LMX5251_15 Datasheet, PDF (22/40 Pages) Texas Instruments – LMX5251 Bluetooth™ CMOS Radio

LMX5251
SNOSCW3A – FEBRUARY 2004 – REVISED APRIL 2013
TX_RX_DATA
83.3 ns
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BBP_CLOCK
LMX5251 asserts TX_RX_DATA;
Baseband Controller samples TX_RX_DATA.
Figure 13. Bluetooth Receive Data Timing
During transmit mode, the baseband controller controls the TX_RX_DATA line, and asserts the data from the
outgoing Bluetooth RF packet onto TX_RX_DATA at the rising edge of the BBP_CLOCK. The LMX5251 samples
the RX_DATA at the falling edge of BBP_CLOCK after a six BBP_CLOCK period delay, corresponding to a half
symbol time delay to allow for sampling at the middle of the data bit.
11µussec
TX _ RTXX__RDXA_TDAATA
Baseband Controller
in(tLeMrnPal ^{i1nMteHrnzaTl} X1cMlkHz
deTrXivBcelBdkPfdro_emCrivLeOdCfrKo)m
BBP_CLOCK
B B PB_BCPL_OCCLOKCK
Baseband CoLnMtroPller asserts TX_RX_DALTMA;X5250
LMaXs5s2e51rtssaTmXp_leRsXT_XD_ARTXA_DATAsamples TX_RX_DATA
Figure 14. Bluetooth Transmit Data Timing
Receive Mode Slot Timing
Prior to initiating the receive mode, the crystal oscillator must be turned on and settled such that the
BBP_CLOCK output is present. The baseband controller programs the LMX5251 receiver (RX) mode and
frequency information via the serial interface, at which point the LMX5251 PLL begins acquiring the correct RX
frequency channel. After ~100 µs, the receive chain powers up. RX data is then clocked to the baseband
controller. The serial port is used to program the LMX5251 out of receive mode.
The LMX5251 has built in flexibility for adjusting the TX_RX_SYNC timing. The default is for the TX_RX_SYNC
to go high at the middle of the third trailer bit, T2. The LMX5251 TX_RX_SYNC_del[1:0] programming bits adjust
for position of TX_RX_SYNC pulse with respect to center of the trailer bits ±0.5 µs (see Figure 15). When the
TX_RX_SYNC pulse goes high at T0, T1, T2, or T3, TX_RX_SYNC_del is set to 0, 1, 2, or 3 respectively. The
TX_RX_SYNC_del is set to the delay in usec of the TX_RX_SYNC rising edge relative to the leading edge of the
first trailer bit, T0. An example of the TX_RX_SYNC timing for the case when the trailer is 1010 is shown in
Figure 15.
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