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RF6001
Rev A3 DS050929
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Part of the POLARIS™ TOTAL RADIO™ Solution
GMSK to GMSK EALGN=0, “Alternate” FIFO Mode
The diagram below presents the transition between two GMSK timeslots in alternate mode.
The falling edge of TX_ST can be located in one of three positions to turn off the data after the last tail symbol of the first burst.
RD_DLY is adjusted depending on the qst chosen. The rising edge of TX_ST is aligned to be 14qst before the center of the first
tail symbol of the second burst so that the effective FIFO clock starts at the correct time to align the first tail symbol to the
desired time.
In GMSK mode there is a latency of approximately 12qst (12.2qst actually) from the center of a data symbol entering the mod-
ulator to the maximum RF effect of the symbol. Thus DAC1 is aligned with the “Data at output” field and is 12qst delayed from
the data at the output of the FIFO.
Note that none of the tail bits are punctured.
In this method of operation (EALGN=0) the rising edge of TX_ST for the second and later bursts must be an integer number of
symbol times relative to the first rising edge of TX_ST. The timing is aligned with the first rising edge of TX_ST and will not
change if subsequent TX_ST transitions are aligned to this raster. (Since G_DLY is not zero then if TXST moves off the raster the
system would realign the clocks as if EALGN=1.)
This means that the guard time will be an integer number of symbols and will ignore the quarter symbol shift specified by ETSI.
There will be no glitch in this mode.
12 qst
12 qst
RD_DLY=
11 qst to 13 qst
Center of
last tail bit
36qst
RU_DLY=
6 qst
Center of
first tail bit
14 qst
First GMSK
bit of next slot
Latency of GMSK
mod complete
NO tail symbols punctured
Effective FIFO
Output Clock
TXST
DAC1
Data at RF due to
GMSK Modulator
tail
tail
tail
data
G_DEF
tail
data
tail
tail
Data at
FIFO output
0
0
1
tail
tail
tail
data
tail
tail
11
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