L2572

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

12 of 14

www.unisonic.com.tw

QW-R102-032.A

DESIGN OF PLL LOOP PARAMETERS

The UTC L2572 is normally used as a type 1 second order loop and can be represented by the above diagram.

For such a system the following parameters apply;

and

2

0

1

n

D

K

K

ω

n

ω

ζ

τ

2

where:

ξ is the loop damping factor

R1 is loop amplifier input impedance

From these factors the loop 3dB bandwidth can be determined from the following expression;

1

)

1

2

(

)

1

2

(

2

2

2

2

2

2

3

+

+

±

+

=

ζ

ω

ζ

ω

ω

n

n

dB

Which approximates to

n

dB

ω

ω

2

3

=

when

2

1

=

ζ