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ADF4193

Low Phase Noise, Fast Settling PLL Frequency Synthesizer

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BASED ON

A 10s Fast Switching PLL Synthesizer for a GSM/EDGE

Base-Station

ByMike Keaveney, Patrick Walsh,

Mike Tuthill, Colin Lyden, Bill Hunt

ISSCC 2004 / SESSION 10 / CELLULAR SYSTEMS AND BUILDING BLOCKS / 10.6

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FUNCTIONAL BLOCK DIAGRAM

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50Ω

52Ω

No connection here

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FEATURES• New fast settling fractional-N PLL architecture• Single PLL replaces ping-pong synthesizers• 0.5 degree RMS phase error at 2 GHz RF output• Digitally programmable output phase• RF input range up to 3.5 GHz• 3-wire serial interface• On-chip low noise differential amplifier• Phase noise figure of merit –216 dBc/Hz• Loop filter design possible using ADI SimPLL

APPLICATIONS• GSM/EDGE base stations• PHS base stations• Instrumentation and test equipment

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Background – GSM Base-station Synthesizer Requirements

• Switch frequency in 10s => Wide PLL BW

• Low Phase Noise during Data Burst• Low Spurious during Data Burst } => Narrow PLL BW

547s30s

Tx @ f2Tx @ f1 Tx @ f3

PA o/p power

~10s for Tx Synth. to switch

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Phase Noise & Lock Time Simulations

320kHz BW:Lock Time: 6.3s

5 s/div.

1805

1880

0 5 10 15-50

0

50

40kHz Loop BW:Lock Time: 120s

No cycle slip ifBW>0.8*Fstep/2N[Cicero JSSC’00]

Ph

ase

(Deg

.)F

req

ue

ncy

(M

Hz)

50 s/div.

0 50 100 150-50

0

50

1805

1880

Ph

ase

No

ise

(d

Bc

/Hz)

1kHz 1MHz

-140

-100

N=1880/1040.8*75M/(2N)=528k

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8x Bandwidth Switching

NF(s)IK CPV

..

2Gain Loop

Wide BW: 64x ICP & R/8Narrow BW: 1x ICP & R

0dB

36dB

-180o

-135o

8f0f0

[Ref: Crowley ‘78]

64x ICP

1x ICP

N

Charge Pump Cell Array,ICP<63..0>

CP

CZ

R/8

7R/8

FoutPFD

Fref sKV

PLL Static Phase Error

At Balance: ICP = ICP

5º @ 1.85GHz 7.5ps ( 0.065º @ 26MHz)

With = 3ns, for < 7.5ps, requires ICP mismatch < 0.25%

Charge Balance:

Fref

Fdiv

Matched

UPDOWN

Mismatched

ICP ICP +ICP

-ICP

10

64x → 1x ICP

mismatch = 10%

= 200°

IdealTime (5s / div.)

ICP Envelope

Conventional Charge Pump PLL

1x0 64x

N

PFD

ICP<63..0>UP

DN

200°/div.

0

Output Phase (simulation)

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Differential Charge Pump Concept• Better Up/Down Matching

– Same Type Devices

– Symmetric Layout

• Charge Injection is Common Mode to Vtune

• Requires– Low Noise Diff-amp

– CMFB

• Matching improved but still residual mismatch due to process ( ~= 0.5%)

Vbias2

DNn

UPp

Vbias1

UPn

DNp

CPO+ CPO–

Vtune

+ –

mp1 mp2

mn1 mn2

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Charge Pump Cell with Chopped Outputs

Vbias1

UPp1

mp1

DNp2 DNp1

mp2

UPp2

Vbias2

DNn1

mn1

UPn2 UPn1

mn2

DNn2

CPO+ CPOB–~2V ~2V

5V

Fref

UP1,DN1UP2,DN2

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Chopped Up/Down Signal Paths from PFD

Chopped Output Charge

Fref

Fdiv

D QRB

D QRB

UP1, DN2

DN1, UP2

Fref

Fdiv

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Diff-Amp

• PLL suppresses DC errors & 1/f noise.

