CC113L Datasheet, PDF (44/75 Pages) Texas Instruments – Value Line Receiver

25.2 Calibration in Multi-Channel Systems
CC115L is highly suited for multi-channel
systems due to its agile frequency synthesizer
and effective communication interface.
Charge pump current, VCO current, and VCO
capacitance array calibration data is required
for each frequency when implementing a multi-
channel system. There are 3 ways of obtaining
the calibration data from the chip:
1) Calibration for every frequency change. The
PLL calibration time is 712/724 µs (26 MHz
crystal and TEST0 = 0x09/0B, see Table 27).
The blanking interval between each frequency
is then 787/799 µs.
2) Perform all necessary calibration at startup
and store the resulting FSCAL3, FSCAL2, and
FSCAL1 register values in MCU memory. The
VCO capacitance calibration FSCAL1 register
value must be found for each RF frequency to
be used. The VCO current calibration value
and the charge pump current calibration value
available in FSCAL2 and FSCAL3 respectively
are not dependent on the RF frequency, so the
same value can therefore be used for all RF
frequencies for these two registers. Between
each frequency change, the calibration
process can then be replaced by writing the
FSCAL3, FSCAL2 and FSCAL1 register values
that corresponds to the next RF frequency.
The PLL turn on time is approximately 75 µs
(Table 26). The blanking interval between
each frequency hop is then approximately
75 µs.
3) Run calibration on a single frequency at
startup. Next write 0 to FSCAL3[5:4] to
CC113L
disable the charge pump calibration. After
writing to FSCAL3[5:4], strobe SRX with
MCSM0.FS_AUTOCAL=1 for each new
frequency. That is, VCO current and VCO
capacitance calibration is done, but not charge
pump current calibration. When charge pump
current calibration is disabled the calibration
time is reduced from 712/724 µs to 145/157 µs
(26 MHz crystal and TEST0 = 0x09/0B, see
Table 27). The blanking interval between each
frequency hop is then 220/232 µs.
There is a trade-off between blanking time and
memory space needed for storing calibration
data in non-volatile memory. Solution 2) above
gives the shortest blanking interval, but
requires more memory space to store
calibration values. This solution also requires
that the supply voltage and temperature do not
vary much in order to have a robust solution.
Solution 3) gives 567 µs smaller blanking
interval than solution 1).
The
recommended
settings
for
TEST0.VCO_SEL_CAL_EN change with
frequency. This means that one should always
use SmartRF Studio [4] to get the correct
settings for a specific frequency before doing a
calibration, regardless of which calibration
method is being used.
Note: The content in the TEST0 register is
not retained in SLEEP state, thus it is
necessary to re-write this register when
returning from the SLEEP state.
SWRS108A
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