SI4734 Просмотр технического описания (PDF) - Silicon Laboratories

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SI4734

Si47XX ANTENNA, SCHEMATIC, LAYOUT, AND DESIGN GUIDELINES

Silicon Laboratories 

AN383

Loop Antenna

PCB

AM Front End

Vant

Lant

R P-ant

C ant

CPCB

R de-Q

C tune

R P C -tu ne

RLNA

CLNA

Figure 42. AM Front-end with Series Antenna

and On-chip Resistances Converted to Parallel

Resistances

The circuit can be further simplified because at

resonance RDe-Q and Ctune are fixed and the resistance

and capacitances can be lumped together. The new

circuit is shown in Figure 43.

Lant

Vant

CTotal

RTotal

Where:

1/RTotal = 1/RP-ant + 1/Rde-Q + 1/RPC-tune + 1/RLNA

CTotal = Cant + CPCB + Ctune + CLNA

Figure 43. Circuit Elements have been Lumped following:

Together to Simplify Circuit Further

Analyzing this circuit is a mathematical exercise and is

not covered in this document. It can be easily shown

that the resonant frequency for this circuit is equal to the

resonance

=

--------------1---------------

LantCTotal

Equation 9. Resonant Frequency Calculation

The Q of the circuit at resonance can be calculated by

finding the magnitude of the transfer function and

substituting  with resonance. The Q of the circuit at

resonance is expressed as follows:

Qcircuit = RTotal C---L--T--a-o-n--t-ta---l

Equation 10. Overall Circuit Q Calculation

66

Rev. 0.8

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