15. The optimized VCO with an adaptive PSO oscillates with a frequency range of 21.2%, and the center oscillation frequency of the optimized VCO is 24.2 GHz. The wide frequency range of an optimized VCO is achieved with the aid of C2 varactors that form a parallel connection with the source terminal of transistors \(MP_{CR}\) and \(MN_{CR}\).  
The transient response of the optimized VCO provides symmetrical and differential waveforms, such as Vout+ and Vout-, which are depicted in Figure 16.  
The designed VCO is simulated under different processes, environments, and state conditions to verify the VCO operation under different PVT conditions. The Monte Carlo simulation with three different semiconductor process corners, defined as follows, is used to verify the stable operability of VCO:  
Best case: (FF) corner process (0.45 V, \(-\)55 \({}^{\circ}\)C);  
Typical case: TT corner process (0.4 V, 27 \({}^{\circ}\)C);  
Worst case: SS corner process (0.35 V, 125 \({}^{\circ}\)C).  
Figure 16: Output signal waveforms of the designed VCO.  
Figure 15: Frequency range of the optimized VCO.  
The variations of phase noise of the designed VCO with respect to PVT are simulated using the Monte Carlo simulation. Histograms of the phase noise are shown in Figure 17 below. The mean value of phase noise is -120.06 dBc/Hz, and its standard deviation is 1.47%.  
The simulation results with respect to PVT variation at semiconductor process corners are shown in Table 4. The VCO oscillates in all three studied corners. In the FF corner, power consumption and frequency drift by 11.5% and 0.1%, respectively, compared to the TT corner. In the SS corner, power consumption and frequency drift by 12.6% and 0.41%, respectively, compared to the TT corner.  
The performance parameter comparison of the adaptive PSO-based optimized VCO with [23; 24; 25; 26; 27; 28] state-of-the-art published work is provided in Table 5. Table 5 depicts the better performance of the designed VCO over other published works from the perspective of performance parameters like phase noise, which is \(-120\) dBc/Hz @ 1 MHz offset, and oscillating frequency range, which is 21.2%.