LECTURE 040 –DIGITAL PHASE LOCK LOOPS (DPLLs)

Lecture 040 – Digital Phase Lock Loops (DPLLs) (09/01/03) Page 040-41Flowchart of the DPLL Design ProcedureYesUse EXORYesAre there missing edges?Specify the noise bandwidth, B LDesign the VCOSpecify the range of f 1 and f 2Determine N or range of NDetermine ζ or range of ζNoIs Noise Suppression Required?NoChoose the PFD, design the VCO and the loop filterUse PFDTP Given T P , ∆ω po , or T L∆ω T po LUse T P to find τ 1 or τ 1 +τ 2Use ∆ω po and ζ to find ω n Use T L to find ω nEstimate ω n from τ 1Use ω n and ζ to find τ 1Use B L and ζ to find ω nSelect the loop filter and determine τ 1 , τ 2 , (K a )Use ω n and ζ to find τ 2Calculate the loop filter values Fig. 2.2-37CMOS Phase Locked Loops © P.E. Allen - 2003Lecture 040 – Digital Phase Lock Loops (DPLLs) (09/01/03) Page 040-42Design Example – A Frequency Synthesizer Using the 74HC/HCT4076Design a DPLL frequency synthesizer using the CMOS 74HC/HCT4076 PLL. Thefrequency sythesizer should be able to produce a set of frequencies in the range of 1MHzto 2MHz with a channel spacing of 10kHz. Use a PFD and a passive lag-lead filter.Design:1.) Determine the ranges of the input and output frequencies.f 1 is constant at 10kHz. f 2 (min) = 1MHz and f 2 (max) = 2MHz2.) Choose N.N max = 2MHz10kHz = 200 and N min = 1MHz10kHz = 100∴ N mean = N max·N min = 1413.) Find ζ. Start by choosing ζ = 0.7 and find ζ max and ζ min .ζ maxζ max=N maxN min= 2 and ζ = ζ max·ζ min = 0.7∴ ζ 2 min 2 =0.49 → ζ min = 0.59 and ζ max = 0.59 2 = 0.83∴ 0.59 < ζ < 0.83 which is consistent with our choice of ζ.4.) Select the PFD as the phase detector. For the 74HC/HCT4076, V OH = 5V andV OL =0V. This gives a K d = 5V/4π = 0.4 V/rad.CMOS Phase Locked Loops © P.E. Allen - 2003