A Dynamic GHz-Band Switching Technique for RF CMOS VCO K, Shibata. ; H, Sato. ; N, Ishihara. ; Silicon Monolithic Integrated Circuits in RF Systems, 2007 Topical Meeting on Jan.10-12 2007 Page(s):273 - 276 積體電路設計研究所 指導教授 : 林志明 教授 學生 : 郭峻瑋

Outline Abstract Introduction Conventional VCO VCO circuit using simultaneous LC switching Experimental results and discussions Conclusion

Abstract To get wide band switching, it has been clarified analytically that keeping Q constant is important to configure the circuit. a dual band VCO circuit has been designed by using a 0.13-μm standard CMOS process technology and succeeded in switching the band dynamically from 2 to 4 GHz .

Introduction A circuit which can switch capacitors and inductors simultaneously has been suggested. The chip fabricated was operated with a power supply voltage of 1.7 V.

Conventional VCO Fig. 1. Conventional LC-VCO circuit.

Where L: inductance for resonation, Cc: constant capacitance setting the operation band, Cvo: varactor capacitance, C0: total capacitance. Value of Q is decreased by increasing value of Co.

VCO circuit using simultaneous LC switching Fig. 2. Simultaneously LC switching VCO circuit.

Quality factors Q of those operating conditions are expressed following equations respectively. If loss resistance values of r1ow and rhigh are the same, a condition of keeping Q constant is

Loss resistances are expressed by following equations respectively. If L1 is equals to L2 to simplify the discussion, a condition that r1ow becomes equal to rhigh to keep value of Q constant is

Fig. 3. Equivalent circuit considered loss resistances. Low frequency (SW1: ON, and SW2: OFF). High frequency (SW1: OFF, and SW2: ON). Fig. 3. Equivalent circuit considered loss resistances.

Fig. 4. Resonant frequency switching characteristics simulated.

Experimental results and discussions Signal output buffers which can drive 50 Ω are added to the core LC-VCO circuit. The sizeis 1.8 mm x 1.7 mm. The chip packaged was measured by using a spectrum analyzer.

Fig. 5. VCO circuit fabricated.

Fig. 6. Microphotograph of the VCO chip.

Fig. 7. Oscillation frequency versus control voltage.

Fig. 8. Characteristics of Phase Noise.

FOM and FOMT, were calculated using following equations. L{Δf } is measured phase noise at the frequency offset Δf from the carrier at fo, and PDC is the measured dc power dissipation in mW. And, FTR is frequency tuning range.

Conclusion