TLC2943

HIGH-PERFORMANCE DUAL PHASE-LOCKED BUILDING BLOCK

SLAS249 – NOVEMBER 1999

21

POST OFFICE BOX 655303

APPLICATION INFORMATION

Using the lag-lead filter in Figure 19(b) and divider N value, the transfer function for phase and frequency are

shown in equations 4 and 5. Note that the transfer function for phase differs from the transfer function for

frequency by only the divider N value. The difference arises from the fact that the feedback for phase is unity,

while the feedback for frequency is 1/N.

Hence, the transfer function of Figure 19(a) for phase is

F2(s)

F1(s) +

Kp

K

V

N

(T1

) T2)

1

) s

T2

s2

) s 1 )

Kp KV T2

N

(T1

)T2) )

Kp KV

N

(T1

)T2)

(4)

and the transfer function for frequency is

F

OUT(s)

F

REF(s)

+

Kp

K

V

(T1

) T2)

1

) s

T2

s2

) s

1

)

Kp KV T2

N

(T1

)T2) )

Kp KV

N

(T1

)T2)

(5)

of equation (4) and (5) with the standard 2-pole denominator gives the following results.

wn +

Kp

K

V

N

(T1

) T2)

Solving for T1 + T2

T1

) T2 +

Kp

K

V

N

w 2

n

(6)

and by using this value for T1 + T2 in equation (6) the damping factor is

z +

wn

2

T2

)

N

Kp

K

V

solving for T2

T2

+

2

z

w –

N

Kp

K

V

then by substituting for T2 in equation (6)

T1

+

K

V

Kp

N

w 2

n

–

2

z

w

n

)

N

Kp

K

V

(7)

(8)

(9)