# Design and Implementation of 24-GHz and 48-GHz VCOs Using Noise Filtering Technique in 90-nm CMOS
## 3 Implementation and Experimental Results  
Both the two VCOs that the 24-GHz design adds a noise filter to reduce phase noise and the 48-GHz design that uses the push-push architecture are fabricated using the TSMC 90-nm CMOS process. The process provides a single poly layer and nine metal layers (1P9M) for interconnections. The chip size, including RF and DC testing pads of 24-GHz VCO, is 0.68 mm \(\times\) 0.69 mm, and the push-push VCO is 0.7 mm \(\times\) 0.7 mm, respectively.  
On-wafer measurements were performed to characterize the output spectrum, tuning range and phase noise. For the 24-GHz VCO measurements, two ground-signal-ground (GSG) RF probes were used for differential output at the power supply end, one PGPPGP DC probe for VDD, Vctrl and for the two output buffer gate terminals' DC supply, and one PGP probe DC probe for the current mirror bias VB. There are bypass capacitors on the DC lines to reduce low-frequency noise, as shown in Figure 8a. As for the 48-GH z push-push VCO, one GSGSG RF probe was used for the 48-GHz output signal, one PGP DC probe for VDD and Vctrl, one PGP DC probe for output buffer gate terminals, and the current mirror bias VB, as shown in Figure 8b.  
Figure 7: Schematic of the proposed 48 GHz Push-Push VCO.  
Figure 9 shows the measured output spectrum of the proposed VCO; the measurement DC current of VCO without buffer is 5.1 mA, 6.12 mW. When V\({}_{\text{ctrl}}\) is 0.6 V, the output frequency of the voltage-controlled oscillator is 24.37 GHz and the output power is \(-\)0.65 dBm. Figure 10 shows the measured tuning range of the proposed 24 GHz VCO. When the control voltage V\({}_{\text{ctrl}}\) varies from 0 to 1.2 V and the frequency range is 23.51\(\sim\)25.09 GHz, the tuning range is 6.5%. When measuring the tuning range, we set the control voltage sweep points to 201 points. This will cause the VCO output frequency to change discontinuously when the sweep range is wide. If a higher number of points (such as 801 points) is used for scanning, the curve will become smoother and more continuous. Figure 11 shows the measured phase noise of the proposed 24 GHz VCO; the phase noise measured at a 1 MHz offset is \(-\)97.2 dBc/Hz, and that measured at a 10 MHz offset is \(-\)121.9 dBc/Hz.  
Figure 12 shows the measured output spectrum of the proposed push-push VCO. The measurement DC current of the design without buffers is 5.74 mA, and \(P_{\text{out}}\) is 6.89 mW. In Figure 12a, when V\({}_{\text{ctrl}}\) is 0.6 V, the output frequency of the \(f_{0}\) is 24.92 GHz and the output power is \(-\)2.15 dBm. In Figure 12b, when V\({}_{\text{ctrl}}\) is 0.6 V, the output frequency of the \(2f_{0}\) is 49.76 GHz and the output power is \(-\)25.29 dBm. Figure 13 shows that the measured tuning range of the push-push VCO. With the control voltage \(V_{\text{ctrl}}\) varying from 0 to 1.2 V, the frequency range of \(f_{0}\) is 24.1-25.9 GHz and that of \(2f_{0}\) is 47.1-51 GHz. Figure 14 shows the measured phase noise of the VCO. In Figure 14a,b, the measured phase noises of \(f_{0}\)  
Figure 8: Chip photo of the proposed (**a**) 24-GHz and (**b**) 48-GHz push–push VCOs.  
Figure 9: Measured output spectrum of the proposed 24 GHz VCO.