1. Phase Noise and Amplitude Issues of a Wide-Band VCO Utilizing a Switched Tuning Resonator
Ali Fard M¨alardalen University, Dept. of Computer Science and Electronics, V¨aster°as, P.O. Box 883 SE , Sweden, “Phase noise and amplitude issues of a wide-band VCO utilizing a switched tuning resonator,” Circuits and Systems, ISCAS IEEE
教授：林志明　教授
學生：劉彥均

2. Outline Introduction General oscillator design considerations
Wide-band VCO design
Resonator design and prediction of the output amplitude
Phase noise
Measurements
Conclusion

3. Introduction(1)
Demands for transceivers operating in frequency ranges from 0.9 to 6 GHz.
Support multiple radio standards operating over a wide frequency range with minimal amounts of duplicate hardware.

4. Introduction(2) Voltage Controlled Oscillator (VCO) is
identified as one of the limiting factors in
tuning range, silicon area, power consumption and the primary source of noise.

5. Introduction(2)
A wide-band VCO employing a switched capacitor resonator is investigated.

6. General oscillator design considerations(1)
In LC-type resonator based oscillators,active devices are used to generate a negative resistance to cancel the losses and providing the conditions for oscillation.

7. General oscillator design considerations(2)
If the negative resistance is too large it may contribute with excess thermal noise and thus deteriorate the phase noise.

8. General oscillator design considerations(3)
Noise is dominated by the tank Q and the oscillation amplitude.
For a given transconductance cell an optimum in phase noise is achieved as long as the output amplitude is a linear function of the tank current and Q.

9. Wide-band VCO design(1)
Simplified VCO circuit schematic with a discrete switched tuning

10. Wide-band VCO design(2)
Circuit schematic of the differential SCA.

11. Wide-band VCO design(3)
The on-state resistance, degrading the overall Q of the resonator.
Parasitic capacitance from the switches during their off-state reduces the maximum achievable oscillating frequency, also has negative impact on the amplitude.

12. Resonator design and prediction of the output amplitude(1)
Since the VCO is designed to operate in the current limited region [2], the output amplitude is roughly given by

13. Resonator design and prediction of the output amplitude(2)
How to design SCA?
The minimum operation frequency is given by the maximum capacitance according to:

14. Resonator design and prediction of the output amplitude(3)
Assume here that a fixed varactor gain is desired within the entire tuning range(we may ignore the varactors and the parasitic capacitance involved)

15. Resonator design and prediction of the output amplitude(4)
Drain parasitic capacitance of the switches during their off-state (sizes of the switches be found)

16. Resonator design and prediction of the output amplitude(5)
The equivalent parallel resistance of the resonator may be expressed as
n has an important impact on the relative variations determining the amplitude variations across the tuning range.

17. Phase noise
The lowest phase noise performance could be achieved by finding a ratio between the PMOS and NMOS transistors that minimized their relative noise contributions and also satisfying the startup conditions.

18. Mesurement(1)
Chip photo of the 0.85 x 0.55 mm 0.18μm CMOS VCO.

19. Mesurement(2)
Measured phase noise at 3.8GHz, 4.5 GHz,5.3GHz.

20. Mesurement(3)
Several phase noise measurements were performed at different carrier frequencies all indicating that the optimum bias point is around mA from 1.5 V supply.

21. Conclusion
A highly flexible wide-band CMOS VCO, utilizing switched tuning was presented.
Power consumption of 6mW, 1.8GHz tuning range, phase noise levels of less than -115 dBc/Hz at 1 MHz offset
Suited for high data rate multi-standard radios.