XE1218A データシートの表示（PDF） - Unspecified

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XE1218A

Low power single die FM receiver

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Datasheet XE1218A: Low

Power single die FM receiver

1.3.2 Audio output stage

An integrated power amplifier (PA) allows for a direct connection to an earphone. Controlled by an external

potentiometer (100kΩ) a maximum attenuation of 10dB is achievable on the EAR output, 21.5dB with 1MΩ. A

high impedance line out (10kΩ) is available through the pad OUT.

2. Functional implementation

2.1 Block diagram

A1

VCC

VCC

C1

L1

RFT

VCCR VCCA VDD

AUD

C4

RFI

LNA

C5

L4

RFG

OSC

FM

DEMOD

AFC

LOP

LON

XP

XN

VM

VSS

L3

C3

L2

C2

Xtal

VCC

VCCO

Audio

SW

OUT

Line OUT

PA

EAR

XE1218 VOL

R1

Volume

Control

2.2 Operation overview

While the XE1218A is a single channel receiver, various fixed frequencies can be selected between 130MHz

and 230MHz. This is achieved by changing the external RF front-end components: L1, L2, L3, L4, C1, C2, C4,

C5 and Xtal. The XE1218A FM receiver connects to the antenna via a differential input: pins RFI and RFG. The

external components L4, C4 and C5 must tune the circuit to the incoming carrier frequency. L2 and C2 are

calculated to tune the oscillator to the desired incoming carrier frequency. Xtal is selected according to the

desired input carrier frequency, L3 relaxes the oscillator’s Q factor to insure greater reception stability.

Reception sensitivity is determined through the LNA’s external tank circuit: C1 and L1.

Two types of audio outputs can be selected: OUT (line out, 10kΩ output impedance) to connect to an external

audio processing circuit or amplifier and EAR for direct connection to an earphone. An external R1 is used to

adjust the volume through pin VOL. The internal RF and audio blocks each have their own supply voltage as

well as a common VDD. Clean voltage must be supplied to each of these supplies (VCCR, VCCA, VCCO and

VDD).

4

D0204-157

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