Chapter 4 Design of Low-Power Current-Reused with Balance Resistors
4.3 Current-Reused VCO with Balance Resistors VCO Simulation and Measurement
4.3.3 WiMAX WSC System VCO Measurement Characteristics
In this section, we will discuss measurement results. The measurement results demonstrate the central oscillation signal of 2.29 GHz to be associated with the 180 MHz turning range, 2.2 to 2.39 GHz and -120 dBc/Hz phase noise at 1 MHz offset. The power consumption of the VCO core is only 3.96 mW. The measurement result evaluated by means of a figure of merit factor is -180.87 dBc/Hz by equation (3.2).
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Figure 4.13 Measurement Phase-noise result of WiMAX WSC current-reused VCO
Figure 4.14 Measurement current result of WiMAX WSC current-reused VCO
Figure 4.15 Measurement turning range result of WiMAX WSC current-reused VCO
Figure 4.16 Measurement spectrum result of WiMAX WSC current-reused VCO
Figure 4.17 Microphotograph of wire bounding VCO
Figure 4.18 CPW transmission line structure layout
Figure 4.19Measurement result of WiMAX WSC current-reused VCO waveform
Using CPW transmission line structure layout is shown in Figure 4.18, Figure 4.17 wire bounding on FR4 PCB and Figure 4.18 is measurement result for waveform by Agilent 54855A Oscilloscope which very well phase only 0.7 degree inaccurately.
Table 4.7 Simulation and measurement of WiMAX WSC Results
Simulation Measurement
Frequency 2.661GHz ~2.37GHz 2.39~2.2GHz
Output-power P
out.(dBm) -5 dBm -3.4dBm~-4.2dBm
Power consumption (total) 0.432mW, 1.85mW
(core, with buffer) 3.96~4.668mW
Turning Range 11.57% 7.86%
Phase-Noise@100KHz -99 -91~-83
Phase-Noise@1MHz -120 -117~-120
FOM (power with buffer) -184.82(1.836mW)@1M -180.87(3.96mW)@1M
Die Size 1.24 X 1.11 mm
4.4 Discussion and Summary
We introduced a Current-Reused Configuration with balance resistors Included Output-Buffer VCO Circuit techniques. In above sections, we knew that VCO has very simple structure and good performance in measurement results. But that has some performance limitation that maybe can fix by other techniques like relate of ISF fix techniques, custom inductance (High Q factor) and new VCO structures overcome
A 1.2V Low-Power CMOS Voltage-controlled oscillator (VCO) had built by current-reused configuration with Output-Buffer and two drain resistors used in order to improve magnitude symmetry of output signals for IEEE 802.16e, by TSMC 0.18μm mixed signal/RF process. A Good performance was measured with this design. The VCO circuit resonator was applied between 2.21~2.39 GHz under the turning voltage between 0 to 1.2 V , Output power -4.2dBm and phase-noise -120dBc/Hz at 1-MHz offset frequency. The power consumption of the VCO only 3.96mW at 1.2V voltage supply with buffer included.
Chapter 5
Conclusions and Future works
5.1 Conclusions
Three chips of low power integrated CMOS VCO has been designed using in L-band, WiMAX application respectively. Those VCO are based on a low power-consumption architecture using a TSMC 0.18um RF mixed signal 1P6M CMOS process. The first types are 1.8V/1.5V standard current reused topology and second type is current reused with two balance resistors topology VCO. Those topologies have low power-consumption characteristic.
In this thesis, the VCO was designed based on current reused topology. We had finished three chips, that L-band, WiMAX WSC and WiMAX FWA which those are work well except WiMAX FWA chip that has very serious frequency shift problem and it had been discussed in above section. Those chip have good performance which output signal power -4.2 / -8~-10 dBm, power-consumed 1.85mW/3.3mW(with buffer)/6.15mW respectively and under -120 dBc/Hz phase-noise.
5.2 Future Work
Generally, the substrate parameter is major cause of frequency shift problem. In our study, we can make sure 0.1GHz shift at last fitting substrate parameter version but maybe layout skill also influence frequency shift in WiMAX FWA, which is very important and must be considered carefully in related layout.
The Q factor is key parameter of inductance in the design VCO about phase-noise characteristic. For example, the parameter QFWA is Shown in Figure 5.1. The Q factor has been optimized which had good represented on phase noise in chapter 3.The Customize inductor or transformer is different requirement for any different applications.
Figure.5.1 Inductance Q Factor of three Chip
For example, with 4 port and 6 port transform can reduce area and can be used for higher frequency application up to 20GHz. By the way, high Q inductance can be used for filter or VCO. The high Q is the key parameter in the design of VCO circuits. Without a high Q value for the inductor, the circuit performance cannot be improved significantly. Therefore, the design of high quality inductors is a major task for RF application.
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