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42073A-MCU Wireless-02/13
ATmega2564/1284/644RFR2
9.6.2 Transmitter (TX)
9.6.2.1 Overview
The transmitter consists of a digital base band processor (TX BBP) and an analog front
end as shown in the following figure.
Figure 9-22. Transmitter Block Diagram
PLL – TX M odulation
PA
Ext. R F front-end and
Output Power C ontrol
D IG3/4
R FP
R FN
TX D ata
Analog D om ain
TX BBP
Control
Buf
D igital Dom ain
Fram e
Buffer
C
I/F
R egisters
I/O
M em ory
Space
$01FF
$017F
$0180
$0140
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 modulation 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.
9.6.2.2 Frame Transmit Procedure
The frame transmit procedure including writing PSDU data in the Frame Buffer and
91. The controller must ensure to provide valid frame data before starting the frame
transmission. For save operation, it is recommended to write the complete frame into
the Frame Buffer before starting the frame transmission.
9.6.2.3 Configuration
The maximum output power of the transmitter is typically +3.5 dBm. The output power
can be configured via the TX_PWR bits of register PHY_TX_PWR. The output power of
the transmitter can be controlled over a 20 dB range.
A transmission can be started from PLL_ON or TX_ARET_ON state by writing ‘1’ to bit
SLPTR of the TRXPR register or by writing TX_START command to the TRX_CMD bits
of register TRX_STATE.
9.6.2.4 TX Power Ramping
To optimize the TX output power spectral density (PSD) the TX may be controlled by
register PHY_TX_PWR and PARCR. The PA ramps up prior to TX data sent and ramps
down after the TX data are completed. The signal sent during PA ramp up/down
process is not modulated. The PLL frequency (+500kHz or -500kHz relative to carrier
frequency) may be selected, separate for the PA ramp up and down process.
A timing example using default settings illustrates the sequence in the next figure. In
this example the transmission is initiated with the rising edge of the SLPTR bit. The
modulation starts 16 s after SLPTR.