SX1211I084TRT(2007) Просмотр технического описания (PDF) - Semtech Corporation

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SX1211I084TRT
(Rev.:2007)

Lowest Power Integrated UHF Transceiver Short Range Devices

Semtech Corporation 

ADVANCED COMMUNICATIONS & SENSING

SX1211

3.3. Transmitter Description

The SX1211 is set to transmit mode when MCParam_Chip_mode = 100.

Amplification

Second

up-conversion

First up-conversion

Interpolation

filters

DACs

DDS

RFIO

PA

I

LO1 Tx

Q

I

LO2 Tx

Q

I

LO2 Tx

Q

Waveform

generator

Data

Clock

RF

IF

Baseband

Figure 7: Transmitter Architecture

3.3.1. Architecture Description

The baseband I and Q signals are digitally generated by a DDS whose digital to analog converters (DAC) followed

by two anti-aliasing low-pass filters transform the digital signal into analog in-phase (I) and quadrature (Q)

components whose frequency is the selected frequency deviation (Fdev).

1

Fdev

I(t)

Q(t)

Figure 8: I(t), Q(t) Overview

In FSK mode, the relative phase of I and Q is switched by the input data between -90° and +90° with co ntinuous

phase. The modulation is therefore performed at this initial stage, since the information contained in the phase

difference will be converted into a frequency shift when the I and Q signals are up-converted in the first mixer

stage. This first up-conversion stage is duplicated to enhance image rejection. The FSK convention is such that:

V3.0 – august 15th, 2007

Page 18 of 73

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