Rainbow-electronics AT86RF231 User Manual download pdf (Page 104)

104

8111A–AVR–05/08

AT86RF231

9.2 Transmitter (TX)

9.2.1 Overview

The AT86RF231 transmitter consists of a digital base band processor (TX BBP) and an analog

radio front end, see Figure 9-2 on page 104.

Figure 9-2. Transmitter Block Diagram

The TX BBP reads the frame data from the Frame Buffer and performs the bit-to-symbol and

symbol-to-chip mapping as specified by IEEE 802.15.4 in section 6.5.2. The O-QPSK modula-

tion signal is generated and fed into the analog radio front end.

The fractional-N frequency synthesizer (PLL) converts the baseband transmit signal to the RF

signal, which is amplified by the power amplifier (PA). The PA output is internally connected to

bidirectional differential antenna pins (RFP, RFN), so that no external antenna switch is needed.

9.2.2 Frame Transmit Procedure

The frame transmit procedure including writing PSDU data in the Frame Buffer and initiating a

transmission is described in Section 10.2 “Frame Transmit Procedure” on page 127, Frame

Transmit Procedure.

9.2.3 Configuration

The maximum output power of the transmitter is typically +3 dBm. The output power can be con-

figured via register bits TX_PWR (register 0x05, PHY_TX_PWR). The output power of the

transmitter can be controlled over a range of 20 dB.

A transmission can be started from PLL_ON or TX_ARET_ON state by a rising edge of pin

SLP_TR or by writing TX_START command to register bits TRX_CMD (register 0x02,

TRX_STATE).

9.2.4 TX Power Ramping

To optimize the output power spectral density (PSD), the PA buffer and PA are enabled sequen-

tially. This is illustrated by a timing example using default settings, shown in Figure 9-3 on page

105. In this example the transmission is initiated with the rising edge of pin 11 (SLP_TR). The

radio transceiver state changes from PLL_ON to BUSY_TX. The modulation starts 16 µs after

SLP_TR.

PLL – TX Modulation PA

Ext. RF front-end and

Output Power Control

SPI

I/F

DIG3/4

RFP

RFN

TX Data

Analog Domain Digital Domain

TX BBP

Frame

Buffer

Control, Registers

SPI

µC

I/F

Buf

1 2 ... 99 100 101 102 103 104 105 106 107 108 109 ... 179 180

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Rainbow-electronics AT86RF231 User Manual Page 104

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