PhaseLocked Loop 1 PhaseLocked Loop in RF Receiver

Phase-Locked Loop 1

Phase-Locked Loop in RF Receiver Antenna BPF 1 LNA BPF 2 Mixer BPF 3 IF Amp Demodulator RF front end LO Ref. PD Loop Filter 1/N VCO Phase. Locked Loop 2

Functional Blocks in PLL Ref PD Loop Filter 1/N VCO LO Phase. Locked Loop • Phase detector (PD): find difference between phases of two signals • Loop filter: provide appropriate control voltage for the voltage-controlled oscillator (VCO) • VCO: generate signals with phase determined by the control voltage • Divide-by-N: LO phase changes N times faster than Ref phase 3

Design Issues • Tracking behavior • Noise performance • Jitter characteristics – Jitter tolerance – Jitter transfer – Jitter generation • Power consumption 4

System Modeling v. Ref • • • PD vd F(s) v. C VCO v. LO v. Ref: input reference signal v. LO: local oscillator (LO) output signal vd: detector output F(s): transfer function of loop filter v. C: control voltage for VCO 5

System Modeling v. Ref q. Ref PD K dq e VCO F(s) v. LO q. LO • • Phase signals contain information q. Ref: phase of reference signal q. LO: phase of local oscillator (LO) signal qe: phase difference between q. Ref and q. LO 6

Jump in Phase 7

Ramp in Phase 8

Ramp in Phase 9

Phase Detector q. REF qe + Kd vd - q. LO • Vd=Kdqe=Kd(q. REF – q. LO) • Kd: gain of phase detector 10

Loop Filter vd F(s) v. C • VC(s) = F(s) Vd(s) • Low-pass filter – Extract phase error – Remove high frequency noises • Passive filter for integrated PLL • Active filter for discrete component PLL 11

Passive Lag Filter R 1 + + vd – R 2 C v. C – • Lag filter: pole magnitude smaller than zero • Passive components: high linearity, gain < 1 12

Active Lag Filter R 1 C 1 R 2 + vd – C 2 + – + v. C – • Can adjust pole and zero locations • Can have gain • Op amp limitations 13

Active Proportional-Integral (PI) Filter R 1 R 2 + + vd – C – + v. C – • Large open loop gain at low frequency • Op amp limitations – Linearity – Noise – Open loop gain 14

Voltage-Controlled Oscillator v. C KVCO + 1/s q. LO + w 0 • KVCO: gain of VCO 15

Transfer Function of PLL w 0 q. REF qe + Kd vd F(s) v. C KVCO + + 1/s q. LO - q. LO • Open-loop transfer function from qe to q. LO 16

Transfer Function of PLL w 0 q. REF qe + Kd vd F(s) v. C KVCO + + 1/s q. LO - q. LO • Closed-loop transfer function from q. REF to q. LO 17

Transfer Function from q. REF to qe w 0 q. REF qe + Kd vd F(s) v. C KVCO + + 1/s q. LO - q. LO • Closed-loop transfer function 18

Other TF of Interest v. Cn q. REF qe + Kd vd F(s) v. C + + KVCO 1/s q. LO - q. LO • Noise in control voltage 19

Other TF of Interest qn q. REF qe + Kd vd F(s) v. C KVCO 1/s + + q. LO - q. LO • Phase noise of VCO 20

Transfer Functions for Different Loop Filters • Passive lag filter • Active PI filter 21

Normalizing Transfer Function • Normalized denominator • Passive lag filter • Active PI Filter 22

Normalized Transfer Function • Passive lag filter • Active PI Filter 23

Normalized Transfer Function • Passive lag filter • Active lag filter 24

Frequency Response of H(s) 25

Frequency Response of He(s) 26

Step Response of PLL • Phase step • Phase Error • Steady state error (final value theorem) 27

Step Response 28

Ramp Response of PLL • Phase ramp • Phase Error • Steady state error (final value theorem) 29

Ramp Response 30

General Steady State Error in Ramp Response • High loop gain • Low loop gain 31

Stability of PLL • Criterion for stability – Closed-loop pole at left half plane – Sufficient phase margin • Control of pole location – Open loop gain – Open loop zero • Check root locus 32

Root Locus Method • Closed-loop TF • Closed-loop poles make – K=0, open-loop poles – K infinity, open-loop zeros or infinity 33

