RDA5876 datasheet(11/22 Pages) RDA

11 / 22 page

RDA Microelectronics, Inc.

RDA5876 Datasheet V1.2

Page 11 of 22

7 FM Section Functional Description

ADC

DAC

ADC

Audio

DSP

Core

digital filter

MPX decoder

stereo/mono

audio

VCO

Synthesizer

GPIO

Interface

Bus

RSSI

VIO

SDIO

SCLK

MCU

GPIO

LOUT

ROUT

LNAN

LNAP

RCLK

2.7-5.5 V

32.768 KHz

VDD

LDO

Limiter

LNA

PGA

RDS

/RBDS

Figure 7-1. RDA5876 FM Tuner Block Diagram

FM Receiver

The receiver uses a digital low-IF architecture that

avoids the difficulties associated with direct

conversion while delivering lower solution cost

and reduces complexity, and integrates a low

noise

amplifier

(LNA)

supporting

the

broadcast band (50 to 115MHz), a quadrature

image-reject mixer, a programmable gain control

(PGA),

high

resolution

analog-to-digital

converters (ADCs), an audio DSP and a high-

fidelity digital-to-analog converters (DACs).

The LNA has differential input ports (LNAP and

LNAN) and supports any input port by set

according registers bits (LNA_port_sel[1:0]). It

default input common mode voltage is GND.

The limiter prevents overloading and limits the

amount of intermodulation products created by

strong adjacent channels.

The quadrature mixer down converts the LNA

output differential RF signal to low-IF, it also has

image-reject function.

The PGA amplifies the mixer output IF signal and

then digitized with ADCs.

The DSP core finishes the channel selection, FM

demodulation, stereo MPX decoder and output

audio signal. The MPX decoder can autonomous

switch from stereo to mono to limit the output

noise.

The DACs convert digital audio signal to analog

and change the volume at same time. The DACs

has low-pass feature and -3dB frequency is about

30 KHz.

Synthesizer

The frequency synthesizer generates the local

oscillator signal which divide to quadrature, then

be used to downconvert the RF input to a

constant low intermediate frequency (IF). The

synthesizer reference clock is 32.768 KHz.

The synthesizer frequency is defined by bits

CHAN[9:0] with the range from 50MHz to

115MHz.

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