AN3394 datasheet(23/29 Pages) STMICROELECTRONICS

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AN3394

Demonstration of C11 and C22 calculation

Doc ID 018754 Rev 5

23/29

Appendix A

Demonstration of C11 and C22 calculation

A.1

Equivalent circuit

Ztot defines the input impedance of the matching circuit and the equivalent parallel antenna.

Figure 22.

Final equivalent circuit

Calculation of Req:

Equation (A.I.1)

Calculation of Ztot:

Equation (A.I.2)

Resonance pulsation:

To determine the resonance pulsation, the imaginary part of Ztot must be cancelled. The

conditions are:

Equation (A.I.3)

RXP

--------------------------------

tot

---------------------------

11 )

(

–

() j ω L

eq 1LPA

–

() j ω L

------------------------------------------------------------------------------------------------------------------------------

tot

out

and

tot

()

–

()

–

()

–

()

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

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