• Want zero IIN mismatch MOS i/p’s

• Noise > 40kHz → FM sidebands < 7nV/Hz required @ Vout

-130

-100

Phase Noise

40kHz

CPO –

CPO +Vref

Vout

5mA5mA

10000.5

500 500

500 500

–+

10000.5

• Pulse Stretch circuit → Fast leading edge, current controlled trailing edge → Control current mirrored to both up and down pulses.

Common Mode Feedback Loop

UP

DN

CPO+

CPO–

UPpDNp

UPnDNn

UPDN

+–

+–~2V

200A

ChargePump

+

_PFD

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UPDN

UPpDNp

} from PFD

UPnDNn

CMFB Pulse Stretch Signals

} to PMOS switches

} to NMOS switches

Differential CP output

Common Mode output

Phase info from PFD remains intact

Proposed Fast Locking PLL

Fref

FoutD

D

ChargePump<64:1>

Mod-130

2C1

R2/16

2C2

7R2/16

2C1

R2/16

2C2

7R2/16

÷ N / N+1

Fast LockControl

–+

C3

R3

External

External

+

–

R3/7

Open R2 & R3 switches when ICP is @ 1x

ICP Reduction with Compensation

MUX10

X2

Z-1

2

+

FRAC Out

X2

+–+

1

+1

3

3

130

16

0

X2

ICP

(mA)

Fref

17 18Time (µs)

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Measured: Phase Lock Time

75 MHz jump from 1880 to 1805 MHz

Time (s)

Pha

se (

De

gre

es)

-25

-15

-5

5

15

25

-10 10 30 50 70 90 110 130 150

Start

Chopping Off vs. Chopping On

Measured:~1% ICP mismatch change 20° phase step w/o chopping

-40

-20

0

20

40

-10 10 30 50 70 90

Time (s)

WideBW

NarrowBW

Pha

se (

De

gre

es) Chopping Off

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Fout = 1860MHz, Fref = 26MHz, Chopping @ Fref/2External VCO (Vari-L 1843T)

Measured: Output Phase Noise

DCS-1800 Tx LO Mask

dBc/

Hz

RMS Phase Error (SSB) = 0.25°

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Chopping @ Fref/2, (with 2% measured ICP mismatch)

Measured: Spur Side-Band Levels

Fout = 1872.4 MHz (N = 72 2/130)

-100

-80

-60

-40

-20

0

1872 1877 1882 1887

Frequency (MHz)

dBc

Integer Boundary Spurs:-75dBc @ f = +/- 400kHz

Chopping:<-95dBc @ f = 13MHz

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Die Photo

ChargePumpArray

Modulator

N

PFD

SerialInterface

Tim

ers

&C

ontr

ol

Diff-Amp

CMFB

BGR

R

LockDetect Loop

FilterSwitches

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Lock Time 10 s

RMS Phase Error 0.25 deg.

Idd: Charge Pump (5V) 33 mA

Diff-amp (5V) 30 mA

Remainder of chip (3V) 20 mA

Fractional Spurs (worse case at integer boundaries):

-75 dBc @ 400kHz

-85 dBc @ 600kHz

Spur due to Chopping @ Fref/2:

Reference Spur:

< -95 dBc @ 13MHz

< -95 dBc @ 26MHz

Chip Size 2.29 x 2.32 mm

Technology 0.35 BiCMOS w/ 5V options

Package 5x5mm 32 lead LFCSP

Performance Summary

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Summary• Static Phase Error due to Up to Down Mismatch

in the PFD and Charge Pump blocks can be eliminated using a chopping scheme.

• Loop Gain Changes during BW switching can be digitally compensated for in the Modulator.

• A PLL based synthesizer can jump over the full TX band in <10s and still meet the phase noise and spurious requirements for a GSM and EDGE base-station.