MK1574

Frame Rate Communications PLL

MDS 1574-01 D

4

Revision 011999

Printed 11/15/00

MicroClock Division of ICS • 525 Race Street • San Jose • CA • 95126•(408)295-9800tel•(408)295-9818fax

I C R O

The series-connected capacitor and resistor between CAP1 and CAP2 (pins 4 and 6) determine the dynamic

characteristics of the phase-locked loop. The capacitor must have very low leakage, therefore a high quality

ceramic capacitor is recommended. DO NOT use any type of polarized or electrolytic capacitor. The series

connected capacitor and resistor between CAP1 and CAP2 (pins 4 and 6) determine the dynamic

characteristics of the phase-locked loop. The capacitor must have very low leakage, therefore a high quality

ceramic capacitor is recommended. DO NOT use any type of polarized or electrolytic capacitor. Ceramic

capacitors should have C0G or NP0 dielectric. Avoid high-K dielectrics like Z5U and X7R; these and other

ceramics which have piezoelectric properties allow mechanical vibration in the system to increase the output

jitter because the mechanical energy is converted directly to voltage noise on the VCO input.

The values of the RC network determine the bandwidth of the PLL. The values of the loop filter components

are calculated using the constants K1 and K2 from the table on page 5. The loop bandwidth is set by the

capacitor C and the constant K1 using the formula

The loop damping is set by the resistor R, the capacitor C, and the constant K2 using the formula

ζ (zeta) is the damping factor

For example, to design the loop filter when generating 8.192 MHz from 8 kHz:

1. From the table on page 2, the address is E. The table on page 5 shows constants K1=0.0516 and K2=6.2.

2. A good value for the loop bandwidth is 1/20 the input frequency; where 8 kHz/20 = 400 Hz. Using

Equation 1,

Therefore,

3. A good value for the damping factor

ζ is 0.707. From Equation 2,

R =

C

ζ • K2

R =

0.707 • 6.2

16E-9

= 34.7 k

Ω (36 kΩ nearest standard value)

Loop Bandwidth and Loop Filter Component Selection

Equation 1

BW (Hz) =

C

K1

400 =

C

0.0516

C =

400

0.0516

(