RF6001_1 RFMD [RF Micro Devices], RF6001_1 Datasheet - Page 42

• Manufacturer Part Number: RF6001_1
• Description: FRACTIONAL-N RF SYNTHESIZER WITH MODULATOR AND DIGITAL IF FILTER
• Manufacturer: RFMD [RF Micro Devices]

RF6001
Part of the POLARIS™ TOTAL RADIO™ Solution
Control of guard bits using RF6001 in GMSK
In GMSK mode ETSI specifies that the guard bits are all ones and the tail bits are all zeroes. This results in a differentially
encoded output of 000000100ddddd. Where “d” represents the data bits.
If TX_DE is low then differential encoding is done in baseband. In this case DE_INIT is held at zero and G_DEF is held at zero.
The output to the GMSK modulator will be zero until MD_DLY1 expires. Once MD_DLY1 expires then TXDATA will port to the
GMSK modulator with differential encoding as defined by baseband. Thus MD_DLY1 timing is set to switch over at the first tail
bit.
If TX_DE is high then the differential encoding is done within the RF6001. In this case DE_INIT is held at one and G_DEF is held
at zero. The output of the internal differential encoder will then be zero for the guard bits and the internal state of the differen-
tial encoder will be held at one during this time. When MD_DLY1 expires then the input to the differential encoder will receive
a zero for the first tail bit. This will encode with the internal state of one to an output of one at the differential encoder. Subse-
quent tail bits of zero will differentially encode with the previous state and result in zero. MD_DLY1 will be timed to expire at the
first tail bit.
Note that when MD_DLY1 expires then this triggers GCNT to begin and all transitions actually occur when GCNT is done. If all
bits are valid then GCNT is zero and GCNT_done is the same as MD_DLY1 expiring.
Also note that GCNT works on the output data flow only in serial input mode. In FIFO mode GCNT works as the FIFO is loaded
but not when the FIFO is read. Thus GCNT is effectively zero in FIFO mode for data output.
Control of guard bits using Baseband in GMSK
This is a fairly trivial case. MD_DLY1 is set to expire some time before the ramp up interval. The baseband sends data and by
the time the transition from guard bits to tail bits occurs the differential encoder has been initialized long ago.
Detailed GPRS Burst Transition Operation
In a GPRS transmission multiple timeslots can be transmitted.
Several SDI parameters must be properly set to properly time the transitions. These parameters are as defined as follows: (All
of the previously defined parameters from the ramp up section still apply.)
MD_DLY2 (Modulation Delay 2)
In a GPRS transmission, when TX_ST falls at the end of the present TX timeslot, the data from the FIFO stops and the value of
G_DEF is used till MD_DLY2 expires. MD_DLY2 begins counting at the end of the present data bit being sent when TX_ST falls.
If UAM is true then MD_DLY2 begins counting at the next rising edge of TX_ST. Data will continue to be taken from GDEF until
MD_DLY2 expires and then will switch to the FIFO or the serial interface.
UAM (use Alternate Mode)
The RF6001 has two modes of transitioning between GPRS timeslots. This first mode uses MD_DLY2 to trigger the data flow
and TX_ST edges to start the ramps. This is referred to as the “normal” mode. If UAM is set high then the “alternate” mode of
operation is activated. In this mode TX_ST triggers the data flow. Ramp up and ramp down are then controlled by two timers
triggered from TX_ST as described below.
RD_DLY (Ramp Down Delay)
RD_DLY is a 5-bit field that will determine the start of the ramp down relative to the falling edge of TX_ST in quarter symbol
times (qst). This is only used if UAM is true.
RU_DLY (Ramp Up Delay)
RU_DLY is a 5-bit field that will determine the start of the ramp up relative to the rising edge of TX_ST in qsts. This is only used
if UAM is true.
In order to properly align the data upon making a transition between modes, the rising edge of TX_ST must be aligned to the
data stream.
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Rev A3 DS050929