Root Locus for Passive Lag Filter 34

Root Locus for Active Lag Filter 35

Root Locus for Active PI Filter 36

Root Locus for 1 st-Order LP Filter 37

Effects of Parasitics 38

Effects of Zero 39

Phase Noise and Jitter • Phase noise – Fluctuation in phase – Frequency domain – Discussed in RF circuits • Jitter – Error in clock edge (period) – Time domain – Significant in communications circuits • Two concepts – Related to each other – Exact relationship not clear 40

Jitter Measurements Agilent, “Understanding Jitter and Wander Measurements and Standards. ” 41

Jitter Tolerance • Ability of a PLL to operate with jitter – Applied to its reference – Various magnitudes – Different frequencies • Usually specified using an input jitter mask – Jitter magnitude and corner frequencies – BER requirement – Various for standards 42

PLL in Clock and Data Recovery 0 1 0 1 0 1 1 0 0 X 1 0 Ideal signal Distorted signal Ideal clock 0 0 Recovered clock 1 0 0 1 0 43

Jitter Tolerance Mask 44

Jitter Tolerance Measurement 45

Jitter Tolerance Measurement 46

Jitter Tolerance Measurement • Error at corner frequency – Insufficient clock recovery bandwidth – Incorrect mask used 47

Jitter Tolerance Measurement Tolerance margin • Excessive jitter tolerance margin 48

Jitter Tolerance Measurement • Occasional fail at specific frequencies – Need extra settling time after jitter amplitude change • Repeating with additional settling time • Spot measurement 49

Jitter Tolerance Measurement • Limited clock recovery bandwidth • Eye-width alignment noise 50

Jitter Tolerance Measurement • Limited buffer store 51

Jitter Transfer • Jitter transfer or jitter attenuation • Output jitter vs. input jitter – Input jitter with various amplitudes and frequencies – Output jitter measured with various bandwidths • Intrinsic jitter • Typically specified using a bandwidth plot – Amplitude – Roll off speed – Corner Frequency 52

Jitter Transfer Mask 53

Jitter Transfer Measurement • Jitter tolerance mask used to set input jitter level • Sinusoidal jitter at magnitudes and frequencies • Narrow-band measurement 54

Jitter Transfer Measurement • Different test masks • SONET mask: additional amplitude at lower band 55

Jitter Transfer Measurement • Measurement set-up noise • -40 d. B sufficient 56

Jitter Transfer Measurement • Low-frequency phase noise • Power-line crosstalk • Short measurement time 57

Jitter Transfer Measurement • Incorrect filter characteristic • Excessive peaking 58

Jitter Transfer Plot E. Barari, “Jitter Analysis / Specification, ” May 2002. 59

Measured Jitter Transfer Characteristic E. Barari, “Jitter Analysis / Specification, ” May 2002. 60

Measured Jitter Transfer Characteristic E. Barari, “Jitter Analysis / Specification, ” May 2002. 61

Measured Jitter Transfer Characteristic E. Barari, “Jitter Analysis / Specification, ” May 2002. 62

Measured Jitter Transfer Characteristic E. Barari, “Jitter Analysis / Specification, ” May 2002. 63

Jitter Generation • Intrinsic jitter produced by the PLL – Thermal noise – Drift in VCO • Measured at its output – Applying a clear reference signal to PLL – Measuring its output jitter. • Usually specified as a peak-to-peak period jitter value 64

Jitter Generation Standard 65

Jitter Generation Measurement • Direct measurement of p-p jitter • Phase noise measurement • Eye diagram and histogram 66

Jitter Generation Measurement 67

Measurement Considerations • • • Calibration Measurement range Measurement time Power Frequency offset 68

TF from Noise in VCO Control Voltage v. Cn -1 Kd F(s) + + KVCO/s q. LO • Can be viewed as low-pass filter 69

TF from Noise in VCO Control Voltage 70

TF from Phase Noise in VCO qn -1 Kd F(s) KVCO/s + + q. LO • High-pass filter • The same as He(s) 71

Phase Error in VCO v. Cn HC(s) q. REF qe + Kd F(s) KVCO/s qn Hq(s) q. LO - q. LO • v. Cn dominate at low frequencies • qn dominate at high frequencies 72