PLL Intro - Raffia.ch

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Purdue University EET 257 Power & RF Electronics

Intro to the Phase Locked Loop

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u Basic Block Diagram

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u Basic Block Diagramu diagram operation

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u Phase Detector

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u Phase Detectoru xor CD4046 phase II

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u Loop Filter

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u Loop Filter

u VCO

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Op Amp vs Phase Locked Loop

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u inputs:NI & INV input & feedback

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u output: voltage freq (or phase)

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u -fb => VINV = VNI -fb => ffb = fin

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u v div in -fb => volt x freq div => freq x

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u v div in -fb => volt x freq div => freq x

u very robust wrt V very robust wrt f– self correcting self correcting

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Basic Block Diagram

sine

square

voltagecontroloscill.

DClowpass

filter

squarephasedetector

feedback

inputsquare

wave optional

Figure 6-39 page 323

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Basic Block Diagram

sine

square


DC

lowpass

filter

squarephase

detector

feedback

inputsquarewaveoptional

digital

digital

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Basic Block Diagram

sine

square


DC

lowpass

filter

squarephase

detector

feedback


- feedback

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Basic Block Diagram

sine

square


DC

lowpass

filter

squarephase

detector

feedback

input

squarewaveoptional

same freq

fixed phasedifference

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Basic Block Diagram

sine

square


DC

lowpass

filter

squarephase

detector

feedback


frequency

follower

Assuming that the loop is locked ffb = fin.

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Basic Block Diagram

sine

square


DC

lowpass

filter

squarephase

detector

feedback


Average value proportional to phase difference betweenfin and ffb.

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Basic Block Diagram

sine

square


DC

lowpass

filter

squarephase

detector

feedback


Steady DC proportionalto phase difference betweenfin & ffb

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Basic Block Diagram

sine

square


DC

lowpass

filter

squarephase

detector

feedback


frequency & phase proportional to VDC in

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Effects of Variations

sine

square


DC

lowpass

filter

squarephase

detector

feedback


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Overview



u Loop Filter

u VCO

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Phase DetectorDigital output:

aveage value is proportional to the difference in phase between fin and ffb.

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Phase DetectorDigital output:

aveage value is proportional to the difference in phase between fin and ffb.

Exclusive ORinput feedback output0 0 00 1 11 0 11 1 0

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XOR phase detectorFigure 6-40 a, b, c page 325

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Transfer Funtion (Math)

V Vt

TAVE pkon= typical pulse width modulation equation

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V Vt

TAVE pkon= typical pulse width modulation equation

t

Ton =

°θ

180

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typical pulse width modulation equation

V Vout ave hi=°

θ180

output voltage proportional tothe difference in phase

V Vt

TAVE pkon=

t

Ton =

°θ

180

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What if fin < or > ffb ?

Figure 6-42 a & b

page 328

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XOR phase detectorFigure 6-42 a, b page 327

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XOR phase detectorFigure 6-42 a, b page 327

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CD4046 phase II detector

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u considerable additional logic

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u fin > ffb => Vout high most of each cycle– rest of each cycle Vout is open

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u fin < ffb => Vout ground most of each cycle– rest of each cycle Vout is open

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u phase of fin leads => vout high while leading

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u phase of fin leads => vout high while leading

u phase of fin lags => vout gnd while lagging

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Overview



u Loop Filter

u VCO

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Low Pass Filter

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Low Pass Filter

u digital in; DC out

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Low Pass Filter


u simple RC is usually OK

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Low Pass Filter



u slow => very little ripple => stable freq

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Low Pass Filter




u slow => sluggish response to changes

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Low Pass Filter





u fast => quick response to upsets

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Low Pass Filter





u fast => quick response to upsets

u fast => ripple on output => variation in freq

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What size RxC ?

Laplace, closed loop analysis:

1τ s

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What size RxC ?


1τ s

G s H s

G s H s

( ) ( )

( ) ( )1 +

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What size RxC ?


1τ s

G s H s

G s H s

( ) ( )

( ) ( )1 +

Must know transfer function [G(s) & H(s)] of phaseII detector and VCO

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Simplier: Heavily overdamped

τ = ≈RCT

ripplelongest50%

%

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Overview



u Loop Filter

u VCO

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CD4046 Voltage Controlled Osc

GND

8

+V

16

RT

11

INHIB

5

CT

7

CT

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VCO OUT 4

PH 1 2

PH 2 13

VCO IN9

SIG IN14

- FB3

4046

VDD

VoutVin

Ct Rt

Figure 6-41page 327

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GND

8

+V

16

RT

11

INHIB

5

CT

7

CT

6

VCO OUT 4

PH 1 2

PH 2 13

VCO IN9

SIG IN14

- FB3

4046

VDD

VoutVin

Ct Rt

5V - 15V

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GND

8

+V

16

RT

11

INHIB

5

CT

7

CT

6

VCO OUT 4

PH 1 2

PH 2 13

VCO IN9

SIG IN14

- FB3

4046

VDD

VoutVin

Ct Rt

Turns part ON.

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GND

8

+V

16

RT

11

INHIB

5

CT

7

CT

6

VCO OUT 4

PH 1 2

PH 2 13

VCO IN9

SIG IN14

- FB3

4046

VDD

VoutVin

Ct Rt50pF - 1µµF

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GND

8

+V

16

RT

11

INHIB

5

CT

7

CT

6

VCO OUT 4

PH 1 2

PH 2 13

VCO IN9

SIG IN14

- FB3

4046

VDD

VoutVin

Ct Rt5kΩ − 1Ω − 1MΩΩ

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GND

8

+V

16

RT

11

INHIB

5

CT

7

CT

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VCO OUT 4

PH 1 2

PH 2 13

VCO IN9

SIG IN14

- FB3

4046

VDD

VoutVin

Ct Rt

Square wave 50% duty cycle1Hz to > 1MHz

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Overview



u Loop Filter

u VCO

PLL Intro - Raffia.ch

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