Loop Bandwidth Loop bandwidth=Kvco RC 2πfeo C+C2+C3 Kvco and fyco are two factors affecting loop bandwidth Maintain loop bandwidth Output frequency fco varies greatly across the wide range,but Icp also is tuned to compensate fyco >Kyco is maintained Then the loop bandwidth is adaptively controlled across the whole frequency range 2009 IEEE International Solid-State Circuits Conference 2009 IEEE 6
© 2009 IEEE International Solid-State Circuits Conference © 2009 IEEE 6 Loop Bandwidth • KVCO and fvco are two factors affecting loop bandwidth • Maintain loop bandwidth ¾ Output frequency fvco varies greatly across the wide range, but ICP also is tuned to compensate fvco ¾ KVCO is maintained ¾ Then the loop bandwidth is adaptively controlled across the whole frequency range CP VCO ref 1 1 vco 1 2 3 Loop bandwidth 2 = ⋅ + + IK f R C πf CCC
Simplified LC-tank of Multiband VCO Switched capacitors and Vosc+ Vosc- 00001 switched varactors are both Capacitor array adjusted simultaneously with different values of units to maintain both Kyco and 1C25Cn2502550 band steps a~a255 and B~B255 are programmed coefficients YC. 米 See [Lu,et al.,IEEE RFIC Symp.,2008] B2sc米 Varactor array Only LC-tank depicted 2009 IEEE International Solid-State Circuits Conference 2009 IEEE
© 2009 IEEE International Solid-State Circuits Conference © 2009 IEEE 7 Simplified LC-tank of Multiband VCO • Switched capacitors and switched varactors are both adjusted simultaneously with different values of units to maintain both KVCO and band steps • α1 ~ α255 and β1 ~ β255 are programmed coefficients • See [Lu, et al., IEEE RFIC Symp., 2008] f 1 f ctrl osc+ oscen1 255 f f 1 f 255 f en255 v v 1 v 1 v en1 255 v 255 v en255 B ctrl B ctrl LC
Multiband VCO Calibration Using AFC The purpose of AFC is to select the sub-band of VCO whose center frequency is closest to the target frequency automatically Frequency middle 255 k+1 k △f k-1 Compare the distance ftarget and choose the nearest point to the middle! Linear Range (AVc)Vctrl Vclo Vchi 2009 IEEE International Solid-State Circuits Conference 2009 IEEE 8
© 2009 IEEE International Solid-State Circuits Conference © 2009 IEEE 8 Multiband VCO Calibration Using AFC • The purpose of AFC is to select the sub-band of VCO whose center frequency is closest to the target frequency automatically