Definition of loop Bandwidth Open-loop cut-off frequency is selected as loop bandwidth,but not intuitively Loop gain is a good substitute For typical third-order PLL with second-order passive filter,loop gain can be expressed as BW=lrKvcoR1.bKvcoR1 b>10) 2TTN b+1 2TTN Kyco and N are variables RFIC-Atlanta June 15-17,2008 6RFIC – Atlanta June 15-17, 2008 6 Definition of loop Bandwidth • Open-loop cut-off frequency is selected as loop bandwidth, but not intuitively • Loop gain is a good substitute • For typical third-order PLL with second-order passive filter, loop gain can be expressed as • KVCO and N are variables ⋅ ≈ CP VCO 1 CP VCO 1 IK R IK R b BW= (b>10) 2πN b+1 2πN