CC400-RTR2 datasheet(9/10 Pages) TI

9 / 10 page

CC400

SWRS050

Page 9 of 32

11.

Circuit Description

Figure 2: Simplified block diagram of the

CC400.

A simplified block diagram of

CC400 is

shown in Figure 2. Only signal pins are

shown.

In receive mode

CC400 is configured as a

traditional heterodyne receiver. The RF

input signal is amplified by the low-noise

amplifier (LNA) and converted down to the

intermediate frequency (IF) by the mixer

(MIXER). In the intermediate frequency

stage (IF STAGE) this downconverted

signal is amplified and filtered before being

fed to the demodulator (DEMOD). As an

option an external IF filter can be used for

improved performance. After demodulation

CC400 outputs the raw digital demodulated

data on the pin DIO. Synchronisation and

final qualification of the demodulated data

is done by the interfacing digital system

(microcontroller).

In transmit mode the voltage controlled

oscillator (VCO) output signal is fed

directly to the power amplifier (PA). The

RF output is frequency shift keyed (FSK)

by the digital bit stream fed to the pin DIO.

The internal T/R switch circuitry makes the

antenna interface and matching very easy.

The frequency synthesiser generates the

local oscillator signal which is fed to the

MIXER in receive mode and to PA in

transmit mode. The frequency synthesiser

consists of a crystal oscillator (XOSC),

phase

detector

(PD),

charge

pump

(CHARGE PUMP), VCO, and frequency

dividers (/R and /N). An external crystal

must be connected to XOSC, and an

external LC-tank with a varactor diode is

required for the VCO. For flexibility the

loop filter is external.

For chip configuration

CC400 includes a 3-

wire digital serial interface (CONTROL).

CLOCK, PDATA, STROBE

LNA

DEMOD

VCO

Freq. divider

OSC

MIXER

CHARGE

PUMP

VCO_IN

RF_IN

DIO

CHP_OUT

LOCK

IF STAGE

RF_OUT

IF_OUT IF_IN

CONTROL

XOSC_Q2

XOSC_Q1

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