CHAPTER 3 LC TANK OSCILLATOR THEORY
3.3 Dual band LC VCO
3.3.3 Switched Inductance
Switched resonators circuit compare to conventional dual band VCO circuit, less power consumption and smaller die area. But switched resonators circuit still needs two inductor, so I have a new idea to use an inductor achieving two inductance.(Figure3.9)
Switch Metal6(2finger)
Metal5(4finger)
Figure 3.9Switched Inductance diagram
When switch off, the inductance seems to Tsmc 0.18um four fingers spiral inductor.
When switch on, the inductance seems to Tsmc 0.18um two fingers spiral inductor.
But when switch on (two fingers), we must think about the MOS parasitic resistance the mutual inductance between inner circle and outer circle. So my method is using RF model from Tsmc to import Ansoft Designer and run EM analysis. But we still consider MOS switch parasitic capacity and resistance. RF MOS model is as Figure3.10.
Rg
So MOS main parasitic capacity is approach (C1//C3)+C2.And MOS main parasitic resistance is approach Rd+Rs
If we decide MOS size, then we can estimate C1,C2,C3,Rd,Rs value approximately. So we include these informations in our circuit design. My circuit is a conventional cross-couple type(Figue3.11) to generate negative resistance to cancel resistance because of LC tank unlimited Q value.
R1
First we want varactor C2 to have maximum variable capacitance. Because we must control C2 both sides voltage to make sure capacitance, then we add C1 so C2 both sides voltage doesn’t change with oscillator. If we want C2 to dominate capacitance, the C1 capacitance must be biggest as we can accept.R1, R2 also must be large enough so it seems AC open. We use a NMOS and give voltage from it’s gate to make a current source and control current. Output buffer exist for signal isolation between LC tank and measure instrument.
Signal in
Signal out
Figure 3.11 Output buffer
We adopted a fixed current source and common-drain architecture. A fixed current source can avoid that output buffer current changes with signal in. If the output buffer current changes with signal in, the signal out power can’t export stably.
CHAPTER 4
Figure 4.1 Switch off (4 finger inductance) phase noise
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
Figure 4.2 Switch off (4 finger inductance) tuning range freq. tuning range2.2GHz~2.45GHz
m1noisefreq= Figure 4.3 Switch on (2 finger inductance) phase noise
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
Figure 4.4 Switch on (2 finger inductance) tuning range freq. tuning range4.8GHz~6GHz
output buffer swing=0.4V
total power(include output buffer)=3.8mA*1.8V
4.2 Measurement
Figure 4.5 Switch off (4 finger inductance) phase noise
Figure 4.6 Switch off (4 finger inductance) tuning range
Figure 4.7 Switch on (2 finger inductance) phase noise
Figure 4.8 Switch on (2 finger inductance) tuning range freq. tuning range4.2GHz~5.4GHz
output buffer swing=0.38V
total power(include output buffer)=4.2mA*1.8V
Figure 4.9 Layout
CHAPTER 5
VCO DESIGN FLOW
5.1 Design procedure
The simulation software Spectre RF is used to design analogy circuit. After the layout of the circuit is finished, the LPE (layout parameter extraction) is done to extract parasitic components which is put into the circuit and we simulated complete circuit again.
System Spec
5.2 Test procedure
Measurement of output spectrum and output power performances were obtained using an Adventest R3162 spectrum analyzer.
Power Supply
Ammeter
Die under PCB broad Spectrum Analyzer
Figure 5.2 Experimental set-up
On-board measurements of output spectrum and output power performances were obtained using an Adventest R3162 spectrum analyzer.
CHAPTER 6 CONCLUSION
In first band (switched off,2.2~2.45G),simulation meets measurement mostly, but in measurement spectrum signal isn’t pure. Because my PCB board transmission line width is matching for 5GHz (26mil in 5GHz, S11=-28dB), so spectrum in 5GHz is much pure than 2GHz (26mil in 2GHz, S11=-13dB). Spectrum in 5GHz, we can see the appearance of tuning range shift. Because we ignore inductor’s outside metal of the inner circle when switch on. This also has inductance and generates mutual inductance with inner circle. So these reason made real inductance over exception.
And switch’s parasitic also effects Q value of inductor, so phase noise in measurement is higher than simulation.
Compare with report before[20]
Parameter Dual band
-125dBc/MHz -123dBc/MHz -118dBc/MHz -106.3dBc/MHz
Die
Size(mm^2)
1.3x0.69 1.3x0.69 1.38x0.77 1.38x0.77
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Vita and Publication
姓 名: 楊岱原
出生日期: 中華民國七十年八月十四日 學經歷:
國立成功高級中學 (86 年9 月~89 年6 月)
國立交通大學電子工程學系 (89 年9 月~94 年6 月) 國立交通大學電子研究所碩士班 (94 年9 月~96 年7 月)
發表著作:
1. H. L. Kao, D. Y. Yang, Albert Chin, and S. P. McAlister, “2.4/5 GHz Dual-Band LC VCO using Variable Inductor and Switched Resonator,” IEEE MTT-S Int’l Microwave Symp. Dig., pp., June 12-17, 2007.