MAS9079 Просмотр технического описания (PDF) - Micro Analog systems

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MAS9079

AM Receiver IC

Micro Analog systems 

DA9079.003

19 May, 2005

ANTENNA TUNING CONSIDERATIONS

The ferrite bar antenna having inductance LANT and

parasitic coil capacitance CCOIL is tuned to three

reception frequencies f1, f2 and f3 by parallel

capacitors CANT1, CANT2 and CANT3. The receiver

input stage and internal antenna capacitor switches

have capacitances CRFI1, COFF2, COFF3 which affect

the resonance frequencies. COFF2 and COFF3 are

switch capacitances when switches are open.

When switches are closed these capacitances are

shorted by on resistance of the switches and they

are effectively eliminated. Following relationships

can be written into three tuning frequencies.

Frequency f1 (highest frequency):

CTOT1=CCOIL+CANT1+CRFI1+COFF2+COFF3=CCOIL+CANT1+6.5pF+24pF+75pF3=CCOIL+CANT1+105.5pF,

f1 = 2π

1

L ANT ⋅ CTOT1

Frequency f2 (middle frequency):

CTOT2=CCOIL+CANT1+CANT2+CRFI1+COFF3=CCOIL+CANT1+CANT2+ 6.5pF+75pF3=CCOIL+CANT1+CANT2+ 81.5pF,

f 2 = 2π

1

L ANT ⋅ CTOT 2

Frequency f3 (lowest frequency):

CTOT3=CCOIL+CANT1+ CANT2+ CANT3+CRFI1=CCOIL+CANT1+ CANT2+ CANT3+6.5pF,

1

f 3 = 2π L ANT ⋅ CTOT 3

4 (9)

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