Ltp: tft025

version 1.0

19.06.2001

Application Note

TFS 321

2/3

TELEFILTER GmbH

Potsdamer Straße 18

D 14 513 TELTOW / Germany

Tel: (+49) 3328 4784-0 / Fax: (+49) 3328 4784-30

E-Mail:

tft@telefilter.com

VI TELEFILTER reserves the right to make changes to the product(s) and/or information contained herein without notice. No liability is

assumed as a result of their use or application. No rights under any patent accompany the sale of any such product(s) or information.

L1 = L2 = 72.6 nH, C1 = C2 = 1.43 pF, L3 = 175 nH

50 Ohm Test circuit 2

1

5

2, 4, 6, 7, 8

SAW

L1

C1

L2

C2

3

L3

The theoretical values of the stated elements are:

C1 = C2 = 3.38 pF, L1 = L2 = 53 nH, L3 = 175 nH

3. Matching on PCB

The theoretical matching was done without consideration of parasitics. The elements which

have to be used on the PCB are slightly different from the stated above.

For example for our PCB with 50

Ω test circuit 1 we had to split the serial inductors in two

elements to get identical results compared to our golden fixture using E12 series inductors.

L1 = 47 nH + 27 nH

L2 = 47 nH + 27 nH

C1 = C2 = 0 pF

L3 = 100 nH

All other components are 0

Ω jumpers.

But if the parasitics on the customer board (mentioned parasitics, additional parasitics of

active parts) are different to this PCB the matching elements have to be slightly adjusted.

Both in line and shunt elements change both pass band tilt and pass band ripple. But

- The in line coils mainly influences the pass band ripple a decrease of the inductance of the

in line coils will decrease pass band ripple or change a round pass band shape towards a

flat one