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Ltp: tft028
version 2.0
16.06.2003
VI TELEFILTER 1. General
Application Note
TFS 211C
1/2
The filter is symmetrical, i.e. input and output are exchangeable with each other. The filter shall be driven single ended. If it is intended to the filter in an balanced environment this can be supported as well. Please contact us for details. 1100 || - 5.1 pF for the input 1100 || - 5.2 pF for the output This impedance is equal for the input and the output. It has to be realized at the point were the filter is mounted. To match this impedance to the impedance of the system a matching circuit is required. The terminating impedances depend on parasitics and q-values of matching elements and the board used, and are to be understood as reference values only. Should there be additional questions do not hesitate to contact our design team. The terminating impedances are :
2. Theoretical matching
The values of the matching elements which are given below are calculated from the terminating impedances. Because these are theoretical values they have to be modified on PCB's corresponding to the existing parasitics.
50 Ohm test circuit
L1 L2
10
5
L3
SAW
L4
1, 2, 3, 4, 6, 7, 8, 9
L1 = L2 = 164 nH L3 = L4 = 180 nH
TELEFILTER GmbH Potsdamer Strae 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.
Ltp: tft028
version 2.0
16.06.2003
VI TELEFILTER 3. Matching on PCB
Application Note
TFS 211C
2/2
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: PCB "tft028" with 50 test circuit
L1 10 5 L2
L3
SAW
L4
1, 2, 3, 4, 6, 7, 8, 9
L1 = L2 = 150 nH L3 = L4 = 120 nH All other components are 0 jumpers. Matching differs slightly between input and output. As long as the resulting difference in termination impedance is low this is an usable way to keep the number of matching elements as low as possible. 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. The strategy to match the filter on the customers board should be as follows: - match the filter according to theoretical values to 50 Ohm. Use your final PCB for this matching to be sure to have the stray elements of the PCB then before. - Adjust matching at filter input and filter output Check VSWR for filter input and output. - Carry out the matching for the actual source and load impedance in three steps. Steps one and two are matching of the filter for input or output to source or load impedance respectively. The result of the matching of the filter input to the actual source can be checked via the VSWR at the filter output which is still matched to 50 Ohms and vice versa. The third step is the matching of the filter input to the actual source and the filter output to the actual load.
In case of questions please contact us to
TELEFILTER GmbH Potsdamer Strae 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.

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